Add read support for x86_64

arch/x86_64.c

@@ -1,34 +1,50 @@
 #include <stdint.h>
 #if defined(__x86_64__)
 
+#define SYS_EXIT 60
 void exit(int8_t status) {
   asm volatile(
     "syscall"
     :
-    : "a"(60), "D"(status)
+    : "a"(SYS_EXIT), "D"(status)
     :
     );
 }
 
+#define SYS_WRITE 1
 intptr_t write(int32_t fd, const void* buf, intptr_t size) {
   intptr_t n_written = 0;
   asm volatile (
       "syscall\n"
       "movq %0, %%rax\n"
       : "=r"(n_written)
-      : "a"(1), "D"(fd), "S"(buf), "d"(size)  // RDI, RSI, RDX are used in x86-64 for write args
+      : "a"(SYS_WRITE), "D"(fd), "S"(buf), "d"(size)  // RDI, RSI, RDX are used in x86-64 for write args
       : "rcx", "r11", "memory"
   );
   return n_written;
 }
 
+#define SYS_READ 0
+intptr_t read(int32_t fd, const void* buf, intptr_t size) {
+  intptr_t n_read = 0;
+  asm volatile (
+      "syscall\n"
+      "movq %0, %%rax\n"
+      : "=r"(n_read)
+      : "a"(SYS_READ), "D"(fd), "S"(buf), "d"(size)  // RDI, RSI, RDX are used in x86-64 for write args
+      : "rcx", "r11", "memory"
+  );
+  return n_read;
+}
+
+#define SYS_FORK 57
 uint32_t fork() {
   uint64_t rtn;
   asm volatile(
     "syscall\n"         // syscall
     "movq %0, %%rax\n"    // save return value
     : "=r"(rtn)
-    : "a"(57)
+    : "a"(SYS_FORK)
     :
   );
   return (uint32_t)rtn;