Truncate user and group ids for 64 bit Linux systems

[klingtnet]

Calls to getuid, getgid and their eid variants fail to compile on
64bit Linux systems because the return value of the syscall is of
usize and needs to be truncated to fit the size of uid_t that is 32
bit.

Thanks to @FireFox317 for figuring this out in Zig's Discord channel!

TODO

• squash commits
• fix CI test
• run regression test

[FireFox317]

Thanks for the fast PR @klingtnet ! I have a couple suggestions.

[LemonBoy]

What about a nice test in os/linux/test.zig so that it won't accidentally regress?
Something like:

test "" {
    expectEqual(getauxval(AT_UID), getuid());
    // same for AT_GID, AT_EUID, AT_EGID
}

[klingtnet]

What about a nice test in os/linux/test.zig so that it won't accidentally regress?
Something like:

test "" {
    expectEqual(getauxval(AT_UID), getuid());
    // same for AT_GID, AT_EUID, AT_EGID
}

Sounds fine to me, will address this after work.

[klingtnet]

I added a regression test as suggested, unfortunately I could not find any documentation on how to run them.

If it does not exist already then there should be some documentation for new contributors.

[LemonBoy]

I added a regression test as suggested, unfortunately I could not find any documentation on how to run them.

If it does not exist already then there should be some documentation for new contributors.

You can simply run zig test <your .zig file>, that's much faster than running the whole test suite (that you can run with zig build --build-file ../build.zig test-std, YMMV).

[klingtnet]

I added a regression test as suggested, unfortunately I could not find any documentation on how to run them.
If it does not exist already then there should be some documentation for new contributors.

You can simply run zig test <your .zig file>, that's much faster than running the whole test suite (that you can run with zig build --build-file ../build.zig test-std, YMMV).

Thank you very much! Test's will probably fail with 0.7.1 so I need to wait until my fresh build is ready (required to install llvm and lld, luckily the latter one was mentioned in #419 ).

Side note:

The test does not compile with 0,7.1:

$ zig test lib/std/os/linux/test.zig
./lib/std/os/linux/test.zig:6:13: error: import of file outside package path: '../../std.zig'
const std = @import("../../std.zig");
            ^
./lib/std/os/linux/test.zig:13:12: note: referenced here
const fs = std.fs;
           ^
./lib/std/os/linux/test.zig:17:22: note: referenced here
    const file = try fs.cwd().createFile(path, .{ .truncate = true, .mode = 0o666 });

[LemonBoy]

The test does not compile with 0,7.1:

Yes, some tests are not meant to be run stand-alone. You want to run lib/std/os.zig here.

[klingtnet]

So, to run the tests locally I needed to compile zig locally under Arch Linux. I will list the important steps here for documentation purposes:

$ pacman -S llvm clang lld
# follow the wiki instructions
$ cmake .. -DZIG_PREFER_CLANG_CPP_DYLIB=True
# wait ... done

The test still does not compile:

$ build/zig test lib/std/os/linux/test.zig
./lib/std/os/linux/test.zig:105:17: error: use of undeclared identifier 'getauxval'
    expectEqual(getauxval(AT_UID), getuid());
                ^

I imported getauxval from std.os.linux and then it fails with:

$ build/zig test lib/std/os/linux/test.zig | clipit
./lib/std/os/linux/test.zig:105:17: error: use of undeclared identifier 'getauxval'
    expectEqual(getauxval(AT_UID), getuid());
                ^

Unfortunately, I could not find a reference to AT_UID to import it.

[LemonBoy]

I imported getauxval from std.os.linux and then it fails with:

You can use linux.getauxval instead of defining an extra const for something that's only used once.

I imported getauxval from std.os.linux and then it fails with:

Those are defined in std.elf... It makes no sense, I know.

[klingtnet]

Seems to work fine now:

$ build/zig test lib/std/os/linux/test.zig
All 5 tests passed.
s1 alinz@kn-portable

[klingtnet]

I need to fix the failing CI test:

1081/1637 os.linux.test.test "std-native-Debug-c-multi user and group ids"... expected 0, found 1001
/home/vsts/work/1/s/lib/std/testing.zig:74:32: 0x44178f in testing.expectEqual (test)
                std.debug.panic("expected {}, found {}", .{ expected, actual });
                               ^
/home/vsts/work/1/s/lib/std/os/linux/test.zig:105:16: 0x38807e in os.linux.test.test "std-native-Debug-c-multi user and group ids" (test)
    expectEqual(linux.getauxval(elf.AT_UID), linux.getuid());
               ^
/home/vsts/work/1/s/lib/std/special/test_runner.zig:61:28: 0x3c0a58 in std.special.main (test)
        } else test_fn.func();
                           ^
/home/vsts/work/1/s/lib/std/start.zig:344:37: 0x3c27a1 in start.main (test)
            const result = root.main() catch |err| {
                                    ^
error: the following test command crashed:
/home/vsts/work/1/s/zig-cache/o/590cc85149a19cdf50140d5408f6d1bb/test
The following command exited with error code 1:
/home/vsts/work/1/s/build/zig test /home/vsts/work/1/s/lib/std/std.zig -lc --test-name-prefix std-native-Debug-c-multi  --cache-dir /home/vsts/work/1/s/zig-cache --global-cache-dir /home/vsts/.cache/zig --name test -I /home/vsts/work/1/s/test --override-lib-dir /home/vsts/work/1/s/lib 
error: the following build command failed with exit code 1:
/home/vsts/work/1/s/zig-cache/o/b44c2f8e472997c666788c7413e997b6/build /home/vsts/work/1/s/build/zig /home/vsts/work/1/s /home/vsts/work/1/s/zig-cache /home/vsts/.cache/zig test -Denable-qemu -Denable-wasmtime

[FireFox317]

The problem is in the getauxval function:

zig/lib/std/os/linux.zig

Lines 37 to 49 in 506af7e

	/// Set by startup code, used by `getauxval`.
	pub var elf_aux_maybe: ?[*]std.elf.Auxv = null;
	/// See `std.elf` for the constants.
	pub fn getauxval(index: usize) usize {
	const auxv = elf_aux_maybe orelse return 0;
	var i: usize = 0;
	while (auxv[i].a_type != std.elf.AT_NULL) : (i += 1) {
	if (auxv[i].a_type == index)
	return auxv[i].a_un.a_val;
	}
	return 0;
	}

As you can see the elf_aux_maybe is populated by the start.zig file and I'm pretty sure this startup code is not run when we do zig test. So it looks like we cannot test this (or somebody else knows a solution to this).

[LemonBoy]

Oh this is some other std.os bullshit, slap a if (builtin.link_libc) return error.SkipZigTest; and let's call it a day, this is a test for our direct syscall wrappers after all.