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

[Ivan Medoedov via llvm-dev]

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
>>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20190504/709016ab/attachment.html>