null pointer is not 0 when calling into a dynamically linked library with the self-hosted compiler

[agagniere]

Zig Version

0.16.0-dev.1442, 0.15.2

Steps to Reproduce and Observed Behavior

On linux amd64, compile:

const std = @import("std");

const c = @cImport({
 @cInclude("grpc/grpc.h");
});

pub fn main() !void {
 const s: c.grpc_slice = .{
 .refcount = null,
 .data = .{ .inlined = .{
 .length = 5,
 .bytes = "Hello\x00\x00_____-----_____\x00".*,
 } },
 };
 const d: c.gpr_timespec = .{ .tv_sec = 1, .clock_type = c.GPR_TIMESPAN };

 _ = c.grpc_channel_create_call(
 @ptrFromInt(0xDeadBeef),
 null,
 0,
 @ptrFromInt(0xCafeBabe),
 s,
 &s,
 d,
 null,
 );
}

$ zig build-exe minrep.zig -l grpc -fno-llvm # possibly -L ... -I ...
$ ldd minrep
	libgrpc.so.51 => [...]/libgrpc.so.51 (0x00007f69da200000)
[...]

Then using gdb, stop at the first line of the called function

$ gdb minrep
(gdb) break grpc_channel_create_call$plt
Breakpoint 1 at 0x101d020
(gdb) run
Breakpoint 1, 0x000000000101d020 in grpc_channel_create_call$plt ()
(gdb) step
grpc_channel_create_call (channel=0x7fffffffd7e0, parent_call=0x10870f0 <os.linux.x86_64.restore_rt>, propagation_mask=32767, completion_queue=0x7fffffffd958, method=..., host=0x20,
 deadline=..., reserved=0x7fffffffd810) at src/core/lib/surface/channel.cc:104
104 gpr_timespec deadline, void* reserved) {
(gdb) step
105 GRPC_CHECK(!reserved);
(gdb) info args
channel = 0xdeadbeef
parent_call = 0x0
propagation_mask = 0
completion_queue = 0xcafebabe
method = [...]
host = 0x11a3040 <__anon_26790>
deadline = {tv_sec = 1, tv_nsec = 0, clock_type = GPR_TIMESPAN}
reserved = 0x7fffffffdac8

we can see that reserved is not 0

(Note: I built libgrpc locally to get the debug symbols)

Expected Behavior

Using the LLVM backend results in the expected behavior:

$ zig build-exe minrep.zig -L ~/Clones/grpc/libs/dbg -l grpc -I ~/Clones/grpc/include/ -fllvm
$ gdb minrep
(gdb) break grpc_channel_create_call
Breakpoint 1 at 0x11290c0
(gdb) run
Breakpoint 1, grpc_channel_create_call (channel=0xdeadbeef, parent_call=0x0, propagation_mask=0, completion_queue=0xcafebabe, method=..., host=0x100d700 <__anon_27427>, deadline=...,
 reserved=0x0) at src/core/lib/surface/channel.cc:104
104 gpr_timespec deadline, void* reserved) {
(gdb) step
105 GRPC_CHECK(!reserved);
(gdb) info args
channel = 0xdeadbeef
parent_call = 0x0
propagation_mask = 0
completion_queue = 0xcafebabe
method = [...]
host = 0x100d700 <__anon_27427>
deadline = {tv_sec = 1, tv_nsec = 0, clock_type = GPR_TIMESPAN}
reserved = 0x0

Here reserved in 0

[andrewrk]

Fixed by https://codeberg.org/ziglang/zig/pulls/30002