[llvm-dev] Problems generating Mach-O File (x86_64 , osx 10.12)

Jean-Daniel via llvm-dev llvm-dev at lists.llvm.org
Fri Jul 14 02:58:32 PDT 2017

LLD Mach-O support was experimental and AFAIK it is unmaintained. It lacks a lots of features to be usable. The only supported linker on macOS is ld64.

> Le 10 juil. 2017 à 17:36, Patricio Villalobos via llvm-dev <llvm-dev at lists.llvm.org> a écrit :
> I discovered that lld for darwin is generating the wrong code for lazy bindings in the __stub_helper section (at least for osx 10.12). This is the way i can reproduce this problem, using this program:
> program:
> #include <stdio.h>
> int main(int argc, char **argv) {
>     printf("C: printf!\n");
>     puts("C: puts!\n");
>     return 0;
> }
> Then I link it using i have tested it in 3.9, 4.0 and 4.1 versions:
> clang -c hello.c
> lld -flavor darwin hello.o -o h1  -lc
> When i execute the binary h1 the system gives me the following error:
> C: printf!
> dyld: lazy symbol binding failed: BIND_OPCODE_SET_SEGMENT_AND_OFFSET_ULEB has segment 4 which is too large (0..3)
> dyld: BIND_OPCODE_SET_SEGMENT_AND_OFFSET_ULEB has segment 4 which is too large (0..3)
> Trace/BPT trap: 5
> Investigating the code, it seems that the problem is that the asm code generated in the file StubPass.cpp, specifically in the line 323 <https://github.com/llvm-mirror/lld/blob/master/lib/ReaderWriter/MachO/StubsPass.cpp#L323> ,when it adds, what it seems an arbitrary number (12) to the offset into the lazy bind opcodes section, but it should be calculated depending on the MachONormalizedFileBinaryWrite::lazyBindingInfo result.
> I confirmed this bug by patching the code manually in the binary and writing the right offset in the asm code (__stub_helper). I'm yet not familiarized with the code , so i can't fix it right now , Im unable to find the information of the symbols that MachONormalizedFileBinaryWrite::buildLazyBindInfo has ,since is generated after the pass.
> I'll be glad to receive guidance so i can fix it myself and familiarize myself with the code.
> -- 
> Patricio
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