How to compile a 32bit hello world on alpine? - c

Question

Given a simple hello world code:
#include <stdio.h>
int main(void){
puts("hello");
return 0;
}
On a 64bit alpine linux installation I tried to compile it as 64bit and as 32bit.
The first works fine, but the second is missing 32bit libraries:
~ # gcc -Wall hello.c
~ # gcc -Wall -m32 hello.c
/usr/lib/gcc/x86_64-alpine-linux-musl/5.3.0/../../../../x86_64-alpine-linux-musl/bin/ld: skipping incompatible /usr/lib/gcc/x86_64-alpine-linux-musl/5.3.0/../../../libssp_nonshared.a when searching for -lssp_nonshared
/usr/lib/gcc/x86_64-alpine-linux-musl/5.3.0/../../../../x86_64-alpine-linux-musl/bin/ld: skipping incompatible //usr/lib/libssp_nonshared.a when searching for -lssp_nonshared
/usr/lib/gcc/x86_64-alpine-linux-musl/5.3.0/../../../../x86_64-alpine-linux-musl/bin/ld: cannot find -lssp_nonshared
/usr/lib/gcc/x86_64-alpine-linux-musl/5.3.0/../../../../x86_64-alpine-linux-musl/bin/ld: skipping incompatible /usr/lib/gcc/x86_64-alpine-linux-musl/5.3.0/libgcc.a when searching for -lgcc
/usr/lib/gcc/x86_64-alpine-linux-musl/5.3.0/../../../../x86_64-alpine-linux-musl/bin/ld: cannot find -lgcc
/usr/lib/gcc/x86_64-alpine-linux-musl/5.3.0/../../../../x86_64-alpine-linux-musl/bin/ld: skipping incompatible /usr/lib/gcc/x86_64-alpine-linux-musl/5.3.0/../../../libgcc_s.so when searching for -lgcc_s
/usr/lib/gcc/x86_64-alpine-linux-musl/5.3.0/../../../../x86_64-alpine-linux-musl/bin/ld: skipping incompatible //usr/lib/libgcc_s.so when searching for -lgcc_s
/usr/lib/gcc/x86_64-alpine-linux-musl/5.3.0/../../../../x86_64-alpine-linux-musl/bin/ld: cannot find -lgcc_s
/usr/lib/gcc/x86_64-alpine-linux-musl/5.3.0/../../../../x86_64-alpine-linux-musl/bin/ld: skipping incompatible /usr/lib/gcc/x86_64-alpine-linux-musl/5.3.0/../../../libc.so when searching for -lc
/usr/lib/gcc/x86_64-alpine-linux-musl/5.3.0/../../../../x86_64-alpine-linux-musl/bin/ld: skipping incompatible /usr/lib/gcc/x86_64-alpine-linux-musl/5.3.0/../../../libc.a when searching for -lc
/usr/lib/gcc/x86_64-alpine-linux-musl/5.3.0/../../../../x86_64-alpine-linux-musl/bin/ld: skipping incompatible //usr/lib/libc.so when searching for -lc
/usr/lib/gcc/x86_64-alpine-linux-musl/5.3.0/../../../../x86_64-alpine-linux-musl/bin/ld: skipping incompatible //usr/lib/libc.a when searching for -lc
/usr/lib/gcc/x86_64-alpine-linux-musl/5.3.0/../../../../x86_64-alpine-linux-musl/bin/ld: cannot find -lc
/usr/lib/gcc/x86_64-alpine-linux-musl/5.3.0/../../../../x86_64-alpine-linux-musl/bin/ld: skipping incompatible /usr/lib/gcc/x86_64-alpine-linux-musl/5.3.0/libgcc.a when searching for -lgcc
/usr/lib/gcc/x86_64-alpine-linux-musl/5.3.0/../../../../x86_64-alpine-linux-musl/bin/ld: cannot find -lgcc
/usr/lib/gcc/x86_64-alpine-linux-musl/5.3.0/../../../../x86_64-alpine-linux-musl/bin/ld: skipping incompatible /usr/lib/gcc/x86_64-alpine-linux-musl/5.3.0/../../../libgcc_s.so when searching for -lgcc_s
/usr/lib/gcc/x86_64-alpine-linux-musl/5.3.0/../../../../x86_64-alpine-linux-musl/bin/ld: skipping incompatible //usr/lib/libgcc_s.so when searching for -lgcc_s
/usr/lib/gcc/x86_64-alpine-linux-musl/5.3.0/../../../../x86_64-alpine-linux-musl/bin/ld: cannot find -lgcc_s
collect2: error: ld returned 1 exit status
Because I found no obvious way to fix this, I fetched the 32bit version of gcc, libgcc, and musl-dev extracted to a local directory and set LIBRARY_PATH:
~ # LIBRARY_PATH=usr/lib/gcc/i586-alpine-linux-musl/5.3.0:usr/lib gcc -Wall -m32 hello.c
/usr/lib/gcc/x86_64-alpine-linux-musl/5.3.0/../../../../x86_64-alpine-linux-musl/bin/ld: skipping incompatible /usr/lib/gcc/x86_64-alpine-linux-musl/5.3.0/libgcc.a when searching for -lgcc
/usr/lib/gcc/x86_64-alpine-linux-musl/5.3.0/../../../../x86_64-alpine-linux-musl/bin/ld: skipping incompatible /usr/lib/gcc/x86_64-alpine-linux-musl/5.3.0/libgcc.a when searching for -lgcc
/usr/lib/gcc/x86_64-alpine-linux-musl/5.3.0/../../../../x86_64-alpine-linux-musl/bin/ld: i386:x86-64 architecture of input file `/usr/lib/gcc/x86_64-alpine-linux-musl/5.3.0/crtbeginS.o' is incompatible with i386 output
/usr/lib/gcc/x86_64-alpine-linux-musl/5.3.0/../../../../x86_64-alpine-linux-musl/bin/ld: i386:x86-64 architecture of input file `/usr/lib/gcc/x86_64-alpine-linux-musl/5.3.0/crtendS.o' is incompatible with i386 output
collect2: error: ld returned 1 exit status
~ #
This partly fixed the issues, but gcc still tries the 64bit libraries first and finds tries to find the 64bit crt files.
So what is the correct way to compile a 32bit binary on alpine linux?
To make the last problem more clear, look at this:
~ # LIBRARY_PATH=/tmp gcc --verbose -Wall -m32 hello.c 2>&1|grep LIBRARY_PATH
LIBRARY_PATH=/usr/lib/gcc/x86_64-alpine-linux-musl/5.3.0/:/tmp/:/usr/lib/gcc/x86_64-alpine-linux-musl/5.3.0/../../../../x86_64-alpine-linux-musl/lib/:/usr/lib/gcc/x86_64-alpine-linux-musl/5.3.0/../../../:/lib/:/usr/lib/
If I only set some LIBRARY_PATH, the compiler internally adds other directories to it. Especially it also prepends the "wrong" system directory, which contains the 64bit libraries. Therefore it uses the wrong crt libs and therefore the last error above.
I either need the correct alpine package (and not care about how it works), or I need to understand how to change that first path added internally by gcc.

Answer 1

According to gcc -v on alpine gcc is compiled without multilib support:
--disable-multilib
While multilib is enabled on debian:
--with-multilib-list=m32,m64,mx32 --enable-multilib
Multilib support is required for the -m32 to work reliable. Therefore the default compiler on alpine is really not suited for compiling 32bit binaries.