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

[Andrew Kelley via llvm-dev]

On Jul 14, 2017 10:58, "Jean-Daniel via llvm-dev" <llvm-dev at lists.llvm.org>
wrote:

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.


Surely this is not the end-game?

Patricio has submitted a patch to fix this particular issue. Please let us
move LLD forward enough in the meantime until llvm devs consider mach-o a
first class target of LLD.


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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