Add gcc_assert about stack alignment (PR sanitizer/82517).

2018-01-09  Martin Liska  <mliska@suse.cz>

	PR sanitizer/82517
	* asan.c (shadow_mem_size): Add gcc_assert.

From-SVN: r256378

gcc/ChangeLog

+2018-01-09  Martin Liska  <mliska@suse.cz>
+
+	PR sanitizer/82517
+	* asan.c (shadow_mem_size): Add gcc_assert.
+
 2018-01-09  Georg-Johann Lay  <avr@gjlay.de>
 
 	Don't save registers in main().

gcc/asan.c

@@ -1228,6 +1228,11 @@ asan_function_start (void)
 static unsigned HOST_WIDE_INT
 shadow_mem_size (unsigned HOST_WIDE_INT size)
 {
+  /* It must be possible to align stack variables to granularity
+     of shadow memory.  */
+  gcc_assert (BITS_PER_UNIT
+	      * ASAN_SHADOW_GRANULARITY <= MAX_SUPPORTED_STACK_ALIGNMENT);
+
   return ROUND_UP (size, ASAN_SHADOW_GRANULARITY) / ASAN_SHADOW_GRANULARITY;
 }