Add support for openat on x86_64

arch/aarch64.c

@@ -48,7 +48,7 @@ intptr_t read(int32_t fd, const void* buf, intptr_t size){
     // Input operands
     : "r"((int64_t)fd), "r" (buf), "r"(size)
     // Clobbered registers
-    : "x0", "x1", "x2", "x8"
+    : "x0", "x1", "x2", "x8", "memory"
   );
   return n_read;
 }

arch/mips.c

@@ -39,7 +39,7 @@ intptr_t read(int32_t fd, const void* buf, intptr_t size){
     "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?
+    : "a0", "a1", "a2", "v0", "memory" //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;
 }

arch/x86_64.c

@@ -20,7 +20,7 @@ intptr_t write(int32_t fd, const void* buf, intptr_t size) {
       "movq %0, %%rax\n"
       : "=r"(n_written)
       : "a"(SYS_WRITE), "D"(fd), "S"(buf), "d"(size)  // RDI, RSI, RDX are used in x86-64 for write args
-      : "rcx", "r11", "memory"
+      : "rcx", "r11"
   );
   return n_written;
 }
@@ -50,4 +50,18 @@ uint32_t fork() {
   );
   return (uint32_t)rtn;
 }
+
+#define SYS_OPENAT 257
+int32_t openat(int32_t fd, const char* filename, uint32_t flags, uint32_t mode) {
+  int32_t file;
+  asm volatile (
+      "mov %%r10, %5\n"
+      "syscall\n"
+      : "=a"(file)
+      : "a"(SYS_OPENAT), "D"(fd), "S"(filename), "d"(flags), "r"((uint64_t)mode)  // RDI, RSI, RDX are used in x86-64 for write args
+      : "rcx", "r10", "r11"
+  );
+  return file;
+}
+
 #endif /* ifdef __x86_64__ */

buildtest.c

@@ -32,6 +32,15 @@ int main() {
   intptr_t n_read = read(STDIO, input_buffer, INPUT_BUFFER_LEN);
   write(STDIO, input_buffer, n_read);
 
+  // Test the open syscall
+  #if defined(__x86_64__)
+  int32_t file = open("/proc/version", O_RDONLY);
+  int i = read(file, input_buffer, INPUT_BUFFER_LEN);
+  while(i > 0) {
+    write(STDIO, input_buffer, i);
+    i = read(file, input_buffer, INPUT_BUFFER_LEN);
+  }
+  #endif
   return 69;
 }
 

sys.h

@@ -8,6 +8,16 @@ void exit(int8_t status);
 intptr_t write(int32_t fd, const void* buf, intptr_t size);
 intptr_t read(int32_t fd, const void* buf, intptr_t size);
 
+#define O_RDONLY       00
+#define O_WRONLY       01
+#define O_RDWR         02
+#define AT_FDCWD      -100
+int32_t openat(int32_t fd, const char* filename, uint32_t flags, uint32_t mode);
+#define open(...) openat(AT_FDCWD, __VA_ARGS__, 0)
+//inline int32_t openat(int32_t fd, const char* filename, uint32_t flags) {return openat(fd, filename, flags, 0);}
+//inline int32_t open(const char* filename, uint32_t flags, uint32_t mode) {return openat(AT_FDCWD, filename, flags, mode);}
+//inline int32_t open(const char* filename, uint32_t flags) {return openat(AT_FDCWD, filename, flags, 0);}
+
 uint32_t fork();
 
 // Provide memset for clang