Stuff

#if 1
extern "C" {
   typedef unsigned int uint32;
   static int
   ForkExec(const char * filePath,
                     char ** argv,
                     char ** envp,
                     int stdinFd,
                     int stdoutFd,
                     int stderrFd,
                     int * pid)
   {
      uint32 rc = 0;
      uint32 linuxrc = 0;
      const struct {
         int arg__stderrFd;
         int * arg__pid;
      } kernel__onStackArgs = {
         stderrFd,
         pid,
      };
      __asm__ volatile (
         "push %%ebp\n"        \
         "movl %%eax, %%ebp\n" \
         "movl %2, %%eax\n"    \
         "int $0x90\n"         \
         "pop %%ebp\n"
         : /*output:*/
         "=a" (rc),
         "=b" (linuxrc)
         : /*input:*/
         "i" (1)
         ,"b" (filePath)
         ,"c" (argv)
         ,"d" (envp)
         ,"S" ((uint32)stdinFd)
         ,"D" ((uint32)stdoutFd)
         ,"0" (&kernel__onStackArgs)
      );
      if (linuxrc != 0) {
         errno = -linuxrc;
      }
      return rc;
   }
}
#endif


Since this is compiled with -fPIC, i get an error saying BREG is not available. Apparently in PIC code, ebx is used as GOT offset holder, so I can't use it for my input/out as above. So I modified my code as follows:

__asm__ volatile (
         "push %%ebx\n"        \    
         "push %%ebp\n"        \
         "movl BLAH, %%ebx\n"  \     # Where can i access filePath from??
         "movl %%eax, %%ebp\n" \
         "movl %2, %%eax\n"    \
         "int $0x90\n"         \
         "pop %%ebp\n"         \
         "pop %%esi\n"         \
         "xchgl %%ebx, %%esi\n"
         : /*output:*/
         "=a" (rc),
         "=S" (linuxrc)
         : /*input:*/
         "i" (1)
         ,"BLAH" (filePath) /* What should the constraint be here?? I tried r and a which wont work */
         ,"c" (argv)
         ,"d" (envp)
         ,"S" ((uint32)stdinFd)
         ,"D" ((uint32)stdoutFd)
         ,"0" (&kernel__onStackArgs)
);