Re: Linking mips .o files compiled with different -march= settings

[Matt Turner <mattst88 at gmail dot com>]

On Sun, Sep 16, 2012 at 11:38 AM, Matt Turner <mattst88@gmail.com> wrote:
> I've written some SIMD-optimized code for pixman
> (http://cgit.freedesktop.org/pixman/) that works on the Loongson MIPS
> CPU. There are different (mutually incompatible) revisions of the CPU:
> 2E and 2F. gcc provides no -m<flag> to turn on just the vectorization
> instructions like -msse or -mmmx on x86, so the only way to enable
> them is with -march=loongson2{e,f}.
>
> I'd like to compile my single source file with different -march=
> settings, provide different function entry-points, and link the
> resulting .o files into the main library which can do runtime
> selection to pick which code to use.
>
> It seems as if ld cannot link object code files that have been
> compiled with -march=loongson2e and -march=loongson2f together though.
> See the attached test case.
>
> cc -O2 -march=loongson2e -c ls2e.c -o ls2e.o
> cc -O2 -march=loongson2f -c ls2f.c -o ls2f.o
> cc -shared ls2e.o ls2f.o -o test.so
> /usr/lib/gcc/mips64el-unknown-linux-gnu/4.6.2/../../../../mips64el-unknown-linux-gnu/bin/ld:
> ls2e.o: linking mips:loongson_2e module with previous mips:loongson_2f
> modules
> /usr/lib/gcc/mips64el-unknown-linux-gnu/4.6.2/../../../../mips64el-unknown-linux-gnu/bin/ld:
> failed to merge target specific data of file ls2e.o
> collect2: ld returned 1 exit status
> make: *** [test.so] Error 1
>
> I'm using gcc-4.6.2 and binutils-2.22.
>
> Is there a reason why what I planned to do with pixman wouldn't work
> -- is there a real problem that binutils is preventing me from running
> into by rejecting the link?
>
> My pixman build system patch is available here:
> http://lists.freedesktop.org/archives/pixman/2012-September/002249.html
>
> Thanks,
> Matt

Actually, it seems even worse than this. My (Gentoo) system is
compiled with -march=loongson2f, which actually means that I cannot
even link the simplest program compiled with -march=loongson2e. This
cannot be intended, can it?