Build 32-bit with 64-bit llvm-gcc

Question

I have a 64-bit version of llvm-gcc, but I want to be able to build both 32-bit and 64-bit binaries. Is there a flag for this? I tried passing -m32 (which works on the regular gcc), but I get an error message like this:

[jay@andesite]$ llvm-gcc -m32 test.c -o test
Warning: Generation of 64-bit code for a 32-bit processor requested.
Warning: 64-bit processors all have at least SSE2.
/tmp/cchzYo9t.s: Assembler messages:
/tmp/cchzYo9t.s:8: Error: bad register name `%rbp'
/tmp/cchzYo9t.s:9: Error: bad register name `%rsp'
...

This is backwards; I want to generate 32-bit code for a 64-bit processor!

I'm running llvm-gcc 4.2, the one that comes with Ubuntu 9.04 x86-64.

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EDIT: Here is the relevant part of the output when I run llvm-gcc with the -v flag:

[jay@andesite]$ llvm-gcc -v -m32 test.c -o test.bc
Using built-in specs.
Target: x86_64-linux-gnu
Configured with: ../llvm-gcc4.2-2.2.source/configure --host=x86_64-linux-gnu --build=x86_64-linux-gnu --prefix=/usr/lib/llvm/gcc-4.2 --enable-languages=c,c++ --program-prefix=llvm- --enable-llvm=/usr/lib/llvm --enable-threads --disable-nls --disable-shared --disable-multilib --disable-bootstrap
Thread model: posix
gcc version 4.2.1 (Based on Apple Inc. build 5546) (LLVM build)
 /usr/lib/llvm/gcc-4.2/libexec/gcc/x86_64-linux-gnu/4.2.1/cc1 -quiet -v -imultilib . test.c -quiet -dumpbase test.c -m32 -mtune=generic -auxbase test -version -o /tmp/ccw6TZY6.s

I looked in /usr/lib/llvm/gcc-4.2/libexec/gcc hoping to find another binary, but the only directory there is x86_64-linux-gnu. I will probably look at compiling llvm-gcc from source with appropriate options next.

Answer 1

Try setting:

export CFLAGS="-m32"
export LDFLAGS="-m32"

before compiling...

Answer 2

Could you try this series of commands and see if it works? Theoretically if you provided llvm-gcc with the -m32 option these steps should be taken by llvm-gcc, but maybe it's not working correctly, so let's make all the steps explicit:

llvm-gcc -m32 -emit-llvm test.c -c -o test.bc
llc test.bc -march=x86 -o test.S
gcc test.S -m32 -o test

This should be the sequence of steps (or something similar) that llvm-gcc performs implicitly, but it looks like in your case it's emitting 64bit assembly for some reason, then trying to assemble and link it for 32bit.

Answer 3

I had the same problem, llvm-gcc ignores the flags, the only solution that worked was to switch from llvm-gcc to clang which does respect the -m32. That or switch to a 32 bit operating system for llvm-gcc work.