std.zig.system: use both PATH and hardcoded locations to find env (2 version)

[BratishkaErik]

This is second attempt after #21540 was reverted before. In this version relative paths are handled too.

Diff compare:

diff --git a/lib/std/zig/system.zig b/lib/std/zig/system.zig
index 2376334c5c..e00d2e5dfe 100644
--- a/lib/std/zig/system.zig+++ b/lib/std/zig/system.zig@@ -1004,8 +1004,15 @@ fn glibcVerFromSoFile(file: fs.File) !std.SemanticVersion {
///
/// If it finds ELF magic sequence, file is considered an ELF file and function returns.
fn resolveElfFileRecursively(cwd: fs.Dir, start_path: []const u8) error{UnableToFindElfFile}!fs.File {
- var current_path = start_path;+ var current_path: std.BoundedArray(u8, fs.max_path_bytes) = .{};+ current_path.appendSliceAssumeCapacity(start_path);+ // Needed for storing `fs.path.resolve` result.+ var buf: [fs.max_path_bytes + 1]u8 = undefined;+ var fbs: std.heap.FixedBufferAllocator = .init(&buf);+ const allocator = fbs.allocator();++ // Needed for storing file content.
// According to `man 2 execve`:
//
// The kernel imposes a maximum length on the text
@@ -1018,11 +1025,8 @@ fn resolveElfFileRecursively(cwd: fs.Dir, start_path: []const u8) error{UnableTo
// *including* "#!" characters and ignoring newline.
// For safety, we set max length as 255 + \n (1).
var buffer: [255 + 1]u8 = undefined;
- while (true) {- // Interpreter path can be relative on Linux, but- // for simplicity we are asserting it is an absolute path.- assert(std.fs.path.isAbsolute(current_path));- const file = cwd.openFile(current_path, .{}) catch |err| switch (err) {+ while (true) : (fbs.reset()) {+ const file = cwd.openFile(current_path.constSlice(), .{}) catch |err| switch (err) {
error.NoSpaceLeft => unreachable,
error.NameTooLong => unreachable,
error.PathAlreadyExists => unreachable,
@@ -1056,37 +1060,67 @@ fn resolveElfFileRecursively(cwd: fs.Dir, start_path: []const u8) error{UnableTo
var is_elf_file = false;
defer if (is_elf_file == false) file.close();
- // Shortest working interpreter path is "#!/i" (4)- // (interpreter is "/i", assuming all paths are absolute, like in above comment).- // ELF magic number length is also 4.- //- // If file is shorter than that, it is definitely not ELF file- // nor file with "shebang" line.- const min_len = 4;-- const len = preadAtLeast(file, &buffer, 0, min_len) catch return error.UnableToFindElfFile;+ // Shortest working interpreter path is "#!i" (3)+ // (interpreter is "i", relative to file itself).+ // ELF magic number length is 4.+ const len = preadAtLeast(file, &buffer, 0, 4) catch |err| switch (err) {+ error.UnexpectedEndOfFile => preadAtLeast(file, &buffer, 0, 3) catch+ // If file is shorter than that, it is definitely not ELF file+ // nor file with "shebang" line.+ return error.UnableToFindElfFile,+ else => return error.UnableToFindElfFile,+ };
const content = buffer[0..len];
- if (mem.eql(u8, content[0..4], std.elf.MAGIC)) {+ if (len > 4 and mem.eql(u8, content[0..4], std.elf.MAGIC)) {
// It is very likely ELF file!
is_elf_file = true;
return file;
} else if (mem.eql(u8, content[0..2], "#!")) {
// We detected shebang, now parse entire line.
+ const interpreter_path = interpreter_path: {+ // Trim leading "#!" and separate line from others.+ const first_line = content[2 .. mem.indexOfScalar(u8, content, '\n') orelse content.len];- // Trim leading "#!", spaces and tabs.- const trimmed_line = mem.trimLeft(u8, content[2..], &.{ ' ', '\t' });+ // Trim leading spaces and tabs.+ const trimmed_line = mem.trimLeft(u8, first_line, &.{ ' ', '\t' });- // This line can have:- // * Interpreter path only,- // * Interpreter path and arguments, all separated by space, tab or NUL character.- // And optionally newline at the end.- const path_maybe_args = mem.trimRight(u8, trimmed_line, "\n");+ // This line can have:+ // * Interpreter path only,+ // * Interpreter path and arguments, all separated by space, tab or NUL character.+ // And optionally newline at the end.+ const path_maybe_args = mem.trimRight(u8, trimmed_line, "\n");- // Separate path and args.- const path_end = mem.indexOfAny(u8, path_maybe_args, &.{ ' ', '\t', 0 }) orelse path_maybe_args.len;+ // Separate path and args.+ const path_end = mem.indexOfAny(u8, path_maybe_args, &.{ ' ', '\t', 0 }) orelse path_maybe_args.len;- current_path = path_maybe_args[0..path_end];+ break :interpreter_path path_maybe_args[0..path_end];+ };++ // We want these scenarios to work without using `realpath`:+ // * Interpreter is absolute/relative path and real file.+ // * Interpreter is absolute/relative path and absolute/relative symlink.+ const interpreter_real_path = interpreter_real_path: {+ var readlink_buffer: [std.fs.max_path_bytes]u8 = undefined;++ const interpreter_real_path = cwd.readLink(interpreter_path, &readlink_buffer) catch |err| switch (err) {+ error.NotLink => interpreter_path,+ else => return error.UnableToFindElfFile,+ };++ const next_path = fs.path.resolve(allocator, &.{+ // `dirname` can return `null` in two situations:+ // * When path is '/': impossible since it always contain file path.+ // * When path is "some_current_dir_file": use ".".+ fs.path.dirname(interpreter_path) orelse ".",+ interpreter_real_path,+ }) catch return error.UnableToFindElfFile;++ break :interpreter_real_path next_path;+ };++ current_path.clear();+ current_path.appendSliceAssumeCapacity(interpreter_real_path);
continue;
} else {
// Not a ELF file, not a shell script with "shebang line", invalid duck.
@@ -1178,7 +1212,7 @@ fn detectAbiAndDynamicLinker(
const ld_info_list = ld_info_list_buffer[0..ld_info_list_len];
- const cwd = std.fs.cwd();+ const cwd = fs.cwd();
// Algorithm is:
// 1a) try_path: If PATH is non-empty and `env` file was found in one of the directories, use that.
@@ -1190,12 +1224,12 @@ fn detectAbiAndDynamicLinker(
const PATH = std.posix.getenv("PATH") orelse break :try_path null;
var it = mem.tokenizeScalar(u8, PATH, fs.path.delimiter);
- var buf: [std.fs.max_path_bytes + 1]u8 = undefined;+ var buf: [fs.max_path_bytes + 1]u8 = undefined;
var fbs: std.heap.FixedBufferAllocator = .init(&buf);
const allocator = fbs.allocator();
while (it.next()) |path| : (fbs.reset()) {
- const start_path = std.fs.path.joinZ(allocator, &.{ path, "env" }) catch |err| switch (err) {+ const start_path = fs.path.join(allocator, &.{ path, "env" }) catch |err| switch (err) {
error.OutOfMemory => continue,
};

I have tested with following files:

$ PATH="./:/usr/sbin" /usr/bin/zig build --zig-lib-dir ~/github.com/zig/lib
# env#!/home/bratishkaerik/github.com/zig/a# a#!../../../../bin/env# /bin/env#!/usr/bin/coreutils --coreutils-prog-shebang=env# /usr/bin/coreutils
ELF 64-bit LSB pie executable, x86-64, version 1 (SYSV), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, for GNU/Linux 3.2.0, stripped

[BratishkaErik]

Turns out it did not worked with mix of relative interpreters and symlinks, so I rewrote it a little bit:

info: current_path = ./env
error: shebang read!
error: interpreter (real ) = a
error: interpreter (readlink) = a
error: next_path = a
info: current_path = a
error: shebang read!
error: interpreter (real ) = ../../../../bin/env
error: interpreter (readlink) = ../../../../bin/env
error: next_path = ../../../../../../../bin/env
info: current_path = ../../../../../../../bin/env
error: shebang read!
error: interpreter (real ) = /usr/bin/coreutils
error: interpreter (readlink) = /usr/bin/coreutils
error: next_path = /usr/bin/coreutils
info: current_path = /usr/bin/coreutils
error: target = ...

info: current_path = ./env
error: shebang read!
error: interpreter (real ) = symlinked/interpreter
error: interpreter (readlink) = ../interpreter_with_relative_interpreter
error: next_path = interpreter_with_relative_interpreter
info: current_path = interpreter_with_relative_interpreter
error: shebang read!
error: interpreter (real ) = cant_find_this_interpreter
error: interpreter (readlink) = cant_find_this_interpreter
error: next_path = cant_find_this_interpreter
info: current_path = cant_find_this_interpreter
error: shebang read!
error: interpreter (real ) = /usr/bin/file
error: interpreter (readlink) = /usr/bin/file
error: next_path = /usr/bin/file
info: current_path = /usr/bin/file
error: target = ...

.
├── symlinked
│ └── interpreter -> ../interpreter_with_relative_interpreter
├── cant_find_this_interpreter
├── file_with_relative_symlinked_interpreter
├── interpreter_with_relative_interpreter
└── env -> file_with_relative_symlinked_interpreter
1) env a.k.a file_with_relative_symlinked_interpreter
#!symlinked/interpreter
2) symlinked/interpreter a.k.a interpreter_with_relative_interpreter
#!cant_find_this_interpreter
3) cant_find_this_interpreter
#!/usr/bin/fileecho"Hello?"# Alternatively:.
├── symlinked
│ └── 2 -> ../real_2
├── 3
├── env
└── real_2

[alexrp]

Do you think this is important to get into 0.14.0? (Given the unexpected breakage in v1 of this PR, I'm a bit worried that it might be risky so close to the release.)

[BratishkaErik]

Do you think this is important to get into 0.14.0? (Given the unexpected breakage in v1 of this PR, I'm a bit worried that it might be risky so close to the release.)

Hmmm... out of my existing PRs I would probably put this at the lowest priority, #22552 and #19975 are more important for me than this PR - it is much easier to patch or workaround this issue than others:

• env location search is already patched/replaced in affected distros
• Without std.Build: add support for adding specific global search paths #22552 you need to patch build.zig
  to add your full temporary search path here, sometimes in dependencies too
• To fetch all dependencies without zig build: allow to choose "lazy mode" for fetching process #19975 you need to write some code which will download them manually, see PRs that mention it

[alexrp]

This'll need a rebase after #19928.

[BratishkaErik]

This'll need a rebase after #19928.

I think the conflict was from #23007, StaticElfFile touched different code block.

[alexrp]

This still looks valuable to me, but the PR has obviously gotten a bit out of sync with Zig master on Codeberg, so please resubmit there if you still want this included.