panic: index out of bounds in link.MachO.ZldAtom.resolveRelocsArm64

[winterqt]

Zig Version

0.10.1

Steps to Reproduce and Observed Behavior

After fixing the @alignCast issue in #14558, stage3 fails to build on aarch64-darwin with a different error:

thread 666841 panic: index out of bounds
/private/tmp/nix-build-zig-0.10.1.drv-0/source/src/link/MachO/ZldAtom.zig:793:53: 0x105a2bd27 in link.MachO.ZldAtom.resolveRelocsArm64 (zig2)
                    mem.readIntLittle(i64, atom_code[rel_offset..][0..8])
                                                    ^
/private/tmp/nix-build-zig-0.10.1.drv-0/source/src/link/MachO/ZldAtom.zig:483:39: 0x105a2719f in link.MachO.ZldAtom.resolveRelocs (zig2)
        .aarch64 => resolveRelocsArm64(zld, atom_index, atom_code, atom_relocs, reverse_lookup, ctx),
                                      ^
/private/tmp/nix-build-zig-0.10.1.drv-0/source/src/link/MachO/zld.zig:1736:43: 0x1056db723 in link.MachO.zld.Zld.writeAtoms (zig2)
                    try Atom.resolveRelocs(
                                          ^
/private/tmp/nix-build-zig-0.10.1.drv-0/source/src/link/MachO/zld.zig:4290:27: 0x10545e997 in link.MachO.zld.linkWithZld (zig2)
        try zld.writeAtoms(reverse_lookups);
                          ^
/private/tmp/nix-build-zig-0.10.1.drv-0/source/src/link/MachO.zig:427:44: 0x10519e6d7 in link.MachO.flush (zig2)
        .one_shot => return zld.linkWithZld(self, comp, prog_node),
                                           ^
/private/tmp/nix-build-zig-0.10.1.drv-0/source/src/link.zig:797:72: 0x10519b4b3 in link.File.flush (zig2)
            .macho => return @fieldParentPtr(MachO, "base", base).flush(comp, prog_node),
                                                                       ^
/private/tmp/nix-build-zig-0.10.1.drv-0/source/src/Compilation.zig:2516:24: 0x105114a87 in Compilation.flush (zig2)
    comp.bin_file.flush(comp, prog_node) catch |err| switch (err) {
                       ^
/private/tmp/nix-build-zig-0.10.1.drv-0/source/src/Compilation.zig:2480:27: 0x105107bbf in Compilation.update (zig2)
            try comp.flush(main_progress_node);
                          ^
/private/tmp/nix-build-zig-0.10.1.drv-0/source/src/main.zig:3361:20: 0x1050898af in main.updateModule (zig2)
    try comp.update();
                   ^
/private/tmp/nix-build-zig-0.10.1.drv-0/source/src/main.zig:3028:17: 0x104fc60f7 in main.buildOutputType (zig2)
    updateModule(gpa, comp, hook) catch |err| switch (err) {
                ^
/private/tmp/nix-build-zig-0.10.1.drv-0/source/src/main.zig:230:31: 0x104f4efc3 in main.mainArgs (zig2)
        return buildOutputType(gpa, arena, args, .{ .build = .Exe });
                              ^
/private/tmp/nix-build-zig-0.10.1.drv-0/source/src/stage1.zig:56:24: 0x104f4e8fb in main (zig2)
        stage2.mainArgs(gpa, arena, args) catch unreachable;
                       ^

Expected Behavior

For it to link correctly :)

[andrewrk]

@kubkon would you mind taking a look at this? It is reported against 0.10.1 but I believe the issue may still be present in master branch. @winterqt is working on packaging zig 0.10.1 for nixpkgs and has run into this problem. It would behoove us and our users if we could provide a workaround patch for nixpkgs to carry to resolve this issue until they can update to 0.11.0.

[winterqt]

(This should get the os-macos label.)

[kubkon]

Sure, but I need more than just a panic stack trace :-) Are there any steps I could follow to even try and repro the issue locally? Otherwise, it's not much to go on sadly.

[kubkon]

Here's my hunch at what is happening. Packaging for nixpgks generates an object file with a funky looking symtab which is then packaged into archive and put on the linker link as per #14558. This manifests itself as an alignment panic, which if circumvented (downgraded to align(1)) advanced the linker further and fails with out-of-bounds access when pulling relocations for some subsection from that object file which are not there, or for whatever reason. If it was possible for me to repro the issue, or at the very least to learn which archive/object file causes the original alignment panic and have it available for inspection, I should be able to fix the issue relatively quickly.

[kubkon]

(Oops, apologies for accidentally closing the issue!)

[winterqt]

@kubkon You can reproduce this by installing Nix, cloning Nixpkgs, and running NIXPKGS_ALLOW_BROKEN=1 nix-build -A zig_0_10. You can add patches by adding patches = [ ./foo.nix ] to pkgs/development/compilers/zig/0.10.nix, where foo.nix is in pkgs/development/compilers/zig.

If you'd rather not install Nix, let me know -- I have a machine I can give you access to that has it installed.

If there's anything that you need further clarification on, let me know, and thank you both for helping us out.

[kubkon]

Nice, thank you so much for the repro! I'll get right on it!

[kubkon]

Is there any trick into getting nix to find the includes? I am getting this currently:

/tmp/nix-build-zig-0.10.1.drv-0/source/lib/libcxx/include/stdlib.h:93:15: fatal error: 'stdlib.h' file not found

Perhaps an env var I need to set or something?

[winterqt]

Hmm, I haven't run into that.

What modifications did you make, if any, or is this a clean tree? Also, just to be sure, this is on aarch64, and not x86_64, right?