can't get errno when libc lstat returns -1

[tw4452852]

Zig Version

0.9.1

Steps to Reproduce

const std = @import("std");
const c = @cImport({
    @cInclude("sys/stat.h");
});

pub fn main() anyerror!void {
    var stbuf: c.struct_stat = undefined;
    const ret = c.lstat("/no/exist/path", &stbuf);
    std.debug.print("ret = {}, c.errno = {}\n", .{ ret, std.c._errno().* });
}

Expected Behavior

The output should be: ret = -1, c.errno = 2.

Actual Behavior

But the actual output is ret = -1, c.errno = 0. The errno is not set correctly.

[Biolunar]

I’ve just stumbled upon this bug aswell when I was using Zig to compile C++ code on Linux. It works correctly with musl as the target, but is broken with glibc. I’m on Zig version 0.10.0-dev.2674+d980c6a38

[tw4452852]

I did some investigations on this issue and I think I found the culprit: zig has its own implementation of lstat here, so it has its own errno, but std.c._errno() gets external libc's errno which is different from it.

So this explains why we didn't get the correct errno when lstat.

[konstin]

This breaks using libgit2 with zig cc for me, since it relies on the lstat errno when creating the directory for cloning a repository (https://github.com/libgit2/libgit2/blob/1327dbcf2a4273a8ba6fd978db5f0882530af94d/src/util/futils.c#L527-L535)

[vrischmann]

This breaks using libgit2 with zig cc for me, since it relies on the lstat errno when creating the directory for cloning a repository (https://github.com/libgit2/libgit2/blob/1327dbcf2a4273a8ba6fd978db5f0882530af94d/src/util/futils.c#L527-L535)

Pretty sure I'm experiencing the same problem with sqlite which uses ltstat/errno to validate the path of a database to open.