link/macho: segfault in dedupLiterals when using objc symbols

[slimsag]

Zig Version

0.14.0-dev.1710+8ee52f99c

Steps to Reproduce and Observed Behavior

We updated Mach to the latest Zig nightly version 0.14.0-dev.1710+8ee52f99c and found we were hitting a compiler segfault; I managed to create a minimal reproduction.

my macOS version: 14.1.1 (23B2082)

I do not have xcode installed:

% ls /Applications/Xcode.app
ls: /Applications/Xcode.app: No such file or directory

With this main.zig:

pub fn main() !void {
    const msg_send_fn = @extern(
        *const fn () callconv(.C) usize,
        .{ .name = "objc_msgSend$initWithContentRect:styleMask:backing:defer:screen:" },
    );
    _ = @call(
        .auto,
        msg_send_fn,
        .{},
    );
}

The following build-exe command segfaults:

% zig build-exe -ODebug -Mroot=./main.zig

zsh: segmentation fault  zig build-exe -ODebug -Mroot=./main.zig

Running under lldb shows the following:

% lldb -- zig build-exe -ODebug -Mroot=./main.zig
(lldb) target create "zig"
Current executable set to '/Users/slimsag/.bin/zig' (arm64).
(lldb) settings set -- target.run-args  "build-exe" "-ODebug" "-Mroot=./main.zig"
(lldb) run
Process 30140 launched: '/Users/slimsag/.bin/zig' (arm64)
Process 30140 stopped
* thread #1, queue = 'com.apple.main-thread', stop reason = EXC_BAD_ACCESS (code=1, address=0x14)
    frame #0: 0x0000000104fc9104 zig`link.MachO.dedupLiterals + 4960
zig`link.MachO.dedupLiterals:
->  0x104fc9104 <+4960>: ldur   x8, [x0, #0x14]
    0x104fc9108 <+4964>: lsr    x9, x8, #32
    0x104fc910c <+4968>: madd   x10, x25, x27, x20
    0x104fc9110 <+4972>: cmp    x25, #0x0
Target 0: (zig) stopped.
(lldb) bt
* thread #1, queue = 'com.apple.main-thread', stop reason = EXC_BAD_ACCESS (code=1, address=0x14)
  * frame #0: 0x0000000104fc9104 zig`link.MachO.dedupLiterals + 4960
    frame #1: 0x0000000104e47eb0 zig`link.MachO.flushModule + 21672
    frame #2: 0x0000000104cdd0d4 zig`Compilation.flush + 732
    frame #3: 0x0000000104ce30b4 zig`Compilation.update + 17308
    frame #4: 0x0000000104ce50d4 zig`main.updateModule + 44
    frame #5: 0x0000000104d2268c zig`main.buildOutputType + 89460
    frame #6: 0x0000000104c44048 zig`main + 3004
    frame #7: 0x00000001878bd0e0 dyld`start + 2360

Suspecting it is related to #20032

cc @kubkon

Expected Behavior

No compiler segfault.

[slimsag]

Updated issue description with an even simpler reproduction.

Also, because I know someone will ask, the extern name:

.name = "objc_msgSend$initWithContentRect:styleMask:backing:defer:screen:"

This is the extern name format that Objective C actually writes for a function like AppKit's function here: https://developer.apple.com/documentation/appkit/nswindow/1419477-initwithcontentrect

In mach-objc we have a code generator to invoke such functions, which boils down to an extern with that name - which you can see here and here for example.