How can I cross-compile C code for a Cyrix Cx486DX?

Question

The question says it all. I need to cross-compile for a Cyrix CPU. The system the compiler (doesn't have to be gcc) needs to run on is a 64bit Kubuntu, with an i5 processor. I couldn't find anything useful googling, except for a piece of information saying that "Cx486DX is software-compatible with i486". So I ran

gcc -m32 -march=i486 helloworld.c -o helloworld486.bin

but executing helloworld486.bin on the Cyrix machine gives me a floating point exception. My knowledge about CPUs is rather limited and I'm out of ideas now, any help would be really appreciated.

Answer 1

Unfortunately you need more than just a compiler that generates instructions for the 486. The compiler libraries, as well as any libraries that are linked in statically should be suitable as well. The GCC version included in most current Linux distributions is able to generate 486-only object files (I think), but its libraries and stub objects (e.g. crtbegin.o) have been pre-generated for 686 CPUs.

There are two main alternatives here:

• Use a Linux build system that is compiled for 486 itself, either in a VM or in a chroot jail. Unfortunately getting a modern Linux distribution for the 486 is a bit of an issue - every single major distribution has moved on. Perhaps a (much) older Linux distribution would be of help?

• Create a full cross-compiler toolchain for the 486. You can then cross-compile separate versions of all needed libraries and have your build scripts use them. Quite honestly, ensuring that nothing from the (usually 686-based) build host slips through to the build result is not very easy. It oftens amounts to cross-compiling a whole Linux system from scratch, ala CLFS.

  An automated cross-compiler toolchain build script, such as crosstool-ng might be of help.

Could you add more details about your target system? Is it an embedded system or just an old PC? What OS is it using? Would it be possible to just run your compile in a VM with a version of the target OS?