Add waitpid and execve

arch/mips.c

@@ -1,5 +1,19 @@
 #if defined(__mips__)
 #include "../int.h"
+#include "../sys.h"
+
+/*
+#ifndef _START_DEFINED
+#define _START_DEFINED
+extern int main(int c, char** v);
+void __start() {
+  void* fp = __builtin_frame_address(0);
+  register int argc asm("a0") = *(uintptr_t*)(fp+32);
+  register char** argv asm("a1") = fp+36;
+  exit(main(argc, argv));
+}
+
+#endif */ /* ifndef _START_DEFINED */
 
 #include "generic.h"
 
@@ -59,6 +73,37 @@ uint32_t fork(){
   return (uint32_t)rtn;
 }
 
+uint32_t waitpid(uint32_t pid, int* wstatus, int options) {
+  int child_pid = 0;
+  asm volatile ( 
+    "move $a0, %1\n"
+    "move $a1, %2\n"
+    "move $a2, %3\n"
+    "li $v0, 4007\n"
+    "syscall\n"
+    "move %0, $v0\n"
+    : "=r"(child_pid)
+    : "r"(pid), "r"(wstatus), "r"(options)
+    : "a0", "a1", "a2", "v0", "memory"
+  );
+  return child_pid;
+}
+
+int32_t execve(const char* filename, const char* argv[], const char* envp[]){
+  int rtn;
+  asm volatile (
+    "move $a0, %0\n"
+    "move $a1, %1\n"
+    "move $a2, %2\n"
+    "li $v0, 4011\n"
+    "syscall\n"
+    : "=r"(rtn)
+    : "r"(filename), "r"(argv), "r"(envp)
+    : "a0", "a1", "a2", "a3", "v0"
+  );
+  return (int32_t)rtn;
+}
+
 int32_t openat(int32_t fd, const char* filename, uint32_t flags, uint32_t mode) {
   int32_t file = 0;
   asm volatile (