Subzero: removed loops from ASan access checking

runtime/szrt_asan.c

 //===- subzero/runtime/szrt_asan.c - AddressSanitizer Runtime -----*- C -*-===//
 //
 //                        The Subzero Code Generator
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 ///
 /// \file
@@ skipping 40 matching lines @@
   do {                                                                         \
     printf(args);                                                              \
   } while (false);
 #else // !DEBUG
 #define DUMP(args...)
 #endif // DEBUG
 
 static char *shadow_offset = NULL;
 
 static void __asan_error(char *, int);
-static void __asan_check(char *, int, bool);
+static void __asan_check(char *, int);
 static void __asan_get_redzones(char *, char **, char **);
 
 void __asan_init(int, void **, int *);
 void __asan_check_load(char *, int);
 void __asan_check_store(char *, int);
 void *__asan_malloc(size_t);
 void *__asan_calloc(size_t, size_t);
 void *__asan_realloc(char *, size_t);
 void __asan_free(char *);
 void __asan_poison(char *, int);
 void __asan_unpoison(char *, int);
 
 static void __asan_error(char *ptr, int size) {
   fprintf(stderr, "Illegal access of %d bytes at %p\n", size, ptr);
   abort();
 }
 
 // check only the first byte of each word unless strict
-static void __asan_check(char *ptr, int size, bool strict) {
-  assert(strict || (uintptr_t)ptr % WORD_SIZE == 0);
-  DUMP("%s check %d bytes at %p\n", (strict) ? "strict" : "loose", size, ptr);
-  char *end = ptr + size;
-  int step = (strict) ? 1 : WORD_SIZE;
-  for (char *cur = ptr; cur < end; cur += step) {
-    char shadow = *(char *)MEM2SHADOW(cur);
-    DUMP("checking %p against %p with shadow %d\n", cur, MEM2SHADOW(cur),
-         shadow);
-    if (shadow != 0 && (shadow < 0 || SHADOW_OFFSET(cur) >= shadow)) {
+static void __asan_check(char *ptr, int size) {
+  assert(size == 1 || size == 2 || size == 4 || size == 8);
+  char *shadow_addr = (char *)MEM2SHADOW(ptr);
+  DUMP("check %d bytes at %p: %p + %d (%d)\n", size, ptr, shadow_addr,
+       (uintptr_t)ptr % SHADOW_SCALE, *shadow_addr);
+  if (size == SHADOW_SCALE) {
+    if (*shadow_addr != 0)
       __asan_error(ptr, size);
-    }
+    return;
   }
+  if (*shadow_addr != 0 && (char)SHADOW_OFFSET(ptr) + size > *shadow_addr)
+    __asan_error(ptr, size);
 }
 
 static void __asan_get_redzones(char *ptr, char **left, char **right) {
   char *rz_left = ptr - RZ_SIZE;
   char *rz_right = *(char **)rz_left;
   if (left != NULL)
     *left = rz_left;
   if (right != NULL)
     *right = rz_right;
 }
 
 void __asan_check_load(char *ptr, int size) {
   // aligned single word accesses may be widened single byte accesses, but for
   // all else use strict check
-  bool strict = !((uintptr_t)ptr % WORD_SIZE == 0 && size == WORD_SIZE);
-  __asan_check(ptr, size, strict);
+  if (size == WORD_SIZE && (uintptr_t)ptr % WORD_SIZE == 0)
+    size = 1;
+  __asan_check(ptr, size);
 }
 
 void __asan_check_store(char *ptr, int size) {
   // stores may never be partially out of bounds so use strict check
   bool strict = true;
-  __asan_check(ptr, size, strict);
+  __asan_check(ptr, size);
 }
 
 void __asan_init(int n_rzs, void **rzs, int *rz_sizes) {
   // ensure the redzones are large enough to hold metadata
   assert(RZ_SIZE >= sizeof(void *) && RZ_SIZE >= sizeof(size_t));
   assert(shadow_offset == NULL);
   size_t length = (IS_32_BIT) ? SHADOW_LENGTH_32 : SHADOW_LENGTH_64;
   int prot = PROT_READ | PROT_WRITE;
   int flags = MAP_PRIVATE | MAP_ANONYMOUS;
   int fd = -1;
@@ skipping 101 matching lines @@
   assert(size < 2 * RZ_SIZE);
   DUMP("unpoison %d bytes at %p: %p - %p\n", size, ptr, MEM2SHADOW(ptr),
        MEM2SHADOW(end));
   *(char *)MEM2SHADOW(ptr) = 0;
   ptr += SHADOW_OFFSET(size);
   assert(IS_SHADOW_ALIGNED(ptr));
   for (; ptr != end; ptr += SHADOW_SCALE) {
     *(char *)MEM2SHADOW(ptr) = 0;
   }
 }