Add is_dll_import to @extern, to support __declspec(dllimport) with the MSVC ABI

lib/std/builtin.zig

@@ -683,6 +683,7 @@ pub const ExternOptions = struct {
  library_name: ?[]const u8 = null,
  linkage: GlobalLinkage = .strong,
  is_thread_local: bool = false,
+ is_dll_import: bool = false,
 };
 
 /// This data structure is used by the Zig language code generation and

src/InternPool.zig

@@ -2054,6 +2054,7 @@ pub const Key = union(enum) {
  is_const: bool,
  is_threadlocal: bool,
  is_weak_linkage: bool,
+ is_dll_import: bool,
  alignment: Alignment,
  @"addrspace": std.builtin.AddressSpace,
  /// The ZIR instruction which created this extern; used only for source locations.
@@ -2675,7 +2676,8 @@ pub const Key = union(enum) {
  asBytes(&e.ty) ++ asBytes(&e.lib_name) ++
  asBytes(&e.is_const) ++ asBytes(&e.is_threadlocal) ++
  asBytes(&e.is_weak_linkage) ++ asBytes(&e.alignment) ++
- asBytes(&e.@"addrspace") ++ asBytes(&e.zir_index)),
+ asBytes(&e.is_dll_import) ++ asBytes(&e.@"addrspace") ++
+ asBytes(&e.zir_index)),
  };
  }
 
@@ -2771,6 +2773,7 @@ pub const Key = union(enum) {
  a_info.is_const == b_info.is_const and
  a_info.is_threadlocal == b_info.is_threadlocal and
  a_info.is_weak_linkage == b_info.is_weak_linkage and
+ a_info.is_dll_import == b_info.is_dll_import and
  a_info.alignment == b_info.alignment and
  a_info.@"addrspace" == b_info.@"addrspace" and
  a_info.zir_index == b_info.zir_index;
@@ -5370,7 +5373,8 @@ pub const Tag = enum(u8) {
  is_const: bool,
  is_threadlocal: bool,
  is_weak_linkage: bool,
- _: u29 = 0,
+ is_dll_import: bool,
+ _: u28 = 0,
  };
  };
 
@@ -6715,6 +6719,7 @@ pub fn indexToKey(ip: *const InternPool, index: Index) Key {
  .is_const = extra.flags.is_const,
  .is_threadlocal = extra.flags.is_threadlocal,
  .is_weak_linkage = extra.flags.is_weak_linkage,
+ .is_dll_import = extra.flags.is_dll_import,
  .alignment = nav.status.resolved.alignment,
  .@"addrspace" = nav.status.resolved.@"addrspace",
  .zir_index = extra.zir_index,
@@ -7381,6 +7386,7 @@ pub fn get(ip: *InternPool, gpa: Allocator, tid: Zcu.PerThread.Id, key: Key) All
  .is_const = false,
  .is_threadlocal = variable.is_threadlocal,
  .is_weak_linkage = variable.is_weak_linkage,
+ .is_dll_import = false,
  },
  }),
  });
@@ -8644,6 +8650,7 @@ pub fn getExtern(
  .is_const = key.is_const,
  .is_threadlocal = key.is_threadlocal,
  .is_weak_linkage = key.is_weak_linkage,
+ .is_dll_import = key.is_dll_import,
  },
  .zir_index = key.zir_index,
  .owner_nav = owner_nav,

src/Sema.zig

@@ -876,6 +876,7 @@ const InferredAlloc = struct {
 
 const NeededComptimeReason = struct {
  needed_comptime_reason: []const u8,
+ value_comptime_reason: ?[]const u8 = null,
  block_comptime_reason: ?*const Block.ComptimeReason = null,
 };
 
@@ -2251,7 +2252,7 @@ fn resolveValueAllowVariables(sema: *Sema, inst: Air.Inst.Ref) CompileError!?Val
  }
  };
  const val = Value.fromInterned(ip_index);
- if (val.isPtrToThreadLocal(pt.zcu)) return null;
+ if (val.isPtrRuntimeValue(pt.zcu)) return null;
  return val;
 }
 
@@ -2277,8 +2278,14 @@ pub fn resolveFinalDeclValue(
  const zcu = sema.pt.zcu;
 
  const val = try sema.resolveValueAllowVariables(air_ref) orelse {
+ const value_comptime_reason: ?[]const u8 = if (air_ref.toInterned()) |_|
+ "thread local and dll imported variables have runtime-known addresses"
+ else
+ null;
+
  return sema.failWithNeededComptime(block, src, .{
  .needed_comptime_reason = "global variable initializer must be comptime-known",
+ .value_comptime_reason = value_comptime_reason,
  });
  };
  if (val.isGenericPoison()) return error.GenericPoison;
@@ -2296,6 +2303,9 @@ fn failWithNeededComptime(sema: *Sema, block: *Block, src: LazySrcLoc, reason: N
  const msg = try sema.errMsg(src, "unable to resolve comptime value", .{});
  errdefer msg.destroy(sema.gpa);
  try sema.errNote(src, msg, "{s}", .{reason.needed_comptime_reason});
+ if (reason.value_comptime_reason) |value_comptime_reason| {
+ try sema.errNote(src, msg, "{s}", .{value_comptime_reason});
+ }
 
  if (reason.block_comptime_reason) |block_comptime_reason| {
  try block_comptime_reason.explain(sema, msg);
@@ -9960,6 +9970,7 @@ fn funcCommon(
  .is_const = true,
  .is_threadlocal = false,
  .is_weak_linkage = false,
+ .is_dll_import = false,
  .alignment = alignment orelse .none,
  .@"addrspace" = address_space orelse .generic,
  .zir_index = sema.getOwnerCauDeclInst(), // `declaration` instruction
@@ -26505,6 +26516,7 @@ fn zirVarExtended(
  .is_const = small.is_const,
  .is_threadlocal = small.is_threadlocal,
  .is_weak_linkage = false,
+ .is_dll_import = false,
  .alignment = alignment,
  .@"addrspace" = @"addrspace",
  .zir_index = sema.getOwnerCauDeclInst(), // `declaration` instruction
@@ -26958,6 +26970,7 @@ fn resolveExternOptions(
  library_name: InternPool.OptionalNullTerminatedString = .none,
  linkage: std.builtin.GlobalLinkage = .strong,
  is_thread_local: bool = false,
+ is_dll_import: bool = false,
 } {
  const pt = sema.pt;
  const zcu = pt.zcu;
@@ -26971,6 +26984,7 @@ fn resolveExternOptions(
  const library_src = block.src(.{ .init_field_library = src.offset.node_offset_builtin_call_arg.builtin_call_node });
  const linkage_src = block.src(.{ .init_field_linkage = src.offset.node_offset_builtin_call_arg.builtin_call_node });
  const thread_local_src = block.src(.{ .init_field_thread_local = src.offset.node_offset_builtin_call_arg.builtin_call_node });
+ const dll_import_src = block.src(.{ .init_field_dll_import = src.offset.node_offset_builtin_call_arg.builtin_call_node });
 
  const name_ref = try sema.fieldVal(block, src, options, try ip.getOrPutString(gpa, pt.tid, "name", .no_embedded_nulls), name_src);
  const name = try sema.toConstString(block, name_src, name_ref, .{
@@ -27004,6 +27018,11 @@ fn resolveExternOptions(
  break :library_name library_name;
  } else null;
 
+ const is_dll_import_ref = try sema.fieldVal(block, src, options, try ip.getOrPutString(gpa, pt.tid, "is_dll_import", .no_embedded_nulls), dll_import_src);
+ const is_dll_import_val = try sema.resolveConstDefinedValue(block, dll_import_src, is_dll_import_ref, .{
+ .needed_comptime_reason = "it must be comptime-known if the symbol is imported from a dll",
+ });
+
  if (name.len == 0) {
  return sema.fail(block, name_src, "extern symbol name cannot be empty", .{});
  }
@@ -27017,6 +27036,7 @@ fn resolveExternOptions(
  .library_name = try ip.getOrPutStringOpt(gpa, pt.tid, library_name, .no_embedded_nulls),
  .linkage = linkage,
  .is_thread_local = is_thread_local_val.toBool(),
+ .is_dll_import = is_dll_import_val.toBool(),
  };
 }
 
@@ -27062,6 +27082,7 @@ fn zirBuiltinExtern(
  .is_const = ptr_info.flags.is_const,
  .is_threadlocal = options.is_thread_local,
  .is_weak_linkage = options.linkage == .weak,
+ .is_dll_import = options.is_dll_import,
  .alignment = ptr_info.flags.alignment,
  .@"addrspace" = ptr_info.flags.address_space,
  // This instruction is just for source locations.

src/Value.zig

@@ -1340,11 +1340,11 @@ pub fn isLazySize(val: Value, zcu: *Zcu) bool {
  };
 }
 
-pub fn isPtrToThreadLocal(val: Value, zcu: *Zcu) bool {
+pub fn isPtrRuntimeValue(val: Value, zcu: *Zcu) bool {
  const ip = &zcu.intern_pool;
  const nav = ip.getBackingNav(val.toIntern()).unwrap() orelse return false;
  return switch (ip.indexToKey(ip.getNav(nav).status.resolved.val)) {
- .@"extern" => |e| e.is_threadlocal,
+ .@"extern" => |e| e.is_threadlocal or e.is_dll_import,
  .variable => |v| v.is_threadlocal,
  else => false,
  };

src/Zcu.zig

@@ -1522,6 +1522,7 @@ pub const SrcLoc = struct {
  .init_field_cache,
  .init_field_library,
  .init_field_thread_local,
+ .init_field_dll_import,
  => |builtin_call_node| {
  const wanted = switch (src_loc.lazy) {
  .init_field_name => "name",
@@ -1533,6 +1534,7 @@ pub const SrcLoc = struct {
  .init_field_cache => "cache",
  .init_field_library => "library",
  .init_field_thread_local => "thread_local",
+ .init_field_dll_import => "dll_import",
  else => unreachable,
  };
  const tree = try src_loc.file_scope.getTree(gpa);
@@ -1959,6 +1961,7 @@ pub const LazySrcLoc = struct {
  init_field_cache: i32,
  init_field_library: i32,
  init_field_thread_local: i32,
+ init_field_dll_import: i32,
  /// The source location points to the value of an item in a specific
  /// case of a `switch`.
  switch_case_item: SwitchItem,

src/Zcu/PerThread.zig

@@ -2763,6 +2763,7 @@ pub fn getCoerced(pt: Zcu.PerThread, val: Value, new_ty: Type) Allocator.Error!V
  .is_const = e.is_const,
  .is_threadlocal = e.is_threadlocal,
  .is_weak_linkage = e.is_weak_linkage,
+ .is_dll_import = e.is_dll_import,
  .alignment = e.alignment,
  .@"addrspace" = e.@"addrspace",
  .zir_index = e.zir_index,

src/codegen/llvm.zig

@@ -3237,10 +3237,10 @@ pub const Object = struct {
  const ip = &zcu.intern_pool;
  const nav = ip.getNav(nav_index);
  const resolved = nav.status.resolved;
- const is_extern, const is_threadlocal, const is_weak_linkage = switch (ip.indexToKey(resolved.val)) {
- .variable => |variable| .{ false, variable.is_threadlocal, variable.is_weak_linkage },
- .@"extern" => |@"extern"| .{ true, @"extern".is_threadlocal, @"extern".is_weak_linkage },
- else => .{ false, false, false },
+ const is_extern, const is_threadlocal, const is_weak_linkage, const is_dll_import = switch (ip.indexToKey(resolved.val)) {
+ .variable => |variable| .{ false, variable.is_threadlocal, variable.is_weak_linkage, false },
+ .@"extern" => |@"extern"| .{ true, @"extern".is_threadlocal, @"extern".is_weak_linkage, @"extern".is_dll_import },
+ else => .{ false, false, false, false },
  };
 
  const variable_index = try o.builder.addVariable(
@@ -3257,6 +3257,7 @@ pub const Object = struct {
  if (is_threadlocal and !zcu.navFileScope(nav_index).mod.single_threaded)
  variable_index.setThreadLocal(.generaldynamic, &o.builder);
  if (is_weak_linkage) variable_index.setLinkage(.extern_weak, &o.builder);
+ if (is_dll_import) variable_index.setDllStorageClass(.dllimport, &o.builder);
  } else {
  variable_index.setLinkage(.internal, &o.builder);
  variable_index.setUnnamedAddr(.unnamed_addr, &o.builder);
@@ -4782,10 +4783,10 @@ pub const NavGen = struct {
  const nav = ip.getNav(nav_index);
  const resolved = nav.status.resolved;
 
- const is_extern, const lib_name, const is_threadlocal, const is_weak_linkage, const is_const, const init_val, const owner_nav = switch (ip.indexToKey(resolved.val)) {
- .variable => |variable| .{ false, variable.lib_name, variable.is_threadlocal, variable.is_weak_linkage, false, variable.init, variable.owner_nav },
- .@"extern" => |@"extern"| .{ true, @"extern".lib_name, @"extern".is_threadlocal, @"extern".is_weak_linkage, @"extern".is_const, .none, @"extern".owner_nav },
- else => .{ false, .none, false, false, true, resolved.val, nav_index },
+ const is_extern, const lib_name, const is_threadlocal, const is_weak_linkage, const is_dll_import, const is_const, const init_val, const owner_nav = switch (ip.indexToKey(resolved.val)) {
+ .variable => |variable| .{ false, variable.lib_name, variable.is_threadlocal, variable.is_weak_linkage, false, false, variable.init, variable.owner_nav },
+ .@"extern" => |@"extern"| .{ true, @"extern".lib_name, @"extern".is_threadlocal, @"extern".is_weak_linkage, @"extern".is_dll_import, @"extern".is_const, .none, @"extern".owner_nav },
+ else => .{ false, .none, false, false, false, true, resolved.val, nav_index },
  };
  const ty = Type.fromInterned(nav.typeOf(ip));
 
@@ -4860,8 +4861,11 @@ pub const NavGen = struct {
  try global_index.rename(decl_name, &o.builder);
  global_index.setLinkage(.external, &o.builder);
  global_index.setUnnamedAddr(.default, &o.builder);
- if (zcu.comp.config.dll_export_fns)
+ if (is_dll_import) {
+ global_index.setDllStorageClass(.dllimport, &o.builder);
+ } else if (zcu.comp.config.dll_export_fns) {
  global_index.setDllStorageClass(.default, &o.builder);
+ }
 
  if (is_weak_linkage) global_index.setLinkage(.extern_weak, &o.builder);
  }

src/codegen/llvm/Builder.zig

@@ -2528,6 +2528,10 @@ pub const Variable = struct {
  return self.ptrConst(builder).global.setLinkage(linkage, builder);
  }
 
+ pub fn setDllStorageClass(self: Index, class: DllStorageClass, builder: *Builder) void {
+ return self.ptrConst(builder).global.setDllStorageClass(class, builder);
+ }
+
  pub fn setUnnamedAddr(self: Index, unnamed_addr: UnnamedAddr, builder: *Builder) void {
  return self.ptrConst(builder).global.setUnnamedAddr(unnamed_addr, builder);
  }

test/cases/compile_errors/builtin_extern_in_comptime_scope.zig

@@ -0,0 +1,18 @@
+const foo_tl = @extern(*i32, .{ .name = "foo", .is_thread_local = true });
+const foo_dll = @extern(*i32, .{ .name = "foo", .is_dll_import = true });
+pub export fn entry() void {
+ _ = foo_tl;
+}
+pub export fn entry2() void {
+ _ = foo_dll;
+}
+// error
+// backend=stage2
+// target=native
+//
+// :1:16: error: unable to resolve comptime value
+// :1:16: note: global variable initializer must be comptime-known
+// :1:16: note: thread local and dll imported variables have runtime-known addresses
+// :2:17: error: unable to resolve comptime value
+// :2:17: note: global variable initializer must be comptime-known
+// :2:17: note: thread local and dll imported variables have runtime-known addresses

test/standalone/extern/build.zig

@@ -1,6 +1,9 @@
 const std = @import("std");
 
 pub fn build(b: *std.Build) void {
+ const test_step = b.step("test", "Test it");
+ b.default_step = test_step;
+
  const optimize: std.builtin.OptimizeMode = .Debug;
 
  const obj = b.addObject(.{
@@ -9,12 +12,20 @@ pub fn build(b: *std.Build) void {
  .target = b.graph.host,
  .optimize = optimize,
  });
- const main = b.addTest(.{
+ const shared = b.addSharedLibrary(.{
+ .name = "shared",
+ .target = b.graph.host,
+ .optimize = optimize,
+ .link_libc = true,
+ });
+ if (b.graph.host.result.abi == .msvc) shared.defineCMacro("API", "__declspec(dllexport)");
+ shared.addCSourceFile(.{ .file = b.path("shared.c"), .flags = &.{} });
+ const test_exe = b.addTest(.{
  .root_source_file = b.path("main.zig"),
  .optimize = optimize,
  });
- main.addObject(obj);
+ test_exe.addObject(obj);
+ test_exe.linkLibrary(shared);
 
- const test_step = b.step("test", "Test it");
- test_step.dependOn(&main.step);
+ test_step.dependOn(&b.addRunArtifact(test_exe).step);
 }

test/standalone/extern/main.zig

@@ -1,4 +1,5 @@
 const assert = @import("std").debug.assert;
+const testing = @import("std").testing;
 
 const updateHidden = @extern(*const fn (u32) callconv(.C) void, .{ .name = "updateHidden" });
 const getHidden = @extern(*const fn () callconv(.C) u32, .{ .name = "getHidden" });
@@ -8,14 +9,18 @@ const T = extern struct { x: u32 };
 test {
  const mut_val_ptr = @extern(*f64, .{ .name = "mut_val" });
  const const_val_ptr = @extern(*const T, .{ .name = "const_val" });
+ const shared_val_ptr = @extern(*c_int, .{ .name = "shared_val", .is_dll_import = true });
 
  assert(getHidden() == 0);
  updateHidden(123);
  assert(getHidden() == 123);
-
  assert(mut_val_ptr.* == 1.23);
  mut_val_ptr.* = 10.0;
  assert(mut_val_ptr.* == 10.0);
 
  assert(const_val_ptr.x == 42);
+
+ assert(shared_val_ptr.* == 1234);
+ shared_val_ptr.* = 1235;
+ assert(shared_val_ptr.* == 1235);
 }

test/standalone/extern/shared.c

@@ -0,0 +1,5 @@
+#ifndef API
+#define API
+#endif
+
+API int shared_val = 1234;

lib/std/builtin.zig

@@ -683,6 +683,7 @@ pub const ExternOptions = struct {
  library_name: ?[]const u8 = null,
  linkage: GlobalLinkage = .strong,
  is_thread_local: bool = false,
+ is_dll_import: bool = false,
 };
 
 /// This data structure is used by the Zig language code generation and

src/InternPool.zig

@@ -2054,6 +2054,7 @@ pub const Key = union(enum) {
  is_const: bool,
  is_threadlocal: bool,
  is_weak_linkage: bool,
+ is_dll_import: bool,
  alignment: Alignment,
  @"addrspace": std.builtin.AddressSpace,
  /// The ZIR instruction which created this extern; used only for source locations.
@@ -2675,7 +2676,8 @@ pub const Key = union(enum) {
  asBytes(&e.ty) ++ asBytes(&e.lib_name) ++
  asBytes(&e.is_const) ++ asBytes(&e.is_threadlocal) ++
  asBytes(&e.is_weak_linkage) ++ asBytes(&e.alignment) ++
- asBytes(&e.@"addrspace") ++ asBytes(&e.zir_index)),
+ asBytes(&e.is_dll_import) ++ asBytes(&e.@"addrspace") ++
+ asBytes(&e.zir_index)),
  };
  }
 
@@ -2771,6 +2773,7 @@ pub const Key = union(enum) {
  a_info.is_const == b_info.is_const and
  a_info.is_threadlocal == b_info.is_threadlocal and
  a_info.is_weak_linkage == b_info.is_weak_linkage and
+ a_info.is_dll_import == b_info.is_dll_import and
  a_info.alignment == b_info.alignment and
  a_info.@"addrspace" == b_info.@"addrspace" and
  a_info.zir_index == b_info.zir_index;
@@ -5370,7 +5373,8 @@ pub const Tag = enum(u8) {
  is_const: bool,
  is_threadlocal: bool,
  is_weak_linkage: bool,
- _: u29 = 0,
+ is_dll_import: bool,
+ _: u28 = 0,
  };
  };
 
@@ -6715,6 +6719,7 @@ pub fn indexToKey(ip: *const InternPool, index: Index) Key {
  .is_const = extra.flags.is_const,
  .is_threadlocal = extra.flags.is_threadlocal,
  .is_weak_linkage = extra.flags.is_weak_linkage,
+ .is_dll_import = extra.flags.is_dll_import,
  .alignment = nav.status.resolved.alignment,
  .@"addrspace" = nav.status.resolved.@"addrspace",
  .zir_index = extra.zir_index,
@@ -7381,6 +7386,7 @@ pub fn get(ip: *InternPool, gpa: Allocator, tid: Zcu.PerThread.Id, key: Key) All
  .is_const = false,
  .is_threadlocal = variable.is_threadlocal,
  .is_weak_linkage = variable.is_weak_linkage,
+ .is_dll_import = false,
  },
  }),
  });
@@ -8644,6 +8650,7 @@ pub fn getExtern(
  .is_const = key.is_const,
  .is_threadlocal = key.is_threadlocal,
  .is_weak_linkage = key.is_weak_linkage,
+ .is_dll_import = key.is_dll_import,
  },
  .zir_index = key.zir_index,
  .owner_nav = owner_nav,

src/Sema.zig

@@ -876,6 +876,7 @@ const InferredAlloc = struct {
 
 const NeededComptimeReason = struct {
  needed_comptime_reason: []const u8,
+ value_comptime_reason: ?[]const u8 = null,
  block_comptime_reason: ?*const Block.ComptimeReason = null,
 };
 
@@ -2251,7 +2252,7 @@ fn resolveValueAllowVariables(sema: *Sema, inst: Air.Inst.Ref) CompileError!?Val
  }
  };
  const val = Value.fromInterned(ip_index);
- if (val.isPtrToThreadLocal(pt.zcu)) return null;
+ if (val.isPtrRuntimeValue(pt.zcu)) return null;
  return val;
 }
 
@@ -2277,8 +2278,14 @@ pub fn resolveFinalDeclValue(
  const zcu = sema.pt.zcu;
 
  const val = try sema.resolveValueAllowVariables(air_ref) orelse {
+ const value_comptime_reason: ?[]const u8 = if (air_ref.toInterned()) |_|
+ "thread local and dll imported variables have runtime-known addresses"
+ else
+ null;
+
  return sema.failWithNeededComptime(block, src, .{
  .needed_comptime_reason = "global variable initializer must be comptime-known",
+ .value_comptime_reason = value_comptime_reason,
  });
  };
  if (val.isGenericPoison()) return error.GenericPoison;
@@ -2296,6 +2303,9 @@ fn failWithNeededComptime(sema: *Sema, block: *Block, src: LazySrcLoc, reason: N
  const msg = try sema.errMsg(src, "unable to resolve comptime value", .{});
  errdefer msg.destroy(sema.gpa);
  try sema.errNote(src, msg, "{s}", .{reason.needed_comptime_reason});
+ if (reason.value_comptime_reason) |value_comptime_reason| {
+ try sema.errNote(src, msg, "{s}", .{value_comptime_reason});
+ }
 
  if (reason.block_comptime_reason) |block_comptime_reason| {
  try block_comptime_reason.explain(sema, msg);
@@ -9960,6 +9970,7 @@ fn funcCommon(
  .is_const = true,
  .is_threadlocal = false,
  .is_weak_linkage = false,
+ .is_dll_import = false,
  .alignment = alignment orelse .none,
  .@"addrspace" = address_space orelse .generic,
  .zir_index = sema.getOwnerCauDeclInst(), // `declaration` instruction
@@ -26505,6 +26516,7 @@ fn zirVarExtended(
  .is_const = small.is_const,
  .is_threadlocal = small.is_threadlocal,
  .is_weak_linkage = false,
+ .is_dll_import = false,
  .alignment = alignment,
  .@"addrspace" = @"addrspace",
  .zir_index = sema.getOwnerCauDeclInst(), // `declaration` instruction
@@ -26958,6 +26970,7 @@ fn resolveExternOptions(
  library_name: InternPool.OptionalNullTerminatedString = .none,
  linkage: std.builtin.GlobalLinkage = .strong,
  is_thread_local: bool = false,
+ is_dll_import: bool = false,
 } {
  const pt = sema.pt;
  const zcu = pt.zcu;
@@ -26971,6 +26984,7 @@ fn resolveExternOptions(
  const library_src = block.src(.{ .init_field_library = src.offset.node_offset_builtin_call_arg.builtin_call_node });
  const linkage_src = block.src(.{ .init_field_linkage = src.offset.node_offset_builtin_call_arg.builtin_call_node });
  const thread_local_src = block.src(.{ .init_field_thread_local = src.offset.node_offset_builtin_call_arg.builtin_call_node });
+ const dll_import_src = block.src(.{ .init_field_dll_import = src.offset.node_offset_builtin_call_arg.builtin_call_node });
 
  const name_ref = try sema.fieldVal(block, src, options, try ip.getOrPutString(gpa, pt.tid, "name", .no_embedded_nulls), name_src);
  const name = try sema.toConstString(block, name_src, name_ref, .{
@@ -27004,6 +27018,11 @@ fn resolveExternOptions(
  break :library_name library_name;
  } else null;
 
+ const is_dll_import_ref = try sema.fieldVal(block, src, options, try ip.getOrPutString(gpa, pt.tid, "is_dll_import", .no_embedded_nulls), dll_import_src);
+ const is_dll_import_val = try sema.resolveConstDefinedValue(block, dll_import_src, is_dll_import_ref, .{
+ .needed_comptime_reason = "it must be comptime-known if the symbol is imported from a dll",
+ });
+
  if (name.len == 0) {
  return sema.fail(block, name_src, "extern symbol name cannot be empty", .{});
  }
@@ -27017,6 +27036,7 @@ fn resolveExternOptions(
  .library_name = try ip.getOrPutStringOpt(gpa, pt.tid, library_name, .no_embedded_nulls),
  .linkage = linkage,
  .is_thread_local = is_thread_local_val.toBool(),
+ .is_dll_import = is_dll_import_val.toBool(),
  };
 }
 
@@ -27062,6 +27082,7 @@ fn zirBuiltinExtern(
  .is_const = ptr_info.flags.is_const,
  .is_threadlocal = options.is_thread_local,
  .is_weak_linkage = options.linkage == .weak,
+ .is_dll_import = options.is_dll_import,
  .alignment = ptr_info.flags.alignment,
  .@"addrspace" = ptr_info.flags.address_space,
  // This instruction is just for source locations.

src/Value.zig

@@ -1340,11 +1340,11 @@ pub fn isLazySize(val: Value, zcu: *Zcu) bool {
  };
 }
 
-pub fn isPtrToThreadLocal(val: Value, zcu: *Zcu) bool {
+pub fn isPtrRuntimeValue(val: Value, zcu: *Zcu) bool {
  const ip = &zcu.intern_pool;
  const nav = ip.getBackingNav(val.toIntern()).unwrap() orelse return false;
  return switch (ip.indexToKey(ip.getNav(nav).status.resolved.val)) {
- .@"extern" => |e| e.is_threadlocal,
+ .@"extern" => |e| e.is_threadlocal or e.is_dll_import,
  .variable => |v| v.is_threadlocal,
  else => false,
  };

src/Zcu.zig

@@ -1522,6 +1522,7 @@ pub const SrcLoc = struct {
  .init_field_cache,
  .init_field_library,
  .init_field_thread_local,
+ .init_field_dll_import,
  => |builtin_call_node| {
  const wanted = switch (src_loc.lazy) {
  .init_field_name => "name",
@@ -1533,6 +1534,7 @@ pub const SrcLoc = struct {
  .init_field_cache => "cache",
  .init_field_library => "library",
  .init_field_thread_local => "thread_local",
+ .init_field_dll_import => "dll_import",
  else => unreachable,
  };
  const tree = try src_loc.file_scope.getTree(gpa);
@@ -1959,6 +1961,7 @@ pub const LazySrcLoc = struct {
  init_field_cache: i32,
  init_field_library: i32,
  init_field_thread_local: i32,
+ init_field_dll_import: i32,
  /// The source location points to the value of an item in a specific
  /// case of a `switch`.
  switch_case_item: SwitchItem,

src/Zcu/PerThread.zig

@@ -2763,6 +2763,7 @@ pub fn getCoerced(pt: Zcu.PerThread, val: Value, new_ty: Type) Allocator.Error!V
  .is_const = e.is_const,
  .is_threadlocal = e.is_threadlocal,
  .is_weak_linkage = e.is_weak_linkage,
+ .is_dll_import = e.is_dll_import,
  .alignment = e.alignment,
  .@"addrspace" = e.@"addrspace",
  .zir_index = e.zir_index,

src/codegen/llvm.zig

@@ -3237,10 +3237,10 @@ pub const Object = struct {
  const ip = &zcu.intern_pool;
  const nav = ip.getNav(nav_index);
  const resolved = nav.status.resolved;
- const is_extern, const is_threadlocal, const is_weak_linkage = switch (ip.indexToKey(resolved.val)) {
- .variable => |variable| .{ false, variable.is_threadlocal, variable.is_weak_linkage },
- .@"extern" => |@"extern"| .{ true, @"extern".is_threadlocal, @"extern".is_weak_linkage },
- else => .{ false, false, false },
+ const is_extern, const is_threadlocal, const is_weak_linkage, const is_dll_import = switch (ip.indexToKey(resolved.val)) {
+ .variable => |variable| .{ false, variable.is_threadlocal, variable.is_weak_linkage, false },
+ .@"extern" => |@"extern"| .{ true, @"extern".is_threadlocal, @"extern".is_weak_linkage, @"extern".is_dll_import },
+ else => .{ false, false, false, false },
  };
 
  const variable_index = try o.builder.addVariable(
@@ -3257,6 +3257,7 @@ pub const Object = struct {
  if (is_threadlocal and !zcu.navFileScope(nav_index).mod.single_threaded)
  variable_index.setThreadLocal(.generaldynamic, &o.builder);
  if (is_weak_linkage) variable_index.setLinkage(.extern_weak, &o.builder);
+ if (is_dll_import) variable_index.setDllStorageClass(.dllimport, &o.builder);
  } else {
  variable_index.setLinkage(.internal, &o.builder);
  variable_index.setUnnamedAddr(.unnamed_addr, &o.builder);
@@ -4782,10 +4783,10 @@ pub const NavGen = struct {
  const nav = ip.getNav(nav_index);
  const resolved = nav.status.resolved;
 
- const is_extern, const lib_name, const is_threadlocal, const is_weak_linkage, const is_const, const init_val, const owner_nav = switch (ip.indexToKey(resolved.val)) {
- .variable => |variable| .{ false, variable.lib_name, variable.is_threadlocal, variable.is_weak_linkage, false, variable.init, variable.owner_nav },
- .@"extern" => |@"extern"| .{ true, @"extern".lib_name, @"extern".is_threadlocal, @"extern".is_weak_linkage, @"extern".is_const, .none, @"extern".owner_nav },
- else => .{ false, .none, false, false, true, resolved.val, nav_index },
+ const is_extern, const lib_name, const is_threadlocal, const is_weak_linkage, const is_dll_import, const is_const, const init_val, const owner_nav = switch (ip.indexToKey(resolved.val)) {
+ .variable => |variable| .{ false, variable.lib_name, variable.is_threadlocal, variable.is_weak_linkage, false, false, variable.init, variable.owner_nav },
+ .@"extern" => |@"extern"| .{ true, @"extern".lib_name, @"extern".is_threadlocal, @"extern".is_weak_linkage, @"extern".is_dll_import, @"extern".is_const, .none, @"extern".owner_nav },
+ else => .{ false, .none, false, false, false, true, resolved.val, nav_index },
  };
  const ty = Type.fromInterned(nav.typeOf(ip));
 
@@ -4860,8 +4861,11 @@ pub const NavGen = struct {
  try global_index.rename(decl_name, &o.builder);
  global_index.setLinkage(.external, &o.builder);
  global_index.setUnnamedAddr(.default, &o.builder);
- if (zcu.comp.config.dll_export_fns)
+ if (is_dll_import) {
+ global_index.setDllStorageClass(.dllimport, &o.builder);
+ } else if (zcu.comp.config.dll_export_fns) {
  global_index.setDllStorageClass(.default, &o.builder);
+ }
 
  if (is_weak_linkage) global_index.setLinkage(.extern_weak, &o.builder);
  }

src/codegen/llvm/Builder.zig

@@ -2528,6 +2528,10 @@ pub const Variable = struct {
  return self.ptrConst(builder).global.setLinkage(linkage, builder);
  }
 
+ pub fn setDllStorageClass(self: Index, class: DllStorageClass, builder: *Builder) void {
+ return self.ptrConst(builder).global.setDllStorageClass(class, builder);
+ }
+
  pub fn setUnnamedAddr(self: Index, unnamed_addr: UnnamedAddr, builder: *Builder) void {
  return self.ptrConst(builder).global.setUnnamedAddr(unnamed_addr, builder);
  }

test/cases/compile_errors/builtin_extern_in_comptime_scope.zig

@@ -0,0 +1,18 @@
+const foo_tl = @extern(*i32, .{ .name = "foo", .is_thread_local = true });
+const foo_dll = @extern(*i32, .{ .name = "foo", .is_dll_import = true });
+pub export fn entry() void {
+ _ = foo_tl;
+}
+pub export fn entry2() void {
+ _ = foo_dll;
+}
+// error
+// backend=stage2
+// target=native
+//
+// :1:16: error: unable to resolve comptime value
+// :1:16: note: global variable initializer must be comptime-known
+// :1:16: note: thread local and dll imported variables have runtime-known addresses
+// :2:17: error: unable to resolve comptime value
+// :2:17: note: global variable initializer must be comptime-known
+// :2:17: note: thread local and dll imported variables have runtime-known addresses

test/standalone/extern/build.zig

@@ -1,6 +1,9 @@
 const std = @import("std");
 
 pub fn build(b: *std.Build) void {
+ const test_step = b.step("test", "Test it");
+ b.default_step = test_step;
+
  const optimize: std.builtin.OptimizeMode = .Debug;
 
  const obj = b.addObject(.{
@@ -9,12 +12,20 @@ pub fn build(b: *std.Build) void {
  .target = b.graph.host,
  .optimize = optimize,
  });
- const main = b.addTest(.{
+ const shared = b.addSharedLibrary(.{
+ .name = "shared",
+ .target = b.graph.host,
+ .optimize = optimize,
+ .link_libc = true,
+ });
+ if (b.graph.host.result.abi == .msvc) shared.defineCMacro("API", "__declspec(dllexport)");
+ shared.addCSourceFile(.{ .file = b.path("shared.c"), .flags = &.{} });
+ const test_exe = b.addTest(.{
  .root_source_file = b.path("main.zig"),
  .optimize = optimize,
  });
- main.addObject(obj);
+ test_exe.addObject(obj);
+ test_exe.linkLibrary(shared);
 
- const test_step = b.step("test", "Test it");
- test_step.dependOn(&main.step);
+ test_step.dependOn(&b.addRunArtifact(test_exe).step);
 }

test/standalone/extern/main.zig

@@ -1,4 +1,5 @@
 const assert = @import("std").debug.assert;
+const testing = @import("std").testing;
 
 const updateHidden = @extern(*const fn (u32) callconv(.C) void, .{ .name = "updateHidden" });
 const getHidden = @extern(*const fn () callconv(.C) u32, .{ .name = "getHidden" });
@@ -8,14 +9,18 @@ const T = extern struct { x: u32 };
 test {
  const mut_val_ptr = @extern(*f64, .{ .name = "mut_val" });
  const const_val_ptr = @extern(*const T, .{ .name = "const_val" });
+ const shared_val_ptr = @extern(*c_int, .{ .name = "shared_val", .is_dll_import = true });
 
  assert(getHidden() == 0);
  updateHidden(123);
  assert(getHidden() == 123);
-
  assert(mut_val_ptr.* == 1.23);
  mut_val_ptr.* = 10.0;
  assert(mut_val_ptr.* == 10.0);
 
  assert(const_val_ptr.x == 42);
+
+ assert(shared_val_ptr.* == 1234);
+ shared_val_ptr.* = 1235;
+ assert(shared_val_ptr.* == 1235);
 }

test/standalone/extern/shared.c

@@ -0,0 +1,5 @@
+#ifndef API
+#define API
+#endif
+
+API int shared_val = 1234;

lib/std/builtin.zig

@@ -683,6 +683,7 @@ pub const ExternOptions = struct {
  library_name: ?[]const u8 = null,
  linkage: GlobalLinkage = .strong,
  is_thread_local: bool = false,
+ is_dll_import: bool = false,
 };
 
 /// This data structure is used by the Zig language code generation and

src/InternPool.zig

@@ -2054,6 +2054,7 @@ pub const Key = union(enum) {
  is_const: bool,
  is_threadlocal: bool,
  is_weak_linkage: bool,
+ is_dll_import: bool,
  alignment: Alignment,
  @"addrspace": std.builtin.AddressSpace,
  /// The ZIR instruction which created this extern; used only for source locations.
@@ -2675,7 +2676,8 @@ pub const Key = union(enum) {
  asBytes(&e.ty) ++ asBytes(&e.lib_name) ++
  asBytes(&e.is_const) ++ asBytes(&e.is_threadlocal) ++
  asBytes(&e.is_weak_linkage) ++ asBytes(&e.alignment) ++
- asBytes(&e.@"addrspace") ++ asBytes(&e.zir_index)),
+ asBytes(&e.is_dll_import) ++ asBytes(&e.@"addrspace") ++
+ asBytes(&e.zir_index)),
  };
  }
 
@@ -2771,6 +2773,7 @@ pub const Key = union(enum) {
  a_info.is_const == b_info.is_const and
  a_info.is_threadlocal == b_info.is_threadlocal and
  a_info.is_weak_linkage == b_info.is_weak_linkage and
+ a_info.is_dll_import == b_info.is_dll_import and
  a_info.alignment == b_info.alignment and
  a_info.@"addrspace" == b_info.@"addrspace" and
  a_info.zir_index == b_info.zir_index;
@@ -5370,7 +5373,8 @@ pub const Tag = enum(u8) {
  is_const: bool,
  is_threadlocal: bool,
  is_weak_linkage: bool,
- _: u29 = 0,
+ is_dll_import: bool,
+ _: u28 = 0,
  };
  };
 
@@ -6715,6 +6719,7 @@ pub fn indexToKey(ip: *const InternPool, index: Index) Key {
  .is_const = extra.flags.is_const,
  .is_threadlocal = extra.flags.is_threadlocal,
  .is_weak_linkage = extra.flags.is_weak_linkage,
+ .is_dll_import = extra.flags.is_dll_import,
  .alignment = nav.status.resolved.alignment,
  .@"addrspace" = nav.status.resolved.@"addrspace",
  .zir_index = extra.zir_index,
@@ -7381,6 +7386,7 @@ pub fn get(ip: *InternPool, gpa: Allocator, tid: Zcu.PerThread.Id, key: Key) All
  .is_const = false,
  .is_threadlocal = variable.is_threadlocal,
  .is_weak_linkage = variable.is_weak_linkage,
+ .is_dll_import = false,
  },
  }),
  });
@@ -8644,6 +8650,7 @@ pub fn getExtern(
  .is_const = key.is_const,
  .is_threadlocal = key.is_threadlocal,
  .is_weak_linkage = key.is_weak_linkage,
+ .is_dll_import = key.is_dll_import,
  },
  .zir_index = key.zir_index,
  .owner_nav = owner_nav,

src/Sema.zig

@@ -876,6 +876,7 @@ const InferredAlloc = struct {
 
 const NeededComptimeReason = struct {
  needed_comptime_reason: []const u8,
+ value_comptime_reason: ?[]const u8 = null,
  block_comptime_reason: ?*const Block.ComptimeReason = null,
 };
 
@@ -2251,7 +2252,7 @@ fn resolveValueAllowVariables(sema: *Sema, inst: Air.Inst.Ref) CompileError!?Val
  }
  };
  const val = Value.fromInterned(ip_index);
- if (val.isPtrToThreadLocal(pt.zcu)) return null;
+ if (val.isPtrRuntimeValue(pt.zcu)) return null;
  return val;
 }
 
@@ -2277,8 +2278,14 @@ pub fn resolveFinalDeclValue(
  const zcu = sema.pt.zcu;
 
  const val = try sema.resolveValueAllowVariables(air_ref) orelse {
+ const value_comptime_reason: ?[]const u8 = if (air_ref.toInterned()) |_|
+ "thread local and dll imported variables have runtime-known addresses"
+ else
+ null;
+
  return sema.failWithNeededComptime(block, src, .{
  .needed_comptime_reason = "global variable initializer must be comptime-known",
+ .value_comptime_reason = value_comptime_reason,
  });
  };
  if (val.isGenericPoison()) return error.GenericPoison;
@@ -2296,6 +2303,9 @@ fn failWithNeededComptime(sema: *Sema, block: *Block, src: LazySrcLoc, reason: N
  const msg = try sema.errMsg(src, "unable to resolve comptime value", .{});
  errdefer msg.destroy(sema.gpa);
  try sema.errNote(src, msg, "{s}", .{reason.needed_comptime_reason});
+ if (reason.value_comptime_reason) |value_comptime_reason| {
+ try sema.errNote(src, msg, "{s}", .{value_comptime_reason});
+ }
 
  if (reason.block_comptime_reason) |block_comptime_reason| {
  try block_comptime_reason.explain(sema, msg);
@@ -9960,6 +9970,7 @@ fn funcCommon(
  .is_const = true,
  .is_threadlocal = false,
  .is_weak_linkage = false,
+ .is_dll_import = false,
  .alignment = alignment orelse .none,
  .@"addrspace" = address_space orelse .generic,
  .zir_index = sema.getOwnerCauDeclInst(), // `declaration` instruction
@@ -26505,6 +26516,7 @@ fn zirVarExtended(
  .is_const = small.is_const,
  .is_threadlocal = small.is_threadlocal,
  .is_weak_linkage = false,
+ .is_dll_import = false,
  .alignment = alignment,
  .@"addrspace" = @"addrspace",
  .zir_index = sema.getOwnerCauDeclInst(), // `declaration` instruction
@@ -26958,6 +26970,7 @@ fn resolveExternOptions(
  library_name: InternPool.OptionalNullTerminatedString = .none,
  linkage: std.builtin.GlobalLinkage = .strong,
  is_thread_local: bool = false,
+ is_dll_import: bool = false,
 } {
  const pt = sema.pt;
  const zcu = pt.zcu;
@@ -26971,6 +26984,7 @@ fn resolveExternOptions(
  const library_src = block.src(.{ .init_field_library = src.offset.node_offset_builtin_call_arg.builtin_call_node });
  const linkage_src = block.src(.{ .init_field_linkage = src.offset.node_offset_builtin_call_arg.builtin_call_node });
  const thread_local_src = block.src(.{ .init_field_thread_local = src.offset.node_offset_builtin_call_arg.builtin_call_node });
+ const dll_import_src = block.src(.{ .init_field_dll_import = src.offset.node_offset_builtin_call_arg.builtin_call_node });
 
  const name_ref = try sema.fieldVal(block, src, options, try ip.getOrPutString(gpa, pt.tid, "name", .no_embedded_nulls), name_src);
  const name = try sema.toConstString(block, name_src, name_ref, .{
@@ -27004,6 +27018,11 @@ fn resolveExternOptions(
  break :library_name library_name;
  } else null;
 
+ const is_dll_import_ref = try sema.fieldVal(block, src, options, try ip.getOrPutString(gpa, pt.tid, "is_dll_import", .no_embedded_nulls), dll_import_src);
+ const is_dll_import_val = try sema.resolveConstDefinedValue(block, dll_import_src, is_dll_import_ref, .{
+ .needed_comptime_reason = "it must be comptime-known if the symbol is imported from a dll",
+ });
+
  if (name.len == 0) {
  return sema.fail(block, name_src, "extern symbol name cannot be empty", .{});
  }
@@ -27017,6 +27036,7 @@ fn resolveExternOptions(
  .library_name = try ip.getOrPutStringOpt(gpa, pt.tid, library_name, .no_embedded_nulls),
  .linkage = linkage,
  .is_thread_local = is_thread_local_val.toBool(),
+ .is_dll_import = is_dll_import_val.toBool(),
  };
 }
 
@@ -27062,6 +27082,7 @@ fn zirBuiltinExtern(
  .is_const = ptr_info.flags.is_const,
  .is_threadlocal = options.is_thread_local,
  .is_weak_linkage = options.linkage == .weak,
+ .is_dll_import = options.is_dll_import,
  .alignment = ptr_info.flags.alignment,
  .@"addrspace" = ptr_info.flags.address_space,
  // This instruction is just for source locations.

src/Value.zig

@@ -1340,11 +1340,11 @@ pub fn isLazySize(val: Value, zcu: *Zcu) bool {
  };
 }
 
-pub fn isPtrToThreadLocal(val: Value, zcu: *Zcu) bool {
+pub fn isPtrRuntimeValue(val: Value, zcu: *Zcu) bool {
  const ip = &zcu.intern_pool;
  const nav = ip.getBackingNav(val.toIntern()).unwrap() orelse return false;
  return switch (ip.indexToKey(ip.getNav(nav).status.resolved.val)) {
- .@"extern" => |e| e.is_threadlocal,
+ .@"extern" => |e| e.is_threadlocal or e.is_dll_import,
  .variable => |v| v.is_threadlocal,
  else => false,
  };

src/Zcu.zig

@@ -1522,6 +1522,7 @@ pub const SrcLoc = struct {
  .init_field_cache,
  .init_field_library,
  .init_field_thread_local,
+ .init_field_dll_import,
  => |builtin_call_node| {
  const wanted = switch (src_loc.lazy) {
  .init_field_name => "name",
@@ -1533,6 +1534,7 @@ pub const SrcLoc = struct {
  .init_field_cache => "cache",
  .init_field_library => "library",
  .init_field_thread_local => "thread_local",
+ .init_field_dll_import => "dll_import",
  else => unreachable,
  };
  const tree = try src_loc.file_scope.getTree(gpa);
@@ -1959,6 +1961,7 @@ pub const LazySrcLoc = struct {
  init_field_cache: i32,
  init_field_library: i32,
  init_field_thread_local: i32,
+ init_field_dll_import: i32,
  /// The source location points to the value of an item in a specific
  /// case of a `switch`.
  switch_case_item: SwitchItem,

src/Zcu/PerThread.zig

@@ -2763,6 +2763,7 @@ pub fn getCoerced(pt: Zcu.PerThread, val: Value, new_ty: Type) Allocator.Error!V
  .is_const = e.is_const,
  .is_threadlocal = e.is_threadlocal,
  .is_weak_linkage = e.is_weak_linkage,
+ .is_dll_import = e.is_dll_import,
  .alignment = e.alignment,
  .@"addrspace" = e.@"addrspace",
  .zir_index = e.zir_index,

src/codegen/llvm.zig

@@ -3237,10 +3237,10 @@ pub const Object = struct {
  const ip = &zcu.intern_pool;
  const nav = ip.getNav(nav_index);
  const resolved = nav.status.resolved;
- const is_extern, const is_threadlocal, const is_weak_linkage = switch (ip.indexToKey(resolved.val)) {
- .variable => |variable| .{ false, variable.is_threadlocal, variable.is_weak_linkage },
- .@"extern" => |@"extern"| .{ true, @"extern".is_threadlocal, @"extern".is_weak_linkage },
- else => .{ false, false, false },
+ const is_extern, const is_threadlocal, const is_weak_linkage, const is_dll_import = switch (ip.indexToKey(resolved.val)) {
+ .variable => |variable| .{ false, variable.is_threadlocal, variable.is_weak_linkage, false },
+ .@"extern" => |@"extern"| .{ true, @"extern".is_threadlocal, @"extern".is_weak_linkage, @"extern".is_dll_import },
+ else => .{ false, false, false, false },
  };
 
  const variable_index = try o.builder.addVariable(
@@ -3257,6 +3257,7 @@ pub const Object = struct {
  if (is_threadlocal and !zcu.navFileScope(nav_index).mod.single_threaded)
  variable_index.setThreadLocal(.generaldynamic, &o.builder);
  if (is_weak_linkage) variable_index.setLinkage(.extern_weak, &o.builder);
+ if (is_dll_import) variable_index.setDllStorageClass(.dllimport, &o.builder);
  } else {
  variable_index.setLinkage(.internal, &o.builder);
  variable_index.setUnnamedAddr(.unnamed_addr, &o.builder);
@@ -4782,10 +4783,10 @@ pub const NavGen = struct {
  const nav = ip.getNav(nav_index);
  const resolved = nav.status.resolved;
 
- const is_extern, const lib_name, const is_threadlocal, const is_weak_linkage, const is_const, const init_val, const owner_nav = switch (ip.indexToKey(resolved.val)) {
- .variable => |variable| .{ false, variable.lib_name, variable.is_threadlocal, variable.is_weak_linkage, false, variable.init, variable.owner_nav },
- .@"extern" => |@"extern"| .{ true, @"extern".lib_name, @"extern".is_threadlocal, @"extern".is_weak_linkage, @"extern".is_const, .none, @"extern".owner_nav },
- else => .{ false, .none, false, false, true, resolved.val, nav_index },
+ const is_extern, const lib_name, const is_threadlocal, const is_weak_linkage, const is_dll_import, const is_const, const init_val, const owner_nav = switch (ip.indexToKey(resolved.val)) {
+ .variable => |variable| .{ false, variable.lib_name, variable.is_threadlocal, variable.is_weak_linkage, false, false, variable.init, variable.owner_nav },
+ .@"extern" => |@"extern"| .{ true, @"extern".lib_name, @"extern".is_threadlocal, @"extern".is_weak_linkage, @"extern".is_dll_import, @"extern".is_const, .none, @"extern".owner_nav },
+ else => .{ false, .none, false, false, false, true, resolved.val, nav_index },
  };
  const ty = Type.fromInterned(nav.typeOf(ip));
 
@@ -4860,8 +4861,11 @@ pub const NavGen = struct {
  try global_index.rename(decl_name, &o.builder);
  global_index.setLinkage(.external, &o.builder);
  global_index.setUnnamedAddr(.default, &o.builder);
- if (zcu.comp.config.dll_export_fns)
+ if (is_dll_import) {
+ global_index.setDllStorageClass(.dllimport, &o.builder);
+ } else if (zcu.comp.config.dll_export_fns) {
  global_index.setDllStorageClass(.default, &o.builder);
+ }
 
  if (is_weak_linkage) global_index.setLinkage(.extern_weak, &o.builder);
  }

src/codegen/llvm/Builder.zig

@@ -2528,6 +2528,10 @@ pub const Variable = struct {
  return self.ptrConst(builder).global.setLinkage(linkage, builder);
  }
 
+ pub fn setDllStorageClass(self: Index, class: DllStorageClass, builder: *Builder) void {
+ return self.ptrConst(builder).global.setDllStorageClass(class, builder);
+ }
+
  pub fn setUnnamedAddr(self: Index, unnamed_addr: UnnamedAddr, builder: *Builder) void {
  return self.ptrConst(builder).global.setUnnamedAddr(unnamed_addr, builder);
  }

test/cases/compile_errors/builtin_extern_in_comptime_scope.zig

@@ -0,0 +1,18 @@
+const foo_tl = @extern(*i32, .{ .name = "foo", .is_thread_local = true });
+const foo_dll = @extern(*i32, .{ .name = "foo", .is_dll_import = true });
+pub export fn entry() void {
+ _ = foo_tl;
+}
+pub export fn entry2() void {
+ _ = foo_dll;
+}
+// error
+// backend=stage2
+// target=native
+//
+// :1:16: error: unable to resolve comptime value
+// :1:16: note: global variable initializer must be comptime-known
+// :1:16: note: thread local and dll imported variables have runtime-known addresses
+// :2:17: error: unable to resolve comptime value
+// :2:17: note: global variable initializer must be comptime-known
+// :2:17: note: thread local and dll imported variables have runtime-known addresses

test/standalone/extern/build.zig

@@ -1,6 +1,9 @@
 const std = @import("std");
 
 pub fn build(b: *std.Build) void {
+ const test_step = b.step("test", "Test it");
+ b.default_step = test_step;
+
  const optimize: std.builtin.OptimizeMode = .Debug;
 
  const obj = b.addObject(.{
@@ -9,12 +12,20 @@ pub fn build(b: *std.Build) void {
  .target = b.graph.host,
  .optimize = optimize,
  });
- const main = b.addTest(.{
+ const shared = b.addSharedLibrary(.{
+ .name = "shared",
+ .target = b.graph.host,
+ .optimize = optimize,
+ .link_libc = true,
+ });
+ if (b.graph.host.result.abi == .msvc) shared.defineCMacro("API", "__declspec(dllexport)");
+ shared.addCSourceFile(.{ .file = b.path("shared.c"), .flags = &.{} });
+ const test_exe = b.addTest(.{
  .root_source_file = b.path("main.zig"),
  .optimize = optimize,
  });
- main.addObject(obj);
+ test_exe.addObject(obj);
+ test_exe.linkLibrary(shared);
 
- const test_step = b.step("test", "Test it");
- test_step.dependOn(&main.step);
+ test_step.dependOn(&b.addRunArtifact(test_exe).step);
 }

test/standalone/extern/main.zig

@@ -1,4 +1,5 @@
 const assert = @import("std").debug.assert;
+const testing = @import("std").testing;
 
 const updateHidden = @extern(*const fn (u32) callconv(.C) void, .{ .name = "updateHidden" });
 const getHidden = @extern(*const fn () callconv(.C) u32, .{ .name = "getHidden" });
@@ -8,14 +9,18 @@ const T = extern struct { x: u32 };
 test {
  const mut_val_ptr = @extern(*f64, .{ .name = "mut_val" });
  const const_val_ptr = @extern(*const T, .{ .name = "const_val" });
+ const shared_val_ptr = @extern(*c_int, .{ .name = "shared_val", .is_dll_import = true });
 
  assert(getHidden() == 0);
  updateHidden(123);
  assert(getHidden() == 123);
-
  assert(mut_val_ptr.* == 1.23);
  mut_val_ptr.* = 10.0;
  assert(mut_val_ptr.* == 10.0);
 
  assert(const_val_ptr.x == 42);
+
+ assert(shared_val_ptr.* == 1234);
+ shared_val_ptr.* = 1235;
+ assert(shared_val_ptr.* == 1235);
 }

test/standalone/extern/shared.c

@@ -0,0 +1,5 @@
+#ifndef API
+#define API
+#endif
+
+API int shared_val = 1234;

lib/std/builtin.zig

@@ -683,6 +683,7 @@ pub const ExternOptions = struct {
  library_name: ?[]const u8 = null,
  linkage: GlobalLinkage = .strong,
  is_thread_local: bool = false,
+ is_dll_import: bool = false,
 };
 
 /// This data structure is used by the Zig language code generation and

src/InternPool.zig

@@ -2054,6 +2054,7 @@ pub const Key = union(enum) {
  is_const: bool,
  is_threadlocal: bool,
  is_weak_linkage: bool,
+ is_dll_import: bool,
  alignment: Alignment,
  @"addrspace": std.builtin.AddressSpace,
  /// The ZIR instruction which created this extern; used only for source locations.
@@ -2675,7 +2676,8 @@ pub const Key = union(enum) {
  asBytes(&e.ty) ++ asBytes(&e.lib_name) ++
  asBytes(&e.is_const) ++ asBytes(&e.is_threadlocal) ++
  asBytes(&e.is_weak_linkage) ++ asBytes(&e.alignment) ++
- asBytes(&e.@"addrspace") ++ asBytes(&e.zir_index)),
+ asBytes(&e.is_dll_import) ++ asBytes(&e.@"addrspace") ++
+ asBytes(&e.zir_index)),
  };
  }
 
@@ -2771,6 +2773,7 @@ pub const Key = union(enum) {
  a_info.is_const == b_info.is_const and
  a_info.is_threadlocal == b_info.is_threadlocal and
  a_info.is_weak_linkage == b_info.is_weak_linkage and
+ a_info.is_dll_import == b_info.is_dll_import and
  a_info.alignment == b_info.alignment and
  a_info.@"addrspace" == b_info.@"addrspace" and
  a_info.zir_index == b_info.zir_index;
@@ -5370,7 +5373,8 @@ pub const Tag = enum(u8) {
  is_const: bool,
  is_threadlocal: bool,
  is_weak_linkage: bool,
- _: u29 = 0,
+ is_dll_import: bool,
+ _: u28 = 0,
  };
  };
 
@@ -6715,6 +6719,7 @@ pub fn indexToKey(ip: *const InternPool, index: Index) Key {
  .is_const = extra.flags.is_const,
  .is_threadlocal = extra.flags.is_threadlocal,
  .is_weak_linkage = extra.flags.is_weak_linkage,
+ .is_dll_import = extra.flags.is_dll_import,
  .alignment = nav.status.resolved.alignment,
  .@"addrspace" = nav.status.resolved.@"addrspace",
  .zir_index = extra.zir_index,
@@ -7381,6 +7386,7 @@ pub fn get(ip: *InternPool, gpa: Allocator, tid: Zcu.PerThread.Id, key: Key) All
  .is_const = false,
  .is_threadlocal = variable.is_threadlocal,
  .is_weak_linkage = variable.is_weak_linkage,
+ .is_dll_import = false,
  },
  }),
  });
@@ -8644,6 +8650,7 @@ pub fn getExtern(
  .is_const = key.is_const,
  .is_threadlocal = key.is_threadlocal,
  .is_weak_linkage = key.is_weak_linkage,
+ .is_dll_import = key.is_dll_import,
  },
  .zir_index = key.zir_index,
  .owner_nav = owner_nav,

src/Sema.zig

@@ -876,6 +876,7 @@ const InferredAlloc = struct {
 
 const NeededComptimeReason = struct {
  needed_comptime_reason: []const u8,
+ value_comptime_reason: ?[]const u8 = null,
  block_comptime_reason: ?*const Block.ComptimeReason = null,
 };
 
@@ -2251,7 +2252,7 @@ fn resolveValueAllowVariables(sema: *Sema, inst: Air.Inst.Ref) CompileError!?Val
  }
  };
  const val = Value.fromInterned(ip_index);
- if (val.isPtrToThreadLocal(pt.zcu)) return null;
+ if (val.isPtrRuntimeValue(pt.zcu)) return null;
  return val;
 }
 
@@ -2277,8 +2278,14 @@ pub fn resolveFinalDeclValue(
  const zcu = sema.pt.zcu;
 
  const val = try sema.resolveValueAllowVariables(air_ref) orelse {
+ const value_comptime_reason: ?[]const u8 = if (air_ref.toInterned()) |_|
+ "thread local and dll imported variables have runtime-known addresses"
+ else
+ null;
+
  return sema.failWithNeededComptime(block, src, .{
  .needed_comptime_reason = "global variable initializer must be comptime-known",
+ .value_comptime_reason = value_comptime_reason,
  });
  };
  if (val.isGenericPoison()) return error.GenericPoison;
@@ -2296,6 +2303,9 @@ fn failWithNeededComptime(sema: *Sema, block: *Block, src: LazySrcLoc, reason: N
  const msg = try sema.errMsg(src, "unable to resolve comptime value", .{});
  errdefer msg.destroy(sema.gpa);
  try sema.errNote(src, msg, "{s}", .{reason.needed_comptime_reason});
+ if (reason.value_comptime_reason) |value_comptime_reason| {
+ try sema.errNote(src, msg, "{s}", .{value_comptime_reason});
+ }
 
  if (reason.block_comptime_reason) |block_comptime_reason| {
  try block_comptime_reason.explain(sema, msg);
@@ -9960,6 +9970,7 @@ fn funcCommon(
  .is_const = true,
  .is_threadlocal = false,
  .is_weak_linkage = false,
+ .is_dll_import = false,
  .alignment = alignment orelse .none,
  .@"addrspace" = address_space orelse .generic,
  .zir_index = sema.getOwnerCauDeclInst(), // `declaration` instruction
@@ -26505,6 +26516,7 @@ fn zirVarExtended(
  .is_const = small.is_const,
  .is_threadlocal = small.is_threadlocal,
  .is_weak_linkage = false,
+ .is_dll_import = false,
  .alignment = alignment,
  .@"addrspace" = @"addrspace",
  .zir_index = sema.getOwnerCauDeclInst(), // `declaration` instruction
@@ -26958,6 +26970,7 @@ fn resolveExternOptions(
  library_name: InternPool.OptionalNullTerminatedString = .none,
  linkage: std.builtin.GlobalLinkage = .strong,
  is_thread_local: bool = false,
+ is_dll_import: bool = false,
 } {
  const pt = sema.pt;
  const zcu = pt.zcu;
@@ -26971,6 +26984,7 @@ fn resolveExternOptions(
  const library_src = block.src(.{ .init_field_library = src.offset.node_offset_builtin_call_arg.builtin_call_node });
  const linkage_src = block.src(.{ .init_field_linkage = src.offset.node_offset_builtin_call_arg.builtin_call_node });
  const thread_local_src = block.src(.{ .init_field_thread_local = src.offset.node_offset_builtin_call_arg.builtin_call_node });
+ const dll_import_src = block.src(.{ .init_field_dll_import = src.offset.node_offset_builtin_call_arg.builtin_call_node });
 
  const name_ref = try sema.fieldVal(block, src, options, try ip.getOrPutString(gpa, pt.tid, "name", .no_embedded_nulls), name_src);
  const name = try sema.toConstString(block, name_src, name_ref, .{
@@ -27004,6 +27018,11 @@ fn resolveExternOptions(
  break :library_name library_name;
  } else null;
 
+ const is_dll_import_ref = try sema.fieldVal(block, src, options, try ip.getOrPutString(gpa, pt.tid, "is_dll_import", .no_embedded_nulls), dll_import_src);
+ const is_dll_import_val = try sema.resolveConstDefinedValue(block, dll_import_src, is_dll_import_ref, .{
+ .needed_comptime_reason = "it must be comptime-known if the symbol is imported from a dll",
+ });
+
  if (name.len == 0) {
  return sema.fail(block, name_src, "extern symbol name cannot be empty", .{});
  }
@@ -27017,6 +27036,7 @@ fn resolveExternOptions(
  .library_name = try ip.getOrPutStringOpt(gpa, pt.tid, library_name, .no_embedded_nulls),
  .linkage = linkage,
  .is_thread_local = is_thread_local_val.toBool(),
+ .is_dll_import = is_dll_import_val.toBool(),
  };
 }
 
@@ -27062,6 +27082,7 @@ fn zirBuiltinExtern(
  .is_const = ptr_info.flags.is_const,
  .is_threadlocal = options.is_thread_local,
  .is_weak_linkage = options.linkage == .weak,
+ .is_dll_import = options.is_dll_import,
  .alignment = ptr_info.flags.alignment,
  .@"addrspace" = ptr_info.flags.address_space,
  // This instruction is just for source locations.

src/Value.zig

@@ -1340,11 +1340,11 @@ pub fn isLazySize(val: Value, zcu: *Zcu) bool {
  };
 }
 
-pub fn isPtrToThreadLocal(val: Value, zcu: *Zcu) bool {
+pub fn isPtrRuntimeValue(val: Value, zcu: *Zcu) bool {
  const ip = &zcu.intern_pool;
  const nav = ip.getBackingNav(val.toIntern()).unwrap() orelse return false;
  return switch (ip.indexToKey(ip.getNav(nav).status.resolved.val)) {
- .@"extern" => |e| e.is_threadlocal,
+ .@"extern" => |e| e.is_threadlocal or e.is_dll_import,
  .variable => |v| v.is_threadlocal,
  else => false,
  };

src/Zcu.zig

@@ -1522,6 +1522,7 @@ pub const SrcLoc = struct {
  .init_field_cache,
  .init_field_library,
  .init_field_thread_local,
+ .init_field_dll_import,
  => |builtin_call_node| {
  const wanted = switch (src_loc.lazy) {
  .init_field_name => "name",
@@ -1533,6 +1534,7 @@ pub const SrcLoc = struct {
  .init_field_cache => "cache",
  .init_field_library => "library",
  .init_field_thread_local => "thread_local",
+ .init_field_dll_import => "dll_import",
  else => unreachable,
  };
  const tree = try src_loc.file_scope.getTree(gpa);
@@ -1959,6 +1961,7 @@ pub const LazySrcLoc = struct {
  init_field_cache: i32,
  init_field_library: i32,
  init_field_thread_local: i32,
+ init_field_dll_import: i32,
  /// The source location points to the value of an item in a specific
  /// case of a `switch`.
  switch_case_item: SwitchItem,

src/Zcu/PerThread.zig

@@ -2763,6 +2763,7 @@ pub fn getCoerced(pt: Zcu.PerThread, val: Value, new_ty: Type) Allocator.Error!V
  .is_const = e.is_const,
  .is_threadlocal = e.is_threadlocal,
  .is_weak_linkage = e.is_weak_linkage,
+ .is_dll_import = e.is_dll_import,
  .alignment = e.alignment,
  .@"addrspace" = e.@"addrspace",
  .zir_index = e.zir_index,

src/codegen/llvm.zig

@@ -3237,10 +3237,10 @@ pub const Object = struct {
  const ip = &zcu.intern_pool;
  const nav = ip.getNav(nav_index);
  const resolved = nav.status.resolved;
- const is_extern, const is_threadlocal, const is_weak_linkage = switch (ip.indexToKey(resolved.val)) {
- .variable => |variable| .{ false, variable.is_threadlocal, variable.is_weak_linkage },
- .@"extern" => |@"extern"| .{ true, @"extern".is_threadlocal, @"extern".is_weak_linkage },
- else => .{ false, false, false },
+ const is_extern, const is_threadlocal, const is_weak_linkage, const is_dll_import = switch (ip.indexToKey(resolved.val)) {
+ .variable => |variable| .{ false, variable.is_threadlocal, variable.is_weak_linkage, false },
+ .@"extern" => |@"extern"| .{ true, @"extern".is_threadlocal, @"extern".is_weak_linkage, @"extern".is_dll_import },
+ else => .{ false, false, false, false },
  };
 
  const variable_index = try o.builder.addVariable(
@@ -3257,6 +3257,7 @@ pub const Object = struct {
  if (is_threadlocal and !zcu.navFileScope(nav_index).mod.single_threaded)
  variable_index.setThreadLocal(.generaldynamic, &o.builder);
  if (is_weak_linkage) variable_index.setLinkage(.extern_weak, &o.builder);
+ if (is_dll_import) variable_index.setDllStorageClass(.dllimport, &o.builder);
  } else {
  variable_index.setLinkage(.internal, &o.builder);
  variable_index.setUnnamedAddr(.unnamed_addr, &o.builder);
@@ -4782,10 +4783,10 @@ pub const NavGen = struct {
  const nav = ip.getNav(nav_index);
  const resolved = nav.status.resolved;
 
- const is_extern, const lib_name, const is_threadlocal, const is_weak_linkage, const is_const, const init_val, const owner_nav = switch (ip.indexToKey(resolved.val)) {
- .variable => |variable| .{ false, variable.lib_name, variable.is_threadlocal, variable.is_weak_linkage, false, variable.init, variable.owner_nav },
- .@"extern" => |@"extern"| .{ true, @"extern".lib_name, @"extern".is_threadlocal, @"extern".is_weak_linkage, @"extern".is_const, .none, @"extern".owner_nav },
- else => .{ false, .none, false, false, true, resolved.val, nav_index },
+ const is_extern, const lib_name, const is_threadlocal, const is_weak_linkage, const is_dll_import, const is_const, const init_val, const owner_nav = switch (ip.indexToKey(resolved.val)) {
+ .variable => |variable| .{ false, variable.lib_name, variable.is_threadlocal, variable.is_weak_linkage, false, false, variable.init, variable.owner_nav },
+ .@"extern" => |@"extern"| .{ true, @"extern".lib_name, @"extern".is_threadlocal, @"extern".is_weak_linkage, @"extern".is_dll_import, @"extern".is_const, .none, @"extern".owner_nav },
+ else => .{ false, .none, false, false, false, true, resolved.val, nav_index },
  };
  const ty = Type.fromInterned(nav.typeOf(ip));
 
@@ -4860,8 +4861,11 @@ pub const NavGen = struct {
  try global_index.rename(decl_name, &o.builder);
  global_index.setLinkage(.external, &o.builder);
  global_index.setUnnamedAddr(.default, &o.builder);
- if (zcu.comp.config.dll_export_fns)
+ if (is_dll_import) {
+ global_index.setDllStorageClass(.dllimport, &o.builder);
+ } else if (zcu.comp.config.dll_export_fns) {
  global_index.setDllStorageClass(.default, &o.builder);
+ }
 
  if (is_weak_linkage) global_index.setLinkage(.extern_weak, &o.builder);
  }

src/codegen/llvm/Builder.zig

@@ -2528,6 +2528,10 @@ pub const Variable = struct {
  return self.ptrConst(builder).global.setLinkage(linkage, builder);
  }
 
+ pub fn setDllStorageClass(self: Index, class: DllStorageClass, builder: *Builder) void {
+ return self.ptrConst(builder).global.setDllStorageClass(class, builder);
+ }
+
  pub fn setUnnamedAddr(self: Index, unnamed_addr: UnnamedAddr, builder: *Builder) void {
  return self.ptrConst(builder).global.setUnnamedAddr(unnamed_addr, builder);
  }

test/cases/compile_errors/builtin_extern_in_comptime_scope.zig

@@ -0,0 +1,18 @@
+const foo_tl = @extern(*i32, .{ .name = "foo", .is_thread_local = true });
+const foo_dll = @extern(*i32, .{ .name = "foo", .is_dll_import = true });
+pub export fn entry() void {
+ _ = foo_tl;
+}
+pub export fn entry2() void {
+ _ = foo_dll;
+}
+// error
+// backend=stage2
+// target=native
+//
+// :1:16: error: unable to resolve comptime value
+// :1:16: note: global variable initializer must be comptime-known
+// :1:16: note: thread local and dll imported variables have runtime-known addresses
+// :2:17: error: unable to resolve comptime value
+// :2:17: note: global variable initializer must be comptime-known
+// :2:17: note: thread local and dll imported variables have runtime-known addresses

test/standalone/extern/build.zig

@@ -1,6 +1,9 @@
 const std = @import("std");
 
 pub fn build(b: *std.Build) void {
+ const test_step = b.step("test", "Test it");
+ b.default_step = test_step;
+
  const optimize: std.builtin.OptimizeMode = .Debug;
 
  const obj = b.addObject(.{
@@ -9,12 +12,20 @@ pub fn build(b: *std.Build) void {
  .target = b.graph.host,
  .optimize = optimize,
  });
- const main = b.addTest(.{
+ const shared = b.addSharedLibrary(.{
+ .name = "shared",
+ .target = b.graph.host,
+ .optimize = optimize,
+ .link_libc = true,
+ });
+ if (b.graph.host.result.abi == .msvc) shared.defineCMacro("API", "__declspec(dllexport)");
+ shared.addCSourceFile(.{ .file = b.path("shared.c"), .flags = &.{} });
+ const test_exe = b.addTest(.{
  .root_source_file = b.path("main.zig"),
  .optimize = optimize,
  });
- main.addObject(obj);
+ test_exe.addObject(obj);
+ test_exe.linkLibrary(shared);
 
- const test_step = b.step("test", "Test it");
- test_step.dependOn(&main.step);
+ test_step.dependOn(&b.addRunArtifact(test_exe).step);
 }

test/standalone/extern/main.zig

@@ -1,4 +1,5 @@
 const assert = @import("std").debug.assert;
+const testing = @import("std").testing;
 
 const updateHidden = @extern(*const fn (u32) callconv(.C) void, .{ .name = "updateHidden" });
 const getHidden = @extern(*const fn () callconv(.C) u32, .{ .name = "getHidden" });
@@ -8,14 +9,18 @@ const T = extern struct { x: u32 };
 test {
  const mut_val_ptr = @extern(*f64, .{ .name = "mut_val" });
  const const_val_ptr = @extern(*const T, .{ .name = "const_val" });
+ const shared_val_ptr = @extern(*c_int, .{ .name = "shared_val", .is_dll_import = true });
 
  assert(getHidden() == 0);
  updateHidden(123);
  assert(getHidden() == 123);
-
  assert(mut_val_ptr.* == 1.23);
  mut_val_ptr.* = 10.0;
  assert(mut_val_ptr.* == 10.0);
 
  assert(const_val_ptr.x == 42);
+
+ assert(shared_val_ptr.* == 1234);
+ shared_val_ptr.* = 1235;
+ assert(shared_val_ptr.* == 1235);
 }

test/standalone/extern/shared.c

@@ -0,0 +1,5 @@
+#ifndef API
+#define API
+#endif
+
+API int shared_val = 1234;

lib/std/builtin.zig

@@ -683,6 +683,7 @@ pub const ExternOptions = struct {
  library_name: ?[]const u8 = null,
  linkage: GlobalLinkage = .strong,
  is_thread_local: bool = false,
+ is_dll_import: bool = false,
 };
 
 /// This data structure is used by the Zig language code generation and

src/InternPool.zig

@@ -2054,6 +2054,7 @@ pub const Key = union(enum) {
  is_const: bool,
  is_threadlocal: bool,
  is_weak_linkage: bool,
+ is_dll_import: bool,
  alignment: Alignment,
  @"addrspace": std.builtin.AddressSpace,
  /// The ZIR instruction which created this extern; used only for source locations.
@@ -2675,7 +2676,8 @@ pub const Key = union(enum) {
  asBytes(&e.ty) ++ asBytes(&e.lib_name) ++
  asBytes(&e.is_const) ++ asBytes(&e.is_threadlocal) ++
  asBytes(&e.is_weak_linkage) ++ asBytes(&e.alignment) ++
- asBytes(&e.@"addrspace") ++ asBytes(&e.zir_index)),
+ asBytes(&e.is_dll_import) ++ asBytes(&e.@"addrspace") ++
+ asBytes(&e.zir_index)),
  };
  }
 
@@ -2771,6 +2773,7 @@ pub const Key = union(enum) {
  a_info.is_const == b_info.is_const and
  a_info.is_threadlocal == b_info.is_threadlocal and
  a_info.is_weak_linkage == b_info.is_weak_linkage and
+ a_info.is_dll_import == b_info.is_dll_import and
  a_info.alignment == b_info.alignment and
  a_info.@"addrspace" == b_info.@"addrspace" and
  a_info.zir_index == b_info.zir_index;
@@ -5370,7 +5373,8 @@ pub const Tag = enum(u8) {
  is_const: bool,
  is_threadlocal: bool,
  is_weak_linkage: bool,
- _: u29 = 0,
+ is_dll_import: bool,
+ _: u28 = 0,
  };
  };
 
@@ -6715,6 +6719,7 @@ pub fn indexToKey(ip: *const InternPool, index: Index) Key {
  .is_const = extra.flags.is_const,
  .is_threadlocal = extra.flags.is_threadlocal,
  .is_weak_linkage = extra.flags.is_weak_linkage,
+ .is_dll_import = extra.flags.is_dll_import,
  .alignment = nav.status.resolved.alignment,
  .@"addrspace" = nav.status.resolved.@"addrspace",
  .zir_index = extra.zir_index,
@@ -7381,6 +7386,7 @@ pub fn get(ip: *InternPool, gpa: Allocator, tid: Zcu.PerThread.Id, key: Key) All
  .is_const = false,
  .is_threadlocal = variable.is_threadlocal,
  .is_weak_linkage = variable.is_weak_linkage,
+ .is_dll_import = false,
  },
  }),
  });
@@ -8644,6 +8650,7 @@ pub fn getExtern(
  .is_const = key.is_const,
  .is_threadlocal = key.is_threadlocal,
  .is_weak_linkage = key.is_weak_linkage,
+ .is_dll_import = key.is_dll_import,
  },
  .zir_index = key.zir_index,
  .owner_nav = owner_nav,

src/Sema.zig

@@ -876,6 +876,7 @@ const InferredAlloc = struct {
 
 const NeededComptimeReason = struct {
  needed_comptime_reason: []const u8,
+ value_comptime_reason: ?[]const u8 = null,
  block_comptime_reason: ?*const Block.ComptimeReason = null,
 };
 
@@ -2251,7 +2252,7 @@ fn resolveValueAllowVariables(sema: *Sema, inst: Air.Inst.Ref) CompileError!?Val
  }
  };
  const val = Value.fromInterned(ip_index);
- if (val.isPtrToThreadLocal(pt.zcu)) return null;
+ if (val.isPtrRuntimeValue(pt.zcu)) return null;
  return val;
 }
 
@@ -2277,8 +2278,14 @@ pub fn resolveFinalDeclValue(
  const zcu = sema.pt.zcu;
 
  const val = try sema.resolveValueAllowVariables(air_ref) orelse {
+ const value_comptime_reason: ?[]const u8 = if (air_ref.toInterned()) |_|
+ "thread local and dll imported variables have runtime-known addresses"
+ else
+ null;
+
  return sema.failWithNeededComptime(block, src, .{
  .needed_comptime_reason = "global variable initializer must be comptime-known",
+ .value_comptime_reason = value_comptime_reason,
  });
  };
  if (val.isGenericPoison()) return error.GenericPoison;
@@ -2296,6 +2303,9 @@ fn failWithNeededComptime(sema: *Sema, block: *Block, src: LazySrcLoc, reason: N
  const msg = try sema.errMsg(src, "unable to resolve comptime value", .{});
  errdefer msg.destroy(sema.gpa);
  try sema.errNote(src, msg, "{s}", .{reason.needed_comptime_reason});
+ if (reason.value_comptime_reason) |value_comptime_reason| {
+ try sema.errNote(src, msg, "{s}", .{value_comptime_reason});
+ }
 
  if (reason.block_comptime_reason) |block_comptime_reason| {
  try block_comptime_reason.explain(sema, msg);
@@ -9960,6 +9970,7 @@ fn funcCommon(
  .is_const = true,
  .is_threadlocal = false,
  .is_weak_linkage = false,
+ .is_dll_import = false,
  .alignment = alignment orelse .none,
  .@"addrspace" = address_space orelse .generic,
  .zir_index = sema.getOwnerCauDeclInst(), // `declaration` instruction
@@ -26505,6 +26516,7 @@ fn zirVarExtended(
  .is_const = small.is_const,
  .is_threadlocal = small.is_threadlocal,
  .is_weak_linkage = false,
+ .is_dll_import = false,
  .alignment = alignment,
  .@"addrspace" = @"addrspace",
  .zir_index = sema.getOwnerCauDeclInst(), // `declaration` instruction
@@ -26958,6 +26970,7 @@ fn resolveExternOptions(
  library_name: InternPool.OptionalNullTerminatedString = .none,
  linkage: std.builtin.GlobalLinkage = .strong,
  is_thread_local: bool = false,
+ is_dll_import: bool = false,
 } {
  const pt = sema.pt;
  const zcu = pt.zcu;
@@ -26971,6 +26984,7 @@ fn resolveExternOptions(
  const library_src = block.src(.{ .init_field_library = src.offset.node_offset_builtin_call_arg.builtin_call_node });
  const linkage_src = block.src(.{ .init_field_linkage = src.offset.node_offset_builtin_call_arg.builtin_call_node });
  const thread_local_src = block.src(.{ .init_field_thread_local = src.offset.node_offset_builtin_call_arg.builtin_call_node });
+ const dll_import_src = block.src(.{ .init_field_dll_import = src.offset.node_offset_builtin_call_arg.builtin_call_node });
 
  const name_ref = try sema.fieldVal(block, src, options, try ip.getOrPutString(gpa, pt.tid, "name", .no_embedded_nulls), name_src);
  const name = try sema.toConstString(block, name_src, name_ref, .{
@@ -27004,6 +27018,11 @@ fn resolveExternOptions(
  break :library_name library_name;
  } else null;
 
+ const is_dll_import_ref = try sema.fieldVal(block, src, options, try ip.getOrPutString(gpa, pt.tid, "is_dll_import", .no_embedded_nulls), dll_import_src);
+ const is_dll_import_val = try sema.resolveConstDefinedValue(block, dll_import_src, is_dll_import_ref, .{
+ .needed_comptime_reason = "it must be comptime-known if the symbol is imported from a dll",
+ });
+
  if (name.len == 0) {
  return sema.fail(block, name_src, "extern symbol name cannot be empty", .{});
  }
@@ -27017,6 +27036,7 @@ fn resolveExternOptions(
  .library_name = try ip.getOrPutStringOpt(gpa, pt.tid, library_name, .no_embedded_nulls),
  .linkage = linkage,
  .is_thread_local = is_thread_local_val.toBool(),
+ .is_dll_import = is_dll_import_val.toBool(),
  };
 }
 
@@ -27062,6 +27082,7 @@ fn zirBuiltinExtern(
  .is_const = ptr_info.flags.is_const,
  .is_threadlocal = options.is_thread_local,
  .is_weak_linkage = options.linkage == .weak,
+ .is_dll_import = options.is_dll_import,
  .alignment = ptr_info.flags.alignment,
  .@"addrspace" = ptr_info.flags.address_space,
  // This instruction is just for source locations.

src/Value.zig

@@ -1340,11 +1340,11 @@ pub fn isLazySize(val: Value, zcu: *Zcu) bool {
  };
 }
 
-pub fn isPtrToThreadLocal(val: Value, zcu: *Zcu) bool {
+pub fn isPtrRuntimeValue(val: Value, zcu: *Zcu) bool {
  const ip = &zcu.intern_pool;
  const nav = ip.getBackingNav(val.toIntern()).unwrap() orelse return false;
  return switch (ip.indexToKey(ip.getNav(nav).status.resolved.val)) {
- .@"extern" => |e| e.is_threadlocal,
+ .@"extern" => |e| e.is_threadlocal or e.is_dll_import,
  .variable => |v| v.is_threadlocal,
  else => false,
  };

src/Zcu.zig

@@ -1522,6 +1522,7 @@ pub const SrcLoc = struct {
  .init_field_cache,
  .init_field_library,
  .init_field_thread_local,
+ .init_field_dll_import,
  => |builtin_call_node| {
  const wanted = switch (src_loc.lazy) {
  .init_field_name => "name",
@@ -1533,6 +1534,7 @@ pub const SrcLoc = struct {
  .init_field_cache => "cache",
  .init_field_library => "library",
  .init_field_thread_local => "thread_local",
+ .init_field_dll_import => "dll_import",
  else => unreachable,
  };
  const tree = try src_loc.file_scope.getTree(gpa);
@@ -1959,6 +1961,7 @@ pub const LazySrcLoc = struct {
  init_field_cache: i32,
  init_field_library: i32,
  init_field_thread_local: i32,
+ init_field_dll_import: i32,
  /// The source location points to the value of an item in a specific
  /// case of a `switch`.
  switch_case_item: SwitchItem,

src/Zcu/PerThread.zig

@@ -2763,6 +2763,7 @@ pub fn getCoerced(pt: Zcu.PerThread, val: Value, new_ty: Type) Allocator.Error!V
  .is_const = e.is_const,
  .is_threadlocal = e.is_threadlocal,
  .is_weak_linkage = e.is_weak_linkage,
+ .is_dll_import = e.is_dll_import,
  .alignment = e.alignment,
  .@"addrspace" = e.@"addrspace",
  .zir_index = e.zir_index,

src/codegen/llvm.zig

@@ -3237,10 +3237,10 @@ pub const Object = struct {
  const ip = &zcu.intern_pool;
  const nav = ip.getNav(nav_index);
  const resolved = nav.status.resolved;
- const is_extern, const is_threadlocal, const is_weak_linkage = switch (ip.indexToKey(resolved.val)) {
- .variable => |variable| .{ false, variable.is_threadlocal, variable.is_weak_linkage },
- .@"extern" => |@"extern"| .{ true, @"extern".is_threadlocal, @"extern".is_weak_linkage },
- else => .{ false, false, false },
+ const is_extern, const is_threadlocal, const is_weak_linkage, const is_dll_import = switch (ip.indexToKey(resolved.val)) {
+ .variable => |variable| .{ false, variable.is_threadlocal, variable.is_weak_linkage, false },
+ .@"extern" => |@"extern"| .{ true, @"extern".is_threadlocal, @"extern".is_weak_linkage, @"extern".is_dll_import },
+ else => .{ false, false, false, false },
  };
 
  const variable_index = try o.builder.addVariable(
@@ -3257,6 +3257,7 @@ pub const Object = struct {
  if (is_threadlocal and !zcu.navFileScope(nav_index).mod.single_threaded)
  variable_index.setThreadLocal(.generaldynamic, &o.builder);
  if (is_weak_linkage) variable_index.setLinkage(.extern_weak, &o.builder);
+ if (is_dll_import) variable_index.setDllStorageClass(.dllimport, &o.builder);
  } else {
  variable_index.setLinkage(.internal, &o.builder);
  variable_index.setUnnamedAddr(.unnamed_addr, &o.builder);
@@ -4782,10 +4783,10 @@ pub const NavGen = struct {
  const nav = ip.getNav(nav_index);
  const resolved = nav.status.resolved;
 
- const is_extern, const lib_name, const is_threadlocal, const is_weak_linkage, const is_const, const init_val, const owner_nav = switch (ip.indexToKey(resolved.val)) {
- .variable => |variable| .{ false, variable.lib_name, variable.is_threadlocal, variable.is_weak_linkage, false, variable.init, variable.owner_nav },
- .@"extern" => |@"extern"| .{ true, @"extern".lib_name, @"extern".is_threadlocal, @"extern".is_weak_linkage, @"extern".is_const, .none, @"extern".owner_nav },
- else => .{ false, .none, false, false, true, resolved.val, nav_index },
+ const is_extern, const lib_name, const is_threadlocal, const is_weak_linkage, const is_dll_import, const is_const, const init_val, const owner_nav = switch (ip.indexToKey(resolved.val)) {
+ .variable => |variable| .{ false, variable.lib_name, variable.is_threadlocal, variable.is_weak_linkage, false, false, variable.init, variable.owner_nav },
+ .@"extern" => |@"extern"| .{ true, @"extern".lib_name, @"extern".is_threadlocal, @"extern".is_weak_linkage, @"extern".is_dll_import, @"extern".is_const, .none, @"extern".owner_nav },
+ else => .{ false, .none, false, false, false, true, resolved.val, nav_index },
  };
  const ty = Type.fromInterned(nav.typeOf(ip));
 
@@ -4860,8 +4861,11 @@ pub const NavGen = struct {
  try global_index.rename(decl_name, &o.builder);
  global_index.setLinkage(.external, &o.builder);
  global_index.setUnnamedAddr(.default, &o.builder);
- if (zcu.comp.config.dll_export_fns)
+ if (is_dll_import) {
+ global_index.setDllStorageClass(.dllimport, &o.builder);
+ } else if (zcu.comp.config.dll_export_fns) {
  global_index.setDllStorageClass(.default, &o.builder);
+ }
 
  if (is_weak_linkage) global_index.setLinkage(.extern_weak, &o.builder);
  }

src/codegen/llvm/Builder.zig

@@ -2528,6 +2528,10 @@ pub const Variable = struct {
  return self.ptrConst(builder).global.setLinkage(linkage, builder);
  }
 
+ pub fn setDllStorageClass(self: Index, class: DllStorageClass, builder: *Builder) void {
+ return self.ptrConst(builder).global.setDllStorageClass(class, builder);
+ }
+
  pub fn setUnnamedAddr(self: Index, unnamed_addr: UnnamedAddr, builder: *Builder) void {
  return self.ptrConst(builder).global.setUnnamedAddr(unnamed_addr, builder);
  }

test/cases/compile_errors/builtin_extern_in_comptime_scope.zig

@@ -0,0 +1,18 @@
+const foo_tl = @extern(*i32, .{ .name = "foo", .is_thread_local = true });
+const foo_dll = @extern(*i32, .{ .name = "foo", .is_dll_import = true });
+pub export fn entry() void {
+ _ = foo_tl;
+}
+pub export fn entry2() void {
+ _ = foo_dll;
+}
+// error
+// backend=stage2
+// target=native
+//
+// :1:16: error: unable to resolve comptime value
+// :1:16: note: global variable initializer must be comptime-known
+// :1:16: note: thread local and dll imported variables have runtime-known addresses
+// :2:17: error: unable to resolve comptime value
+// :2:17: note: global variable initializer must be comptime-known
+// :2:17: note: thread local and dll imported variables have runtime-known addresses

test/standalone/extern/build.zig

@@ -1,6 +1,9 @@
 const std = @import("std");
 
 pub fn build(b: *std.Build) void {
+ const test_step = b.step("test", "Test it");
+ b.default_step = test_step;
+
  const optimize: std.builtin.OptimizeMode = .Debug;
 
  const obj = b.addObject(.{
@@ -9,12 +12,20 @@ pub fn build(b: *std.Build) void {
  .target = b.graph.host,
  .optimize = optimize,
  });
- const main = b.addTest(.{
+ const shared = b.addSharedLibrary(.{
+ .name = "shared",
+ .target = b.graph.host,
+ .optimize = optimize,
+ .link_libc = true,
+ });
+ if (b.graph.host.result.abi == .msvc) shared.defineCMacro("API", "__declspec(dllexport)");
+ shared.addCSourceFile(.{ .file = b.path("shared.c"), .flags = &.{} });
+ const test_exe = b.addTest(.{
  .root_source_file = b.path("main.zig"),
  .optimize = optimize,
  });
- main.addObject(obj);
+ test_exe.addObject(obj);
+ test_exe.linkLibrary(shared);
 
- const test_step = b.step("test", "Test it");
- test_step.dependOn(&main.step);
+ test_step.dependOn(&b.addRunArtifact(test_exe).step);
 }

test/standalone/extern/main.zig

@@ -1,4 +1,5 @@
 const assert = @import("std").debug.assert;
+const testing = @import("std").testing;
 
 const updateHidden = @extern(*const fn (u32) callconv(.C) void, .{ .name = "updateHidden" });
 const getHidden = @extern(*const fn () callconv(.C) u32, .{ .name = "getHidden" });
@@ -8,14 +9,18 @@ const T = extern struct { x: u32 };
 test {
  const mut_val_ptr = @extern(*f64, .{ .name = "mut_val" });
  const const_val_ptr = @extern(*const T, .{ .name = "const_val" });
+ const shared_val_ptr = @extern(*c_int, .{ .name = "shared_val", .is_dll_import = true });
 
  assert(getHidden() == 0);
  updateHidden(123);
  assert(getHidden() == 123);
-
  assert(mut_val_ptr.* == 1.23);
  mut_val_ptr.* = 10.0;
  assert(mut_val_ptr.* == 10.0);
 
  assert(const_val_ptr.x == 42);
+
+ assert(shared_val_ptr.* == 1234);
+ shared_val_ptr.* = 1235;
+ assert(shared_val_ptr.* == 1235);
 }

test/standalone/extern/shared.c

@@ -0,0 +1,5 @@
+#ifndef API
+#define API
+#endif
+
+API int shared_val = 1234;

lib/std/builtin.zig

@@ -683,6 +683,7 @@ pub const ExternOptions = struct {
  library_name: ?[]const u8 = null,
  linkage: GlobalLinkage = .strong,
  is_thread_local: bool = false,
+ is_dll_import: bool = false,
 };
 
 /// This data structure is used by the Zig language code generation and

src/InternPool.zig

@@ -2054,6 +2054,7 @@ pub const Key = union(enum) {
  is_const: bool,
  is_threadlocal: bool,
  is_weak_linkage: bool,
+ is_dll_import: bool,
  alignment: Alignment,
  @"addrspace": std.builtin.AddressSpace,
  /// The ZIR instruction which created this extern; used only for source locations.
@@ -2675,7 +2676,8 @@ pub const Key = union(enum) {
  asBytes(&e.ty) ++ asBytes(&e.lib_name) ++
  asBytes(&e.is_const) ++ asBytes(&e.is_threadlocal) ++
  asBytes(&e.is_weak_linkage) ++ asBytes(&e.alignment) ++
- asBytes(&e.@"addrspace") ++ asBytes(&e.zir_index)),
+ asBytes(&e.is_dll_import) ++ asBytes(&e.@"addrspace") ++
+ asBytes(&e.zir_index)),
  };
  }
 
@@ -2771,6 +2773,7 @@ pub const Key = union(enum) {
  a_info.is_const == b_info.is_const and
  a_info.is_threadlocal == b_info.is_threadlocal and
  a_info.is_weak_linkage == b_info.is_weak_linkage and
+ a_info.is_dll_import == b_info.is_dll_import and
  a_info.alignment == b_info.alignment and
  a_info.@"addrspace" == b_info.@"addrspace" and
  a_info.zir_index == b_info.zir_index;
@@ -5370,7 +5373,8 @@ pub const Tag = enum(u8) {
  is_const: bool,
  is_threadlocal: bool,
  is_weak_linkage: bool,
- _: u29 = 0,
+ is_dll_import: bool,
+ _: u28 = 0,
  };
  };
 
@@ -6715,6 +6719,7 @@ pub fn indexToKey(ip: *const InternPool, index: Index) Key {
  .is_const = extra.flags.is_const,
  .is_threadlocal = extra.flags.is_threadlocal,
  .is_weak_linkage = extra.flags.is_weak_linkage,
+ .is_dll_import = extra.flags.is_dll_import,
  .alignment = nav.status.resolved.alignment,
  .@"addrspace" = nav.status.resolved.@"addrspace",
  .zir_index = extra.zir_index,
@@ -7381,6 +7386,7 @@ pub fn get(ip: *InternPool, gpa: Allocator, tid: Zcu.PerThread.Id, key: Key) All
  .is_const = false,
  .is_threadlocal = variable.is_threadlocal,
  .is_weak_linkage = variable.is_weak_linkage,
+ .is_dll_import = false,
  },
  }),
  });
@@ -8644,6 +8650,7 @@ pub fn getExtern(
  .is_const = key.is_const,
  .is_threadlocal = key.is_threadlocal,
  .is_weak_linkage = key.is_weak_linkage,
+ .is_dll_import = key.is_dll_import,
  },
  .zir_index = key.zir_index,
  .owner_nav = owner_nav,

src/Sema.zig

@@ -876,6 +876,7 @@ const InferredAlloc = struct {
 
 const NeededComptimeReason = struct {
  needed_comptime_reason: []const u8,
+ value_comptime_reason: ?[]const u8 = null,
  block_comptime_reason: ?*const Block.ComptimeReason = null,
 };
 
@@ -2251,7 +2252,7 @@ fn resolveValueAllowVariables(sema: *Sema, inst: Air.Inst.Ref) CompileError!?Val
  }
  };
  const val = Value.fromInterned(ip_index);
- if (val.isPtrToThreadLocal(pt.zcu)) return null;
+ if (val.isPtrRuntimeValue(pt.zcu)) return null;
  return val;
 }
 
@@ -2277,8 +2278,14 @@ pub fn resolveFinalDeclValue(
  const zcu = sema.pt.zcu;
 
  const val = try sema.resolveValueAllowVariables(air_ref) orelse {
+ const value_comptime_reason: ?[]const u8 = if (air_ref.toInterned()) |_|
+ "thread local and dll imported variables have runtime-known addresses"
+ else
+ null;
+
  return sema.failWithNeededComptime(block, src, .{
  .needed_comptime_reason = "global variable initializer must be comptime-known",
+ .value_comptime_reason = value_comptime_reason,
  });
  };
  if (val.isGenericPoison()) return error.GenericPoison;
@@ -2296,6 +2303,9 @@ fn failWithNeededComptime(sema: *Sema, block: *Block, src: LazySrcLoc, reason: N
  const msg = try sema.errMsg(src, "unable to resolve comptime value", .{});
  errdefer msg.destroy(sema.gpa);
  try sema.errNote(src, msg, "{s}", .{reason.needed_comptime_reason});
+ if (reason.value_comptime_reason) |value_comptime_reason| {
+ try sema.errNote(src, msg, "{s}", .{value_comptime_reason});
+ }
 
  if (reason.block_comptime_reason) |block_comptime_reason| {
  try block_comptime_reason.explain(sema, msg);
@@ -9960,6 +9970,7 @@ fn funcCommon(
  .is_const = true,
  .is_threadlocal = false,
  .is_weak_linkage = false,
+ .is_dll_import = false,
  .alignment = alignment orelse .none,
  .@"addrspace" = address_space orelse .generic,
  .zir_index = sema.getOwnerCauDeclInst(), // `declaration` instruction
@@ -26505,6 +26516,7 @@ fn zirVarExtended(
  .is_const = small.is_const,
  .is_threadlocal = small.is_threadlocal,
  .is_weak_linkage = false,
+ .is_dll_import = false,
  .alignment = alignment,
  .@"addrspace" = @"addrspace",
  .zir_index = sema.getOwnerCauDeclInst(), // `declaration` instruction
@@ -26958,6 +26970,7 @@ fn resolveExternOptions(
  library_name: InternPool.OptionalNullTerminatedString = .none,
  linkage: std.builtin.GlobalLinkage = .strong,
  is_thread_local: bool = false,
+ is_dll_import: bool = false,
 } {
  const pt = sema.pt;
  const zcu = pt.zcu;
@@ -26971,6 +26984,7 @@ fn resolveExternOptions(
  const library_src = block.src(.{ .init_field_library = src.offset.node_offset_builtin_call_arg.builtin_call_node });
  const linkage_src = block.src(.{ .init_field_linkage = src.offset.node_offset_builtin_call_arg.builtin_call_node });
  const thread_local_src = block.src(.{ .init_field_thread_local = src.offset.node_offset_builtin_call_arg.builtin_call_node });
+ const dll_import_src = block.src(.{ .init_field_dll_import = src.offset.node_offset_builtin_call_arg.builtin_call_node });
 
  const name_ref = try sema.fieldVal(block, src, options, try ip.getOrPutString(gpa, pt.tid, "name", .no_embedded_nulls), name_src);
  const name = try sema.toConstString(block, name_src, name_ref, .{
@@ -27004,6 +27018,11 @@ fn resolveExternOptions(
  break :library_name library_name;
  } else null;
 
+ const is_dll_import_ref = try sema.fieldVal(block, src, options, try ip.getOrPutString(gpa, pt.tid, "is_dll_import", .no_embedded_nulls), dll_import_src);
+ const is_dll_import_val = try sema.resolveConstDefinedValue(block, dll_import_src, is_dll_import_ref, .{
+ .needed_comptime_reason = "it must be comptime-known if the symbol is imported from a dll",
+ });
+
  if (name.len == 0) {
  return sema.fail(block, name_src, "extern symbol name cannot be empty", .{});
  }
@@ -27017,6 +27036,7 @@ fn resolveExternOptions(
  .library_name = try ip.getOrPutStringOpt(gpa, pt.tid, library_name, .no_embedded_nulls),
  .linkage = linkage,
  .is_thread_local = is_thread_local_val.toBool(),
+ .is_dll_import = is_dll_import_val.toBool(),
  };
 }
 
@@ -27062,6 +27082,7 @@ fn zirBuiltinExtern(
  .is_const = ptr_info.flags.is_const,
  .is_threadlocal = options.is_thread_local,
  .is_weak_linkage = options.linkage == .weak,
+ .is_dll_import = options.is_dll_import,
  .alignment = ptr_info.flags.alignment,
  .@"addrspace" = ptr_info.flags.address_space,
  // This instruction is just for source locations.

src/Value.zig

@@ -1340,11 +1340,11 @@ pub fn isLazySize(val: Value, zcu: *Zcu) bool {
  };
 }
 
-pub fn isPtrToThreadLocal(val: Value, zcu: *Zcu) bool {
+pub fn isPtrRuntimeValue(val: Value, zcu: *Zcu) bool {
  const ip = &zcu.intern_pool;
  const nav = ip.getBackingNav(val.toIntern()).unwrap() orelse return false;
  return switch (ip.indexToKey(ip.getNav(nav).status.resolved.val)) {
- .@"extern" => |e| e.is_threadlocal,
+ .@"extern" => |e| e.is_threadlocal or e.is_dll_import,
  .variable => |v| v.is_threadlocal,
  else => false,
  };

src/Zcu.zig

@@ -1522,6 +1522,7 @@ pub const SrcLoc = struct {
  .init_field_cache,
  .init_field_library,
  .init_field_thread_local,
+ .init_field_dll_import,
  => |builtin_call_node| {
  const wanted = switch (src_loc.lazy) {
  .init_field_name => "name",
@@ -1533,6 +1534,7 @@ pub const SrcLoc = struct {
  .init_field_cache => "cache",
  .init_field_library => "library",
  .init_field_thread_local => "thread_local",
+ .init_field_dll_import => "dll_import",
  else => unreachable,
  };
  const tree = try src_loc.file_scope.getTree(gpa);
@@ -1959,6 +1961,7 @@ pub const LazySrcLoc = struct {
  init_field_cache: i32,
  init_field_library: i32,
  init_field_thread_local: i32,
+ init_field_dll_import: i32,
  /// The source location points to the value of an item in a specific
  /// case of a `switch`.
  switch_case_item: SwitchItem,

src/Zcu/PerThread.zig

@@ -2763,6 +2763,7 @@ pub fn getCoerced(pt: Zcu.PerThread, val: Value, new_ty: Type) Allocator.Error!V
  .is_const = e.is_const,
  .is_threadlocal = e.is_threadlocal,
  .is_weak_linkage = e.is_weak_linkage,
+ .is_dll_import = e.is_dll_import,
  .alignment = e.alignment,
  .@"addrspace" = e.@"addrspace",
  .zir_index = e.zir_index,

src/codegen/llvm.zig

@@ -3237,10 +3237,10 @@ pub const Object = struct {
  const ip = &zcu.intern_pool;
  const nav = ip.getNav(nav_index);
  const resolved = nav.status.resolved;
- const is_extern, const is_threadlocal, const is_weak_linkage = switch (ip.indexToKey(resolved.val)) {
- .variable => |variable| .{ false, variable.is_threadlocal, variable.is_weak_linkage },
- .@"extern" => |@"extern"| .{ true, @"extern".is_threadlocal, @"extern".is_weak_linkage },
- else => .{ false, false, false },
+ const is_extern, const is_threadlocal, const is_weak_linkage, const is_dll_import = switch (ip.indexToKey(resolved.val)) {
+ .variable => |variable| .{ false, variable.is_threadlocal, variable.is_weak_linkage, false },
+ .@"extern" => |@"extern"| .{ true, @"extern".is_threadlocal, @"extern".is_weak_linkage, @"extern".is_dll_import },
+ else => .{ false, false, false, false },
  };
 
  const variable_index = try o.builder.addVariable(
@@ -3257,6 +3257,7 @@ pub const Object = struct {
  if (is_threadlocal and !zcu.navFileScope(nav_index).mod.single_threaded)
  variable_index.setThreadLocal(.generaldynamic, &o.builder);
  if (is_weak_linkage) variable_index.setLinkage(.extern_weak, &o.builder);
+ if (is_dll_import) variable_index.setDllStorageClass(.dllimport, &o.builder);
  } else {
  variable_index.setLinkage(.internal, &o.builder);
  variable_index.setUnnamedAddr(.unnamed_addr, &o.builder);
@@ -4782,10 +4783,10 @@ pub const NavGen = struct {
  const nav = ip.getNav(nav_index);
  const resolved = nav.status.resolved;
 
- const is_extern, const lib_name, const is_threadlocal, const is_weak_linkage, const is_const, const init_val, const owner_nav = switch (ip.indexToKey(resolved.val)) {
- .variable => |variable| .{ false, variable.lib_name, variable.is_threadlocal, variable.is_weak_linkage, false, variable.init, variable.owner_nav },
- .@"extern" => |@"extern"| .{ true, @"extern".lib_name, @"extern".is_threadlocal, @"extern".is_weak_linkage, @"extern".is_const, .none, @"extern".owner_nav },
- else => .{ false, .none, false, false, true, resolved.val, nav_index },
+ const is_extern, const lib_name, const is_threadlocal, const is_weak_linkage, const is_dll_import, const is_const, const init_val, const owner_nav = switch (ip.indexToKey(resolved.val)) {
+ .variable => |variable| .{ false, variable.lib_name, variable.is_threadlocal, variable.is_weak_linkage, false, false, variable.init, variable.owner_nav },
+ .@"extern" => |@"extern"| .{ true, @"extern".lib_name, @"extern".is_threadlocal, @"extern".is_weak_linkage, @"extern".is_dll_import, @"extern".is_const, .none, @"extern".owner_nav },
+ else => .{ false, .none, false, false, false, true, resolved.val, nav_index },
  };
  const ty = Type.fromInterned(nav.typeOf(ip));
 
@@ -4860,8 +4861,11 @@ pub const NavGen = struct {
  try global_index.rename(decl_name, &o.builder);
  global_index.setLinkage(.external, &o.builder);
  global_index.setUnnamedAddr(.default, &o.builder);
- if (zcu.comp.config.dll_export_fns)
+ if (is_dll_import) {
+ global_index.setDllStorageClass(.dllimport, &o.builder);
+ } else if (zcu.comp.config.dll_export_fns) {
  global_index.setDllStorageClass(.default, &o.builder);
+ }
 
  if (is_weak_linkage) global_index.setLinkage(.extern_weak, &o.builder);
  }

src/codegen/llvm/Builder.zig

@@ -2528,6 +2528,10 @@ pub const Variable = struct {
  return self.ptrConst(builder).global.setLinkage(linkage, builder);
  }
 
+ pub fn setDllStorageClass(self: Index, class: DllStorageClass, builder: *Builder) void {
+ return self.ptrConst(builder).global.setDllStorageClass(class, builder);
+ }
+
  pub fn setUnnamedAddr(self: Index, unnamed_addr: UnnamedAddr, builder: *Builder) void {
  return self.ptrConst(builder).global.setUnnamedAddr(unnamed_addr, builder);
  }

test/cases/compile_errors/builtin_extern_in_comptime_scope.zig

@@ -0,0 +1,18 @@
+const foo_tl = @extern(*i32, .{ .name = "foo", .is_thread_local = true });
+const foo_dll = @extern(*i32, .{ .name = "foo", .is_dll_import = true });
+pub export fn entry() void {
+ _ = foo_tl;
+}
+pub export fn entry2() void {
+ _ = foo_dll;
+}
+// error
+// backend=stage2
+// target=native
+//
+// :1:16: error: unable to resolve comptime value
+// :1:16: note: global variable initializer must be comptime-known
+// :1:16: note: thread local and dll imported variables have runtime-known addresses
+// :2:17: error: unable to resolve comptime value
+// :2:17: note: global variable initializer must be comptime-known
+// :2:17: note: thread local and dll imported variables have runtime-known addresses

test/standalone/extern/build.zig

@@ -1,6 +1,9 @@
 const std = @import("std");
 
 pub fn build(b: *std.Build) void {
+ const test_step = b.step("test", "Test it");
+ b.default_step = test_step;
+
  const optimize: std.builtin.OptimizeMode = .Debug;
 
  const obj = b.addObject(.{
@@ -9,12 +12,20 @@ pub fn build(b: *std.Build) void {
  .target = b.graph.host,
  .optimize = optimize,
  });
- const main = b.addTest(.{
+ const shared = b.addSharedLibrary(.{
+ .name = "shared",
+ .target = b.graph.host,
+ .optimize = optimize,
+ .link_libc = true,
+ });
+ if (b.graph.host.result.abi == .msvc) shared.defineCMacro("API", "__declspec(dllexport)");
+ shared.addCSourceFile(.{ .file = b.path("shared.c"), .flags = &.{} });
+ const test_exe = b.addTest(.{
  .root_source_file = b.path("main.zig"),
  .optimize = optimize,
  });
- main.addObject(obj);
+ test_exe.addObject(obj);
+ test_exe.linkLibrary(shared);
 
- const test_step = b.step("test", "Test it");
- test_step.dependOn(&main.step);
+ test_step.dependOn(&b.addRunArtifact(test_exe).step);
 }

test/standalone/extern/main.zig

@@ -1,4 +1,5 @@
 const assert = @import("std").debug.assert;
+const testing = @import("std").testing;
 
 const updateHidden = @extern(*const fn (u32) callconv(.C) void, .{ .name = "updateHidden" });
 const getHidden = @extern(*const fn () callconv(.C) u32, .{ .name = "getHidden" });
@@ -8,14 +9,18 @@ const T = extern struct { x: u32 };
 test {
  const mut_val_ptr = @extern(*f64, .{ .name = "mut_val" });
  const const_val_ptr = @extern(*const T, .{ .name = "const_val" });
+ const shared_val_ptr = @extern(*c_int, .{ .name = "shared_val", .is_dll_import = true });
 
  assert(getHidden() == 0);
  updateHidden(123);
  assert(getHidden() == 123);
-
  assert(mut_val_ptr.* == 1.23);
  mut_val_ptr.* = 10.0;
  assert(mut_val_ptr.* == 10.0);
 
  assert(const_val_ptr.x == 42);
+
+ assert(shared_val_ptr.* == 1234);
+ shared_val_ptr.* = 1235;
+ assert(shared_val_ptr.* == 1235);
 }

test/standalone/extern/shared.c

@@ -0,0 +1,5 @@
+#ifndef API
+#define API
+#endif
+
+API int shared_val = 1234;

lib/std/builtin.zig

@@ -683,6 +683,7 @@ pub const ExternOptions = struct {
  library_name: ?[]const u8 = null,
  linkage: GlobalLinkage = .strong,
  is_thread_local: bool = false,
+ is_dll_import: bool = false,
 };
 
 /// This data structure is used by the Zig language code generation and

src/InternPool.zig

@@ -2054,6 +2054,7 @@ pub const Key = union(enum) {
  is_const: bool,
  is_threadlocal: bool,
  is_weak_linkage: bool,
+ is_dll_import: bool,
  alignment: Alignment,
  @"addrspace": std.builtin.AddressSpace,
  /// The ZIR instruction which created this extern; used only for source locations.
@@ -2675,7 +2676,8 @@ pub const Key = union(enum) {
  asBytes(&e.ty) ++ asBytes(&e.lib_name) ++
  asBytes(&e.is_const) ++ asBytes(&e.is_threadlocal) ++
  asBytes(&e.is_weak_linkage) ++ asBytes(&e.alignment) ++
- asBytes(&e.@"addrspace") ++ asBytes(&e.zir_index)),
+ asBytes(&e.is_dll_import) ++ asBytes(&e.@"addrspace") ++
+ asBytes(&e.zir_index)),
  };
  }
 
@@ -2771,6 +2773,7 @@ pub const Key = union(enum) {
  a_info.is_const == b_info.is_const and
  a_info.is_threadlocal == b_info.is_threadlocal and
  a_info.is_weak_linkage == b_info.is_weak_linkage and
+ a_info.is_dll_import == b_info.is_dll_import and
  a_info.alignment == b_info.alignment and
  a_info.@"addrspace" == b_info.@"addrspace" and
  a_info.zir_index == b_info.zir_index;
@@ -5370,7 +5373,8 @@ pub const Tag = enum(u8) {
  is_const: bool,
  is_threadlocal: bool,
  is_weak_linkage: bool,
- _: u29 = 0,
+ is_dll_import: bool,
+ _: u28 = 0,
  };
  };
 
@@ -6715,6 +6719,7 @@ pub fn indexToKey(ip: *const InternPool, index: Index) Key {
  .is_const = extra.flags.is_const,
  .is_threadlocal = extra.flags.is_threadlocal,
  .is_weak_linkage = extra.flags.is_weak_linkage,
+ .is_dll_import = extra.flags.is_dll_import,
  .alignment = nav.status.resolved.alignment,
  .@"addrspace" = nav.status.resolved.@"addrspace",
  .zir_index = extra.zir_index,
@@ -7381,6 +7386,7 @@ pub fn get(ip: *InternPool, gpa: Allocator, tid: Zcu.PerThread.Id, key: Key) All
  .is_const = false,
  .is_threadlocal = variable.is_threadlocal,
  .is_weak_linkage = variable.is_weak_linkage,
+ .is_dll_import = false,
  },
  }),
  });
@@ -8644,6 +8650,7 @@ pub fn getExtern(
  .is_const = key.is_const,
  .is_threadlocal = key.is_threadlocal,
  .is_weak_linkage = key.is_weak_linkage,
+ .is_dll_import = key.is_dll_import,
  },
  .zir_index = key.zir_index,
  .owner_nav = owner_nav,

src/Sema.zig

@@ -876,6 +876,7 @@ const InferredAlloc = struct {
 
 const NeededComptimeReason = struct {
  needed_comptime_reason: []const u8,
+ value_comptime_reason: ?[]const u8 = null,
  block_comptime_reason: ?*const Block.ComptimeReason = null,
 };
 
@@ -2251,7 +2252,7 @@ fn resolveValueAllowVariables(sema: *Sema, inst: Air.Inst.Ref) CompileError!?Val
  }
  };
  const val = Value.fromInterned(ip_index);
- if (val.isPtrToThreadLocal(pt.zcu)) return null;
+ if (val.isPtrRuntimeValue(pt.zcu)) return null;
  return val;
 }
 
@@ -2277,8 +2278,14 @@ pub fn resolveFinalDeclValue(
  const zcu = sema.pt.zcu;
 
  const val = try sema.resolveValueAllowVariables(air_ref) orelse {
+ const value_comptime_reason: ?[]const u8 = if (air_ref.toInterned()) |_|
+ "thread local and dll imported variables have runtime-known addresses"
+ else
+ null;
+
  return sema.failWithNeededComptime(block, src, .{
  .needed_comptime_reason = "global variable initializer must be comptime-known",
+ .value_comptime_reason = value_comptime_reason,
  });
  };
  if (val.isGenericPoison()) return error.GenericPoison;
@@ -2296,6 +2303,9 @@ fn failWithNeededComptime(sema: *Sema, block: *Block, src: LazySrcLoc, reason: N
  const msg = try sema.errMsg(src, "unable to resolve comptime value", .{});
  errdefer msg.destroy(sema.gpa);
  try sema.errNote(src, msg, "{s}", .{reason.needed_comptime_reason});
+ if (reason.value_comptime_reason) |value_comptime_reason| {
+ try sema.errNote(src, msg, "{s}", .{value_comptime_reason});
+ }
 
  if (reason.block_comptime_reason) |block_comptime_reason| {
  try block_comptime_reason.explain(sema, msg);
@@ -9960,6 +9970,7 @@ fn funcCommon(
  .is_const = true,
  .is_threadlocal = false,
  .is_weak_linkage = false,
+ .is_dll_import = false,
  .alignment = alignment orelse .none,
  .@"addrspace" = address_space orelse .generic,
  .zir_index = sema.getOwnerCauDeclInst(), // `declaration` instruction
@@ -26505,6 +26516,7 @@ fn zirVarExtended(
  .is_const = small.is_const,
  .is_threadlocal = small.is_threadlocal,
  .is_weak_linkage = false,
+ .is_dll_import = false,
  .alignment = alignment,
  .@"addrspace" = @"addrspace",
  .zir_index = sema.getOwnerCauDeclInst(), // `declaration` instruction
@@ -26958,6 +26970,7 @@ fn resolveExternOptions(
  library_name: InternPool.OptionalNullTerminatedString = .none,
  linkage: std.builtin.GlobalLinkage = .strong,
  is_thread_local: bool = false,
+ is_dll_import: bool = false,
 } {
  const pt = sema.pt;
  const zcu = pt.zcu;
@@ -26971,6 +26984,7 @@ fn resolveExternOptions(
  const library_src = block.src(.{ .init_field_library = src.offset.node_offset_builtin_call_arg.builtin_call_node });
  const linkage_src = block.src(.{ .init_field_linkage = src.offset.node_offset_builtin_call_arg.builtin_call_node });
  const thread_local_src = block.src(.{ .init_field_thread_local = src.offset.node_offset_builtin_call_arg.builtin_call_node });
+ const dll_import_src = block.src(.{ .init_field_dll_import = src.offset.node_offset_builtin_call_arg.builtin_call_node });
 
  const name_ref = try sema.fieldVal(block, src, options, try ip.getOrPutString(gpa, pt.tid, "name", .no_embedded_nulls), name_src);
  const name = try sema.toConstString(block, name_src, name_ref, .{
@@ -27004,6 +27018,11 @@ fn resolveExternOptions(
  break :library_name library_name;
  } else null;
 
+ const is_dll_import_ref = try sema.fieldVal(block, src, options, try ip.getOrPutString(gpa, pt.tid, "is_dll_import", .no_embedded_nulls), dll_import_src);
+ const is_dll_import_val = try sema.resolveConstDefinedValue(block, dll_import_src, is_dll_import_ref, .{
+ .needed_comptime_reason = "it must be comptime-known if the symbol is imported from a dll",
+ });
+
  if (name.len == 0) {
  return sema.fail(block, name_src, "extern symbol name cannot be empty", .{});
  }
@@ -27017,6 +27036,7 @@ fn resolveExternOptions(
  .library_name = try ip.getOrPutStringOpt(gpa, pt.tid, library_name, .no_embedded_nulls),
  .linkage = linkage,
  .is_thread_local = is_thread_local_val.toBool(),
+ .is_dll_import = is_dll_import_val.toBool(),
  };
 }
 
@@ -27062,6 +27082,7 @@ fn zirBuiltinExtern(
  .is_const = ptr_info.flags.is_const,
  .is_threadlocal = options.is_thread_local,
  .is_weak_linkage = options.linkage == .weak,
+ .is_dll_import = options.is_dll_import,
  .alignment = ptr_info.flags.alignment,
  .@"addrspace" = ptr_info.flags.address_space,
  // This instruction is just for source locations.

src/Value.zig

@@ -1340,11 +1340,11 @@ pub fn isLazySize(val: Value, zcu: *Zcu) bool {
  };
 }
 
-pub fn isPtrToThreadLocal(val: Value, zcu: *Zcu) bool {
+pub fn isPtrRuntimeValue(val: Value, zcu: *Zcu) bool {
  const ip = &zcu.intern_pool;
  const nav = ip.getBackingNav(val.toIntern()).unwrap() orelse return false;
  return switch (ip.indexToKey(ip.getNav(nav).status.resolved.val)) {
- .@"extern" => |e| e.is_threadlocal,
+ .@"extern" => |e| e.is_threadlocal or e.is_dll_import,
  .variable => |v| v.is_threadlocal,
  else => false,
  };

src/Zcu.zig

@@ -1522,6 +1522,7 @@ pub const SrcLoc = struct {
  .init_field_cache,
  .init_field_library,
  .init_field_thread_local,
+ .init_field_dll_import,
  => |builtin_call_node| {
  const wanted = switch (src_loc.lazy) {
  .init_field_name => "name",
@@ -1533,6 +1534,7 @@ pub const SrcLoc = struct {
  .init_field_cache => "cache",
  .init_field_library => "library",
  .init_field_thread_local => "thread_local",
+ .init_field_dll_import => "dll_import",
  else => unreachable,
  };
  const tree = try src_loc.file_scope.getTree(gpa);
@@ -1959,6 +1961,7 @@ pub const LazySrcLoc = struct {
  init_field_cache: i32,
  init_field_library: i32,
  init_field_thread_local: i32,
+ init_field_dll_import: i32,
  /// The source location points to the value of an item in a specific
  /// case of a `switch`.
  switch_case_item: SwitchItem,

src/Zcu/PerThread.zig

@@ -2763,6 +2763,7 @@ pub fn getCoerced(pt: Zcu.PerThread, val: Value, new_ty: Type) Allocator.Error!V
  .is_const = e.is_const,
  .is_threadlocal = e.is_threadlocal,
  .is_weak_linkage = e.is_weak_linkage,
+ .is_dll_import = e.is_dll_import,
  .alignment = e.alignment,
  .@"addrspace" = e.@"addrspace",
  .zir_index = e.zir_index,

src/codegen/llvm.zig

@@ -3237,10 +3237,10 @@ pub const Object = struct {
  const ip = &zcu.intern_pool;
  const nav = ip.getNav(nav_index);
  const resolved = nav.status.resolved;
- const is_extern, const is_threadlocal, const is_weak_linkage = switch (ip.indexToKey(resolved.val)) {
- .variable => |variable| .{ false, variable.is_threadlocal, variable.is_weak_linkage },
- .@"extern" => |@"extern"| .{ true, @"extern".is_threadlocal, @"extern".is_weak_linkage },
- else => .{ false, false, false },
+ const is_extern, const is_threadlocal, const is_weak_linkage, const is_dll_import = switch (ip.indexToKey(resolved.val)) {
+ .variable => |variable| .{ false, variable.is_threadlocal, variable.is_weak_linkage, false },
+ .@"extern" => |@"extern"| .{ true, @"extern".is_threadlocal, @"extern".is_weak_linkage, @"extern".is_dll_import },
+ else => .{ false, false, false, false },
  };
 
  const variable_index = try o.builder.addVariable(
@@ -3257,6 +3257,7 @@ pub const Object = struct {
  if (is_threadlocal and !zcu.navFileScope(nav_index).mod.single_threaded)
  variable_index.setThreadLocal(.generaldynamic, &o.builder);
  if (is_weak_linkage) variable_index.setLinkage(.extern_weak, &o.builder);
+ if (is_dll_import) variable_index.setDllStorageClass(.dllimport, &o.builder);
  } else {
  variable_index.setLinkage(.internal, &o.builder);
  variable_index.setUnnamedAddr(.unnamed_addr, &o.builder);
@@ -4782,10 +4783,10 @@ pub const NavGen = struct {
  const nav = ip.getNav(nav_index);
  const resolved = nav.status.resolved;
 
- const is_extern, const lib_name, const is_threadlocal, const is_weak_linkage, const is_const, const init_val, const owner_nav = switch (ip.indexToKey(resolved.val)) {
- .variable => |variable| .{ false, variable.lib_name, variable.is_threadlocal, variable.is_weak_linkage, false, variable.init, variable.owner_nav },
- .@"extern" => |@"extern"| .{ true, @"extern".lib_name, @"extern".is_threadlocal, @"extern".is_weak_linkage, @"extern".is_const, .none, @"extern".owner_nav },
- else => .{ false, .none, false, false, true, resolved.val, nav_index },
+ const is_extern, const lib_name, const is_threadlocal, const is_weak_linkage, const is_dll_import, const is_const, const init_val, const owner_nav = switch (ip.indexToKey(resolved.val)) {
+ .variable => |variable| .{ false, variable.lib_name, variable.is_threadlocal, variable.is_weak_linkage, false, false, variable.init, variable.owner_nav },
+ .@"extern" => |@"extern"| .{ true, @"extern".lib_name, @"extern".is_threadlocal, @"extern".is_weak_linkage, @"extern".is_dll_import, @"extern".is_const, .none, @"extern".owner_nav },
+ else => .{ false, .none, false, false, false, true, resolved.val, nav_index },
  };
  const ty = Type.fromInterned(nav.typeOf(ip));
 
@@ -4860,8 +4861,11 @@ pub const NavGen = struct {
  try global_index.rename(decl_name, &o.builder);
  global_index.setLinkage(.external, &o.builder);
  global_index.setUnnamedAddr(.default, &o.builder);
- if (zcu.comp.config.dll_export_fns)
+ if (is_dll_import) {
+ global_index.setDllStorageClass(.dllimport, &o.builder);
+ } else if (zcu.comp.config.dll_export_fns) {
  global_index.setDllStorageClass(.default, &o.builder);
+ }
 
  if (is_weak_linkage) global_index.setLinkage(.extern_weak, &o.builder);
  }

src/codegen/llvm/Builder.zig

@@ -2528,6 +2528,10 @@ pub const Variable = struct {
  return self.ptrConst(builder).global.setLinkage(linkage, builder);
  }
 
+ pub fn setDllStorageClass(self: Index, class: DllStorageClass, builder: *Builder) void {
+ return self.ptrConst(builder).global.setDllStorageClass(class, builder);
+ }
+
  pub fn setUnnamedAddr(self: Index, unnamed_addr: UnnamedAddr, builder: *Builder) void {
  return self.ptrConst(builder).global.setUnnamedAddr(unnamed_addr, builder);
  }

test/cases/compile_errors/builtin_extern_in_comptime_scope.zig

@@ -0,0 +1,18 @@
+const foo_tl = @extern(*i32, .{ .name = "foo", .is_thread_local = true });
+const foo_dll = @extern(*i32, .{ .name = "foo", .is_dll_import = true });
+pub export fn entry() void {
+ _ = foo_tl;
+}
+pub export fn entry2() void {
+ _ = foo_dll;
+}
+// error
+// backend=stage2
+// target=native
+//
+// :1:16: error: unable to resolve comptime value
+// :1:16: note: global variable initializer must be comptime-known
+// :1:16: note: thread local and dll imported variables have runtime-known addresses
+// :2:17: error: unable to resolve comptime value
+// :2:17: note: global variable initializer must be comptime-known
+// :2:17: note: thread local and dll imported variables have runtime-known addresses

test/standalone/extern/build.zig

@@ -1,6 +1,9 @@
 const std = @import("std");
 
 pub fn build(b: *std.Build) void {
+ const test_step = b.step("test", "Test it");
+ b.default_step = test_step;
+
  const optimize: std.builtin.OptimizeMode = .Debug;
 
  const obj = b.addObject(.{
@@ -9,12 +12,20 @@ pub fn build(b: *std.Build) void {
  .target = b.graph.host,
  .optimize = optimize,
  });
- const main = b.addTest(.{
+ const shared = b.addSharedLibrary(.{
+ .name = "shared",
+ .target = b.graph.host,
+ .optimize = optimize,
+ .link_libc = true,
+ });
+ if (b.graph.host.result.abi == .msvc) shared.defineCMacro("API", "__declspec(dllexport)");
+ shared.addCSourceFile(.{ .file = b.path("shared.c"), .flags = &.{} });
+ const test_exe = b.addTest(.{
  .root_source_file = b.path("main.zig"),
  .optimize = optimize,
  });
- main.addObject(obj);
+ test_exe.addObject(obj);
+ test_exe.linkLibrary(shared);
 
- const test_step = b.step("test", "Test it");
- test_step.dependOn(&main.step);
+ test_step.dependOn(&b.addRunArtifact(test_exe).step);
 }

test/standalone/extern/main.zig

@@ -1,4 +1,5 @@
 const assert = @import("std").debug.assert;
+const testing = @import("std").testing;
 
 const updateHidden = @extern(*const fn (u32) callconv(.C) void, .{ .name = "updateHidden" });
 const getHidden = @extern(*const fn () callconv(.C) u32, .{ .name = "getHidden" });
@@ -8,14 +9,18 @@ const T = extern struct { x: u32 };
 test {
  const mut_val_ptr = @extern(*f64, .{ .name = "mut_val" });
  const const_val_ptr = @extern(*const T, .{ .name = "const_val" });
+ const shared_val_ptr = @extern(*c_int, .{ .name = "shared_val", .is_dll_import = true });
 
  assert(getHidden() == 0);
  updateHidden(123);
  assert(getHidden() == 123);
-
  assert(mut_val_ptr.* == 1.23);
  mut_val_ptr.* = 10.0;
  assert(mut_val_ptr.* == 10.0);
 
  assert(const_val_ptr.x == 42);
+
+ assert(shared_val_ptr.* == 1234);
+ shared_val_ptr.* = 1235;
+ assert(shared_val_ptr.* == 1235);
 }

test/standalone/extern/shared.c

@@ -0,0 +1,5 @@
+#ifndef API
+#define API
+#endif
+
+API int shared_val = 1234;

lib/std/builtin.zig

@@ -683,6 +683,7 @@ pub const ExternOptions = struct {
  library_name: ?[]const u8 = null,
  linkage: GlobalLinkage = .strong,
  is_thread_local: bool = false,
+ is_dll_import: bool = false,
 };
 
 /// This data structure is used by the Zig language code generation and

src/InternPool.zig

@@ -2054,6 +2054,7 @@ pub const Key = union(enum) {
  is_const: bool,
  is_threadlocal: bool,
  is_weak_linkage: bool,
+ is_dll_import: bool,
  alignment: Alignment,
  @"addrspace": std.builtin.AddressSpace,
  /// The ZIR instruction which created this extern; used only for source locations.
@@ -2675,7 +2676,8 @@ pub const Key = union(enum) {
  asBytes(&e.ty) ++ asBytes(&e.lib_name) ++
  asBytes(&e.is_const) ++ asBytes(&e.is_threadlocal) ++
  asBytes(&e.is_weak_linkage) ++ asBytes(&e.alignment) ++
- asBytes(&e.@"addrspace") ++ asBytes(&e.zir_index)),
+ asBytes(&e.is_dll_import) ++ asBytes(&e.@"addrspace") ++
+ asBytes(&e.zir_index)),
  };
  }
 
@@ -2771,6 +2773,7 @@ pub const Key = union(enum) {
  a_info.is_const == b_info.is_const and
  a_info.is_threadlocal == b_info.is_threadlocal and
  a_info.is_weak_linkage == b_info.is_weak_linkage and
+ a_info.is_dll_import == b_info.is_dll_import and
  a_info.alignment == b_info.alignment and
  a_info.@"addrspace" == b_info.@"addrspace" and
  a_info.zir_index == b_info.zir_index;
@@ -5370,7 +5373,8 @@ pub const Tag = enum(u8) {
  is_const: bool,
  is_threadlocal: bool,
  is_weak_linkage: bool,
- _: u29 = 0,
+ is_dll_import: bool,
+ _: u28 = 0,
  };
  };
 
@@ -6715,6 +6719,7 @@ pub fn indexToKey(ip: *const InternPool, index: Index) Key {
  .is_const = extra.flags.is_const,
  .is_threadlocal = extra.flags.is_threadlocal,
  .is_weak_linkage = extra.flags.is_weak_linkage,
+ .is_dll_import = extra.flags.is_dll_import,
  .alignment = nav.status.resolved.alignment,
  .@"addrspace" = nav.status.resolved.@"addrspace",
  .zir_index = extra.zir_index,
@@ -7381,6 +7386,7 @@ pub fn get(ip: *InternPool, gpa: Allocator, tid: Zcu.PerThread.Id, key: Key) All
  .is_const = false,
  .is_threadlocal = variable.is_threadlocal,
  .is_weak_linkage = variable.is_weak_linkage,
+ .is_dll_import = false,
  },
  }),
  });
@@ -8644,6 +8650,7 @@ pub fn getExtern(
  .is_const = key.is_const,
  .is_threadlocal = key.is_threadlocal,
  .is_weak_linkage = key.is_weak_linkage,
+ .is_dll_import = key.is_dll_import,
  },
  .zir_index = key.zir_index,
  .owner_nav = owner_nav,

src/Sema.zig

@@ -876,6 +876,7 @@ const InferredAlloc = struct {
 
 const NeededComptimeReason = struct {
  needed_comptime_reason: []const u8,
+ value_comptime_reason: ?[]const u8 = null,
  block_comptime_reason: ?*const Block.ComptimeReason = null,
 };
 
@@ -2251,7 +2252,7 @@ fn resolveValueAllowVariables(sema: *Sema, inst: Air.Inst.Ref) CompileError!?Val
  }
  };
  const val = Value.fromInterned(ip_index);
- if (val.isPtrToThreadLocal(pt.zcu)) return null;
+ if (val.isPtrRuntimeValue(pt.zcu)) return null;
  return val;
 }
 
@@ -2277,8 +2278,14 @@ pub fn resolveFinalDeclValue(
  const zcu = sema.pt.zcu;
 
  const val = try sema.resolveValueAllowVariables(air_ref) orelse {
+ const value_comptime_reason: ?[]const u8 = if (air_ref.toInterned()) |_|
+ "thread local and dll imported variables have runtime-known addresses"
+ else
+ null;
+
  return sema.failWithNeededComptime(block, src, .{
  .needed_comptime_reason = "global variable initializer must be comptime-known",
+ .value_comptime_reason = value_comptime_reason,
  });
  };
  if (val.isGenericPoison()) return error.GenericPoison;
@@ -2296,6 +2303,9 @@ fn failWithNeededComptime(sema: *Sema, block: *Block, src: LazySrcLoc, reason: N
  const msg = try sema.errMsg(src, "unable to resolve comptime value", .{});
  errdefer msg.destroy(sema.gpa);
  try sema.errNote(src, msg, "{s}", .{reason.needed_comptime_reason});
+ if (reason.value_comptime_reason) |value_comptime_reason| {
+ try sema.errNote(src, msg, "{s}", .{value_comptime_reason});
+ }
 
  if (reason.block_comptime_reason) |block_comptime_reason| {
  try block_comptime_reason.explain(sema, msg);
@@ -9960,6 +9970,7 @@ fn funcCommon(
  .is_const = true,
  .is_threadlocal = false,
  .is_weak_linkage = false,
+ .is_dll_import = false,
  .alignment = alignment orelse .none,
  .@"addrspace" = address_space orelse .generic,
  .zir_index = sema.getOwnerCauDeclInst(), // `declaration` instruction
@@ -26505,6 +26516,7 @@ fn zirVarExtended(
  .is_const = small.is_const,
  .is_threadlocal = small.is_threadlocal,
  .is_weak_linkage = false,
+ .is_dll_import = false,
  .alignment = alignment,
  .@"addrspace" = @"addrspace",
  .zir_index = sema.getOwnerCauDeclInst(), // `declaration` instruction
@@ -26958,6 +26970,7 @@ fn resolveExternOptions(
  library_name: InternPool.OptionalNullTerminatedString = .none,
  linkage: std.builtin.GlobalLinkage = .strong,
  is_thread_local: bool = false,
+ is_dll_import: bool = false,
 } {
  const pt = sema.pt;
  const zcu = pt.zcu;
@@ -26971,6 +26984,7 @@ fn resolveExternOptions(
  const library_src = block.src(.{ .init_field_library = src.offset.node_offset_builtin_call_arg.builtin_call_node });
  const linkage_src = block.src(.{ .init_field_linkage = src.offset.node_offset_builtin_call_arg.builtin_call_node });
  const thread_local_src = block.src(.{ .init_field_thread_local = src.offset.node_offset_builtin_call_arg.builtin_call_node });
+ const dll_import_src = block.src(.{ .init_field_dll_import = src.offset.node_offset_builtin_call_arg.builtin_call_node });
 
  const name_ref = try sema.fieldVal(block, src, options, try ip.getOrPutString(gpa, pt.tid, "name", .no_embedded_nulls), name_src);
  const name = try sema.toConstString(block, name_src, name_ref, .{
@@ -27004,6 +27018,11 @@ fn resolveExternOptions(
  break :library_name library_name;
  } else null;
 
+ const is_dll_import_ref = try sema.fieldVal(block, src, options, try ip.getOrPutString(gpa, pt.tid, "is_dll_import", .no_embedded_nulls), dll_import_src);
+ const is_dll_import_val = try sema.resolveConstDefinedValue(block, dll_import_src, is_dll_import_ref, .{
+ .needed_comptime_reason = "it must be comptime-known if the symbol is imported from a dll",
+ });
+
  if (name.len == 0) {
  return sema.fail(block, name_src, "extern symbol name cannot be empty", .{});
  }
@@ -27017,6 +27036,7 @@ fn resolveExternOptions(
  .library_name = try ip.getOrPutStringOpt(gpa, pt.tid, library_name, .no_embedded_nulls),
  .linkage = linkage,
  .is_thread_local = is_thread_local_val.toBool(),
+ .is_dll_import = is_dll_import_val.toBool(),
  };
 }
 
@@ -27062,6 +27082,7 @@ fn zirBuiltinExtern(
  .is_const = ptr_info.flags.is_const,
  .is_threadlocal = options.is_thread_local,
  .is_weak_linkage = options.linkage == .weak,
+ .is_dll_import = options.is_dll_import,
  .alignment = ptr_info.flags.alignment,
  .@"addrspace" = ptr_info.flags.address_space,
  // This instruction is just for source locations.

src/Value.zig

@@ -1340,11 +1340,11 @@ pub fn isLazySize(val: Value, zcu: *Zcu) bool {
  };
 }
 
-pub fn isPtrToThreadLocal(val: Value, zcu: *Zcu) bool {
+pub fn isPtrRuntimeValue(val: Value, zcu: *Zcu) bool {
  const ip = &zcu.intern_pool;
  const nav = ip.getBackingNav(val.toIntern()).unwrap() orelse return false;
  return switch (ip.indexToKey(ip.getNav(nav).status.resolved.val)) {
- .@"extern" => |e| e.is_threadlocal,
+ .@"extern" => |e| e.is_threadlocal or e.is_dll_import,
  .variable => |v| v.is_threadlocal,
  else => false,
  };

src/Zcu.zig

@@ -1522,6 +1522,7 @@ pub const SrcLoc = struct {
  .init_field_cache,
  .init_field_library,
  .init_field_thread_local,
+ .init_field_dll_import,
  => |builtin_call_node| {
  const wanted = switch (src_loc.lazy) {
  .init_field_name => "name",
@@ -1533,6 +1534,7 @@ pub const SrcLoc = struct {
  .init_field_cache => "cache",
  .init_field_library => "library",
  .init_field_thread_local => "thread_local",
+ .init_field_dll_import => "dll_import",
  else => unreachable,
  };
  const tree = try src_loc.file_scope.getTree(gpa);
@@ -1959,6 +1961,7 @@ pub const LazySrcLoc = struct {
  init_field_cache: i32,
  init_field_library: i32,
  init_field_thread_local: i32,
+ init_field_dll_import: i32,
  /// The source location points to the value of an item in a specific
  /// case of a `switch`.
  switch_case_item: SwitchItem,

src/Zcu/PerThread.zig

@@ -2763,6 +2763,7 @@ pub fn getCoerced(pt: Zcu.PerThread, val: Value, new_ty: Type) Allocator.Error!V
  .is_const = e.is_const,
  .is_threadlocal = e.is_threadlocal,
  .is_weak_linkage = e.is_weak_linkage,
+ .is_dll_import = e.is_dll_import,
  .alignment = e.alignment,
  .@"addrspace" = e.@"addrspace",
  .zir_index = e.zir_index,

src/codegen/llvm.zig

@@ -3237,10 +3237,10 @@ pub const Object = struct {
  const ip = &zcu.intern_pool;
  const nav = ip.getNav(nav_index);
  const resolved = nav.status.resolved;
- const is_extern, const is_threadlocal, const is_weak_linkage = switch (ip.indexToKey(resolved.val)) {
- .variable => |variable| .{ false, variable.is_threadlocal, variable.is_weak_linkage },
- .@"extern" => |@"extern"| .{ true, @"extern".is_threadlocal, @"extern".is_weak_linkage },
- else => .{ false, false, false },
+ const is_extern, const is_threadlocal, const is_weak_linkage, const is_dll_import = switch (ip.indexToKey(resolved.val)) {
+ .variable => |variable| .{ false, variable.is_threadlocal, variable.is_weak_linkage, false },
+ .@"extern" => |@"extern"| .{ true, @"extern".is_threadlocal, @"extern".is_weak_linkage, @"extern".is_dll_import },
+ else => .{ false, false, false, false },
  };
 
  const variable_index = try o.builder.addVariable(
@@ -3257,6 +3257,7 @@ pub const Object = struct {
  if (is_threadlocal and !zcu.navFileScope(nav_index).mod.single_threaded)
  variable_index.setThreadLocal(.generaldynamic, &o.builder);
  if (is_weak_linkage) variable_index.setLinkage(.extern_weak, &o.builder);
+ if (is_dll_import) variable_index.setDllStorageClass(.dllimport, &o.builder);
  } else {
  variable_index.setLinkage(.internal, &o.builder);
  variable_index.setUnnamedAddr(.unnamed_addr, &o.builder);
@@ -4782,10 +4783,10 @@ pub const NavGen = struct {
  const nav = ip.getNav(nav_index);
  const resolved = nav.status.resolved;
 
- const is_extern, const lib_name, const is_threadlocal, const is_weak_linkage, const is_const, const init_val, const owner_nav = switch (ip.indexToKey(resolved.val)) {
- .variable => |variable| .{ false, variable.lib_name, variable.is_threadlocal, variable.is_weak_linkage, false, variable.init, variable.owner_nav },
- .@"extern" => |@"extern"| .{ true, @"extern".lib_name, @"extern".is_threadlocal, @"extern".is_weak_linkage, @"extern".is_const, .none, @"extern".owner_nav },
- else => .{ false, .none, false, false, true, resolved.val, nav_index },
+ const is_extern, const lib_name, const is_threadlocal, const is_weak_linkage, const is_dll_import, const is_const, const init_val, const owner_nav = switch (ip.indexToKey(resolved.val)) {
+ .variable => |variable| .{ false, variable.lib_name, variable.is_threadlocal, variable.is_weak_linkage, false, false, variable.init, variable.owner_nav },
+ .@"extern" => |@"extern"| .{ true, @"extern".lib_name, @"extern".is_threadlocal, @"extern".is_weak_linkage, @"extern".is_dll_import, @"extern".is_const, .none, @"extern".owner_nav },
+ else => .{ false, .none, false, false, false, true, resolved.val, nav_index },
  };
  const ty = Type.fromInterned(nav.typeOf(ip));
 
@@ -4860,8 +4861,11 @@ pub const NavGen = struct {
  try global_index.rename(decl_name, &o.builder);
  global_index.setLinkage(.external, &o.builder);
  global_index.setUnnamedAddr(.default, &o.builder);
- if (zcu.comp.config.dll_export_fns)
+ if (is_dll_import) {
+ global_index.setDllStorageClass(.dllimport, &o.builder);
+ } else if (zcu.comp.config.dll_export_fns) {
  global_index.setDllStorageClass(.default, &o.builder);
+ }
 
  if (is_weak_linkage) global_index.setLinkage(.extern_weak, &o.builder);
  }

src/codegen/llvm/Builder.zig

@@ -2528,6 +2528,10 @@ pub const Variable = struct {
  return self.ptrConst(builder).global.setLinkage(linkage, builder);
  }
 
+ pub fn setDllStorageClass(self: Index, class: DllStorageClass, builder: *Builder) void {
+ return self.ptrConst(builder).global.setDllStorageClass(class, builder);
+ }
+
  pub fn setUnnamedAddr(self: Index, unnamed_addr: UnnamedAddr, builder: *Builder) void {
  return self.ptrConst(builder).global.setUnnamedAddr(unnamed_addr, builder);
  }

test/cases/compile_errors/builtin_extern_in_comptime_scope.zig

@@ -0,0 +1,18 @@
+const foo_tl = @extern(*i32, .{ .name = "foo", .is_thread_local = true });
+const foo_dll = @extern(*i32, .{ .name = "foo", .is_dll_import = true });
+pub export fn entry() void {
+ _ = foo_tl;
+}
+pub export fn entry2() void {
+ _ = foo_dll;
+}
+// error
+// backend=stage2
+// target=native
+//
+// :1:16: error: unable to resolve comptime value
+// :1:16: note: global variable initializer must be comptime-known
+// :1:16: note: thread local and dll imported variables have runtime-known addresses
+// :2:17: error: unable to resolve comptime value
+// :2:17: note: global variable initializer must be comptime-known
+// :2:17: note: thread local and dll imported variables have runtime-known addresses

test/standalone/extern/build.zig

@@ -1,6 +1,9 @@
 const std = @import("std");
 
 pub fn build(b: *std.Build) void {
+ const test_step = b.step("test", "Test it");
+ b.default_step = test_step;
+
  const optimize: std.builtin.OptimizeMode = .Debug;
 
  const obj = b.addObject(.{
@@ -9,12 +12,20 @@ pub fn build(b: *std.Build) void {
  .target = b.graph.host,
  .optimize = optimize,
  });
- const main = b.addTest(.{
+ const shared = b.addSharedLibrary(.{
+ .name = "shared",
+ .target = b.graph.host,
+ .optimize = optimize,
+ .link_libc = true,
+ });
+ if (b.graph.host.result.abi == .msvc) shared.defineCMacro("API", "__declspec(dllexport)");
+ shared.addCSourceFile(.{ .file = b.path("shared.c"), .flags = &.{} });
+ const test_exe = b.addTest(.{
  .root_source_file = b.path("main.zig"),
  .optimize = optimize,
  });
- main.addObject(obj);
+ test_exe.addObject(obj);
+ test_exe.linkLibrary(shared);
 
- const test_step = b.step("test", "Test it");
- test_step.dependOn(&main.step);
+ test_step.dependOn(&b.addRunArtifact(test_exe).step);
 }

test/standalone/extern/main.zig

@@ -1,4 +1,5 @@
 const assert = @import("std").debug.assert;
+const testing = @import("std").testing;
 
 const updateHidden = @extern(*const fn (u32) callconv(.C) void, .{ .name = "updateHidden" });
 const getHidden = @extern(*const fn () callconv(.C) u32, .{ .name = "getHidden" });
@@ -8,14 +9,18 @@ const T = extern struct { x: u32 };
 test {
  const mut_val_ptr = @extern(*f64, .{ .name = "mut_val" });
  const const_val_ptr = @extern(*const T, .{ .name = "const_val" });
+ const shared_val_ptr = @extern(*c_int, .{ .name = "shared_val", .is_dll_import = true });
 
  assert(getHidden() == 0);
  updateHidden(123);
  assert(getHidden() == 123);
-
  assert(mut_val_ptr.* == 1.23);
  mut_val_ptr.* = 10.0;
  assert(mut_val_ptr.* == 10.0);
 
  assert(const_val_ptr.x == 42);
+
+ assert(shared_val_ptr.* == 1234);
+ shared_val_ptr.* = 1235;
+ assert(shared_val_ptr.* == 1235);
 }

test/standalone/extern/shared.c

@@ -0,0 +1,5 @@
+#ifndef API
+#define API
+#endif
+
+API int shared_val = 1234;