Add read support for AArch64

arch/aarch64.c

@@ -33,6 +33,26 @@ intptr_t write(int32_t fd, const void* buf, intptr_t size){
   return n_written;
 }
 
+intptr_t read(int32_t fd, const void* buf, intptr_t size){
+  intptr_t n_read = 0;
+  asm volatile( 
+    // Assembly Instructions
+    "mov x0, %1\n"  // Set x0 to value of fd
+    "mov x1, %2\n"  // Set x1 to value of buf
+    "mov x2, %3\n"  // Set x2 to value of size
+    "mov x8, #63\n" // Syscall number for 'read' is 63 in AArch64
+    "svc #0\n"      // Make syscall
+    "mov %0, x0\n"  // Store return value in n_read
+    // Output operands
+    : "=r"(n_read)
+    // Input operands
+    : "r"((int64_t)fd), "r" (buf), "r"(size)
+    // Clobbered registers
+    : "x0", "x1", "x2", "x8"
+  );
+  return n_read;
+}
+
 #define CLONE_CHILD_SETTID   0x1000000
 #define CLONE_CHILD_CLEARTID 0x200000
 uint32_t fork(){

buildtest.c

@@ -25,7 +25,7 @@ int main() {
   if(pid == 0) return 0;
   //TODO: wait on child to remove zombie process
 
-  #if defined(__x86_64__)
+  #if defined(__x86_64__) || defined(__aarch64__)
   // Test the read syscall
   #define INPUT_BUFFER_LEN 4096
   char input_buffer[INPUT_BUFFER_LEN] = {0};

sys.h

@@ -6,7 +6,7 @@ void exit(int8_t status);
 #define STDIO 1
 #define STDERR 2
 intptr_t write(int32_t fd, const void* buf, intptr_t size);
-#if defined(__x86_64__)
+#if defined(__x86_64__) || defined(__aarch64__)
 intptr_t read(int32_t fd, const void* buf, intptr_t size);
 #endif