[llvm-bugs] [Bug 49799] New: LLD cannot link against iPhoneSimulator libSystem in Xcode 12 and newer

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=49799

            Bug ID: 49799
           Summary: LLD cannot link against iPhoneSimulator libSystem in
                    Xcode 12 and newer
           Product: lld
           Version: unspecified
          Hardware: PC
                OS: All
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: MachO
          Assignee: unassignedbugs at nondot.org
          Reporter: smeenai at fb.com
                CC: gkm at fb.com, jezreel at gmail.com,
                    llvm-bugs at lists.llvm.org, smeenai at fb.com

$ cat null.s
.globl _main
_main:
        retq

$ llvm-mc -filetype obj -triple x86_64-apple-ios14.0.0-simulator \
    -o null.o null.s
$ ld64.lld -platform_version ios-simulator 14.0.0 14.0 -arch x86_64 \
    -o null null.o -lSystem -syslibroot \
   
/Applications/Xcode_12.0.0.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator.sdk
ld64.lld: error:
/Applications/Xcode_12.0.0.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator.sdk/usr/lib/system/libsystem_kernel.tbd(/usr/lib/system/libsystem_kernel.dylib)
is incompatible with x86_64 (iOS Simulator)
ld64.lld: error:
/Applications/Xcode_12.0.0.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator.sdk/usr/lib/system/libsystem_platform.tbd(/usr/lib/system/libsystem_platform.dylib)
is incompatible with x86_64 (iOS Simulator)
ld64.lld: error:
/Applications/Xcode_12.0.0.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator.sdk/usr/lib/system/libsystem_pthread.tbd(/usr/lib/system/libsystem_pthread.dylib)
is incompatible with x86_64 (iOS Simulator)

Repros with 12.4 and 12.5 as well (and I presume other 12.x versions).

The error message seems legit, as far as I can tell. If I look at the
iPhoneSimulator libSystem.tbd, libsystem_kernel indeed doesn't have
x86_64-ios-simulator in its targets list. However, it's re-exported by
libsystem_sim_kernel_host, which does mark it as a re-export for the
x86_64-ios-simulator target (potentially a bug?). libsystem_sim_kernel_host is
re-exported by libsystem_sim_kernel, which is re-exported by libSystem, which
is presumably how we end up with the error.

ld64 is able to handle this libSystem. Interestingly enough, even if I force a
reference to __kernelrpc_mach_port_destroy_trap, which is not defined for
x86_64-ios-simulator (but is defined for x86_64-macos), it's able to link. The
link does fail if I reference ___aio_suspend, which is only defined for
i386-macos. I don't know if ld64 is specifically treating ios-simulator and
macos as equivalent, or if it's only looking at the architecture and not the
platform in general.

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