[llvm-dev] Cross compiling an empty program results in a segfault

[Ivan Medoedov via llvm-dev]

I managed to do it with

ld.lld -v -o hi -m elf_x86_64 -dynamic-linker \
 /lib64/ld-linux-x86-64.so.2 \
 /usr/lib/x86_64-linux-gnu/crt1.o \
 /usr/lib/x86_64-linux-gnu/crti.o \
 hi_lin.o \
 /usr/lib/x86_64-linux-gnu/libc.so \
 /usr/lib/x86_64-linux-gnu/crtn.o

I had to create  /usr/lib/x86_64-linux-gnu/ directory on my Mac and copy
about 8 libc files. This felt like a hack, but it worked.


On Sat, May 4, 2019 at 1:51 AM Ivan Medoedov <ivan.medoedov at gmail.com>
wrote:

> The reason I was trying to link it myself is because clang failed:
>
> ld: unknown option: --eh-frame-hdr
>
> My host is macOS, trying to compile for Linux:
>
> clang -target x86_64-pc-linux-gnu -o main_linux main.c
>
> main.c is an empty program with 0 dependencies.
>
> On Sat, May 4, 2019 at 1:43 AM Ivan Medoedov <ivan.medoedov at gmail.com>
> wrote:
>
>> Sorry for the late reply.
>>
>> Thanks, Eli. That was really helpful.
>>
>> On Fri, Apr 12, 2019 at 9:31 PM Eli Friedman <efriedma at quicinc.com>
>> wrote:
>>
>>> “--entry main” is not going to do what you want; the entry point for a
>>> Linux program is not equivalent to the C “main”.
>>> http://dbp-consulting.com/tutorials/debugging/linuxProgramStartup.html
>>> has a description of how a C program normally starts on Linux.
>>>
>>>
>>>
>>> Generally, to build a C program, you don’t want to invoke the linker
>>> directly; instead, use clang to invoke the linker correctly.  This will
>>> pass the appropriate flags and link against the appropriate libraries.
>>> When you’re cross compiling, to make this work, you have to actually have
>>> the appropriate libraries, so you’ll have to build or download them
>>> separately.  Then you tell clang the path to those libraries using
>>> –sysroot.  https://clang.llvm.org/docs/CrossCompilation.html has a
>>> general description of various issues with cross-compiling.
>>>
>>>
>>>
>>> -Eli
>>>
>>>
>>>
>>> *From:* llvm-dev <llvm-dev-bounces at lists.llvm.org> *On Behalf Of *Ivan
>>> Medoedov via llvm-dev
>>> *Sent:* Wednesday, April 10, 2019 1:28 PM
>>> *To:* llvm-dev at lists.llvm.org
>>> *Subject:* [EXT] [llvm-dev] Cross compiling an empty program results in
>>> a segfault
>>>
>>>
>>>
>>> Hello,
>>>
>>>
>>>
>>> I'm trying to cross compile an empty program on macOS for Linux:
>>>
>>>
>>>
>>> cat test.c
>>>
>>>
>>>
>>> int main() {
>>>
>>>         int a = 2+3;
>>>
>>>         return 0;
>>>
>>> }
>>>
>>>
>>>
>>> clang -o -c -target x86_64-linux-gnu test.c
>>>
>>>
>>>
>>> If I copy the resulting test.o to the Linux machine and run clang
>>> test.o, it works fine.
>>>
>>>
>>>
>>> However if I try to link it on macOS, I get a segfault when I launch
>>> ./a.out
>>>
>>>
>>>
>>> ld.lld --entry main test.o
>>>
>>>
>>>
>>> [copy a.out to Linux]
>>>
>>>
>>>
>>> ./a.out
>>>
>>> segmentation fault 0x00000000001 in ?? ()
>>>
>>>
>>>
>>> Would really appreciate your help here!
>>>
>>>
>>>
>>> Thanks
>>>
>>
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