Add x86_64 start code to access argc and argv

arch/x86_64.c

@@ -1,8 +1,25 @@
 #if defined(__x86_64__)
 #include "../int.h"
+#include "../sys.h"
 
+// Start code
+#ifndef _START_DEFINED
+#define _START_DEFINED
+extern int main(int argc, char** argv);
+void _start() {
+  void* fp = __builtin_frame_address(0);
+  register int argc asm("rdi") = *(uint64_t*)(fp+8);
+  register char** argv asm("rsi") = fp+16;
+  exit(main(argc, argv));
+}
+#endif /* ifndef _START_DEFINED */
+
+//include other generic functions
 #include "generic.h"
 
+//
+// syscall functions
+
 #define SYS_EXIT 60
 void exit(int8_t status) {
   asm volatile(
@@ -243,4 +260,17 @@ int clock_nanosleep(clockid_t clockid, int flags, const struct timespec *t, stru
   return rtn;
 }
 
+#define SYS_RT_SIGACTION 13
+int rt_sigaction(int signum, const void* act, void* oldact, size_t sigset_len) {
+  int rtn;
+  asm volatile(
+    "mov %5, %%r10\n"
+    "syscall\n"
+    : "=a"(rtn)
+    : "a"(SYS_RT_SIGACTION), "D"(signum), "S"(act), "d"(oldact), "r"(sigset_len)
+    : "rcx", "r11", "memory"
+  );
+  return rtn;
+}
+
 #endif /* ifdef __x86_64__ */