Add read support for mips

arch/mips.c

@@ -28,7 +28,21 @@ 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 read(int32_t fd, const void* buf, intptr_t size){
+  intptr_t n_read = 0;
+  asm volatile ( 
+    "move $a0, %1\n"
+    "move $a1, %2\n"
+    "move $a2, %3\n"
+    "li $v0, 4004\n"
+    "syscall\n"
+    "move %0, $v0\n"
+    : "=r"(n_read)
+    : "r"(fd), "r"(buf), "r"(size)
+    : "a0", "a1", "a2", "v0" //TODO: temp registers clobbered by syscall should probably also be listed but this fn returns right away so it should be fine?
+  );
+  return n_read;
+}
 
 uint32_t fork(){
   int rtn;

buildtest.c

@@ -25,14 +25,12 @@ int main() {
   if(pid == 0) return 0;
   //TODO: wait on child to remove zombie process
 
-  #if defined(__x86_64__) || defined(__aarch64__)
   // Test the read syscall
   #define INPUT_BUFFER_LEN 4096
   char input_buffer[INPUT_BUFFER_LEN] = {0};
   write(STDIO, "Enter some text:", 16);
   intptr_t n_read = read(STDIO, input_buffer, INPUT_BUFFER_LEN);
   write(STDIO, input_buffer, n_read);
-  #endif
 
   return 69;
 }

sys.h

@@ -6,9 +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__) || defined(__aarch64__)
 intptr_t read(int32_t fd, const void* buf, intptr_t size);
-#endif
 
 uint32_t fork();