[PING][PATCH] Ignore alignment by option

[Marat Zakirov <m dot zakirov at samsung dot com>]

On 11/19/2014 06:01 PM, Marat Zakirov wrote:
> Hi all!
>
> Here is the patch which forces ASan to ignore alignment of memory 
> access. It increases ASan overhead but it's still useful because some 
> programs like linux kernel often cheat with alignment which may cause 
> false negatives.
>
> --Marat

gcc/ChangeLog:

2014-11-14  Marat Zakirov  <m.zakirov@samsung.com>

	* asan.c (asan_expand_check_ifn): Ignore alignment by option.  
	* doc/invoke.texi: Document.  
	* params.def (asan-alignment-optimize): New.  
	* params.h: Likewise.  

gcc/testsuite/ChangeLog:

2014-11-14  Marat Zakirov  <m.zakirov@samsung.com>

	* c-c++-common/asan/red-align-3.c: New test.  


diff --git a/gcc/asan.c b/gcc/asan.c
index 79dede7..4f86088 100644
--- a/gcc/asan.c
+++ b/gcc/asan.c
@@ -2518,6 +2518,12 @@ asan_expand_check_ifn (gimple_stmt_iterator *iter, bool use_calls)
 
   HOST_WIDE_INT size_in_bytes
     = is_scalar_access && tree_fits_shwi_p (len) ? tree_to_shwi (len) : -1;
+  
+  if (!ASAN_ALIGNMENT_OPTIMIZE && size_in_bytes > 1)
+    {
+      size_in_bytes = -1;
+      align = 1;
+    }
 
   if (use_calls)
     {
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index 13270bc..8f43c06 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -10580,6 +10580,12 @@ is greater or equal to this number, use callbacks instead of inline checks.
 E.g. to disable inline code use
 @option{--param asan-instrumentation-with-call-threshold=0}.
 
+@item asan-alignment-optimize
+Enable asan optimization for aligned accesses.
+It is enabled by default when using @option{-fsanitize=address} option.
+To disable optimization for aligned accesses use 
+@option{--param asan-alignment-optimize=0}.
+
 @item chkp-max-ctor-size
 Static constructors generated by Pointer Bounds Checker may become very
 large and significantly increase compile time at optimization level
diff --git a/gcc/params.def b/gcc/params.def
index d2d2add..fbccf46 100644
--- a/gcc/params.def
+++ b/gcc/params.def
@@ -1114,6 +1114,11 @@ DEFPARAM (PARAM_ASAN_INSTRUMENTATION_WITH_CALL_THRESHOLD,
          "in function becomes greater or equal to this number",
          7000, 0, INT_MAX)
 
+DEFPARAM (PARAM_ASAN_ALIGNMENT_OPTIMIZE,
+         "asan-alignment-optimize",
+         "Enable asan optimization for aligned access",
+         1, 0, 1)
+
 DEFPARAM (PARAM_UNINIT_CONTROL_DEP_ATTEMPTS,
 	  "uninit-control-dep-attempts",
 	  "Maximum number of nested calls to search for control dependencies "
diff --git a/gcc/params.h b/gcc/params.h
index 4779e17..e2973d4 100644
--- a/gcc/params.h
+++ b/gcc/params.h
@@ -238,5 +238,7 @@ extern void init_param_values (int *params);
   PARAM_VALUE (PARAM_ASAN_USE_AFTER_RETURN)
 #define ASAN_INSTRUMENTATION_WITH_CALL_THRESHOLD \
   PARAM_VALUE (PARAM_ASAN_INSTRUMENTATION_WITH_CALL_THRESHOLD)
+#define ASAN_ALIGNMENT_OPTIMIZE \
+  PARAM_VALUE (PARAM_ASAN_ALIGNMENT_OPTIMIZE)
 
 #endif /* ! GCC_PARAMS_H */
diff --git a/gcc/testsuite/c-c++-common/asan/ignore_align.c b/gcc/testsuite/c-c++-common/asan/ignore_align.c
new file mode 100644
index 0000000..989958b
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/asan/ignore_align.c
@@ -0,0 +1,34 @@
+/* { dg-options "-fdump-tree-sanopt --param asan-alignment-optimize=0" } */
+/* { dg-do compile } */
+/* { dg-skip-if "" { *-*-* } { "-flto" } { "" } } */
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+void *memset (void *, int, __SIZE_TYPE__);
+#ifdef __cplusplus
+}
+#endif
+
+struct dummy {
+  int a;
+  int b;
+  int c;
+  int d;
+};
+
+volatile struct dummy * new_p;
+volatile struct dummy * old_p; 
+
+void foo(void)
+{
+  *(volatile char *)(0x12);
+  *(volatile short int *)(0x12);
+  *(volatile unsigned int *)(0x12);
+  *(volatile unsigned long long *)(0x12);
+  *new_p = *old_p;
+}
+
+/* { dg-final { scan-tree-dump-times ">> 3" 11 "sanopt" } } */
+/* { dg-final { scan-tree-dump-times "& 7" 11 "sanopt" } } */
+/* { dg-final { cleanup-tree-dump "sanopt" } } */