This post describes how to build software that will run on openwrt. Or more generally, it's a post about how to cross-compile for MIPS architecture.
My goal was to build a hello-world C app on my mac (64bit x86 arch.) for my openwrt router (MIPS arch.). This is called cross-compiling: building for one arch. on another.
In theory it's simple: you just past gcc the
-mach argument for the arch. you want:
gcc -march=i386 -o MyProgram sourcefile.c
However, this depends on what arch's you included when you built your gcc. I want to build for my router which is a MIPS arch. This didn't come w/ my gcc.
An easy way to get a compatible gcc for openwrt is to use the openwrt buildroot: http://wiki.openwrt.org/doc/howto/build This will get you all the tools you need. It builds gcc, binutils, etc -- your whole tool chain. If you look in you openwrt build dir in:
staging/bin/ you'll see a gcc that's build just for your arch. In my case MIP.
Then just build it like normal:
$ mipsel-openwrt-linux-uclibc-gcc hello.c -o hello_mips
Now check the arch:
$ file hello_mips hello_mips: ELF 32-bit MSB executable, MIPS, MIPS32 rel2 version 1, dynamically linked (uses shared libs), with unknown capability 0x41000000 = 0xf676e75, with unknown capability 0x10000 = 0x70403, not stripped
Now I can copy this binary to my router and run it:
$ ./hello_mips Hello, World!