* [2.28 COMMITTED] support: Do not require overflow builtin in support/blob_repeat.c
@ 2018-01-01 0:00 Florian Weimer
0 siblings, 0 replies; only message in thread
From: Florian Weimer @ 2018-01-01 0:00 UTC (permalink / raw)
To: libc-stable
It is only available in GCC 5 and later.
Tested-by: Romain Naour <romain.naour@gmail.com>
(cherry picked from commit 0c1719e65b2a5a80331d4f635612799f853b0479)
2018-12-15 Florian Weimer <fweimer@redhat.com>
* support/blob_repeat.c (check_mul_overflow_size_t): New function.
(minimum_stride_size): Use it.
(support_blob_repeat_allocate): Likewise.
diff --git a/support/blob_repeat.c b/support/blob_repeat.c
index 16c1e448b9..718846d81d 100644
--- a/support/blob_repeat.c
+++ b/support/blob_repeat.c
@@ -34,6 +34,26 @@
optimization because mappings carry a lot of overhead. */
static const size_t maximum_small_size = 4 * 1024 * 1024;
+/* Set *RESULT to LEFT * RIGHT. Return true if the multiplication
+ overflowed. See <malloc/malloc-internal.h>. */
+static inline bool
+check_mul_overflow_size_t (size_t left, size_t right, size_t *result)
+{
+#if __GNUC__ >= 5
+ return __builtin_mul_overflow (left, right, result);
+#else
+ /* size_t is unsigned so the behavior on overflow is defined. */
+ *result = left * right;
+ size_t half_size_t = ((size_t) 1) << (8 * sizeof (size_t) / 2);
+ if (__glibc_unlikely ((left | right) >= half_size_t))
+ {
+ if (__glibc_unlikely (right != 0 && *result / right != left))
+ return true;
+ }
+ return false;
+#endif
+}
+
/* Internal helper for fill. */
static void
fill0 (char *target, const char *element, size_t element_size,
@@ -118,8 +138,8 @@ minimum_stride_size (size_t page_size, size_t element_size)
common multiple, it appears only once. Therefore, shift one
factor. */
size_t multiple;
- if (__builtin_mul_overflow (page_size >> common_zeros, element_size,
- &multiple))
+ if (check_mul_overflow_size_t (page_size >> common_zeros, element_size,
+ &multiple))
return 0;
return multiple;
}
@@ -255,7 +275,7 @@ support_blob_repeat_allocate (const void *element, size_t element_size,
size_t count)
{
size_t total_size;
- if (__builtin_mul_overflow (element_size, count, &total_size))
+ if (check_mul_overflow_size_t (element_size, count, &total_size))
{
errno = EOVERFLOW;
return (struct support_blob_repeat) { 0 };
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2018-01-01 0:00 [2.28 COMMITTED] support: Do not require overflow builtin in support/blob_repeat.c Florian Weimer
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