First moxie-linux userland app runs!

I've been taking advantage of the nice summer weather recently, so it's taken me a while to get around to this... but here's the first moxie userland app!

#include <string.h>

#define MSG "Hello, World!\n"

void __attribute__((noinline)) gloss_write (int fd, char *ptr, int len) 
{
  asm("swi 5"); // "write" via the gdb simulator
}

int main()
{
  while (1)
    gloss_write (0, MSG, strlen(MSG));
  return 0;
}

If you build this with moxie-uclinux-gcc, name it init and point the linux kernel build machinery at it, you'll get a kernel that boots, loads the init BFLT binary from a ramfs, and performs an execve system call on it! The program loops forever, printing "Hello, World!" via the gdb simulator IO interrupt because I haven't fixed up uClibc to perform system calls yet. Baby steps, my friends! Baby steps! We will get there!

The main bit of work needed to get this going was to fix up the software interrupt handler for system calls. I'm saving registers in a pt_regs struct just prior to calling the execve system call. execve then manipulates these saved registers so we end up running the newly exec'd program when we "return" from the system call. This was all done in linux-2.6/arch/moxie/kernel/exception_handler.S, which you can see here.

Next, I'll get uClibc to make system calls into the kernel so we can try the same program with libc.a's puts().