How to create a 32-bit shared-library on a 64-bit platform with autotools
I'm using autotools to build my system, which consists primarily of a library. On 64-bit Red Hat platforms, I need to be able to produce a library capable of working on 32-bit Red Hat platforms.
When I add -m32 to the compile lines everything works fine to produce a static (.a) library, but as soon as I try to create a shared-library, I get error like this:
/usr/bin/ld: warning: i386:x86-64 architecture of input file `/usr/lib/gcc/x86_64-redhat-linux/4.1.2/../../../../lib64/crti.o' is incompatible with i386 output
/usr/bin/ld: warning: i386:x86-64 architecture of input file `/usr/lib/gcc/x86_64-redhat-linux/4.1.2/crtbeginS.o' is incompatible with i386 output
/usr/lib/gcc/x86_64-redhat-linux/4.1.2/crtbeginS.o: In function `__do_global_dtors_aux':
crtstuff.c:(.text+0x29): undefined reference to `__DTOR_END__'
collect2: ld returned 1 exit status'
I can see the problem is that it's including 64-bit object files out of /usr/lib64 instead of the correct 32-bit ones out of /usr/lib (they're there alright), but I can't figure out how to fix it.
Answer
First, make sure you have compiler/libc support for 32-bit compilation. In some distros like Ubuntu, what you need to do is install packages gcc-multilib and/or g++-multilib:
sudo apt-get install gcc-multilib g++-multilib
Then, when calling configure, specify a 32-bit host and pass 32-bit compilation flags:
./configure --host=i686-linux-gnu "CFLAGS=-m32" "CXXFLAGS=-m32" "LDFLAGS=-m32"
If you do not have multilib installed, you will get an error like configure: error: C compiler cannot create executables when passing the -m32 flag.