Fix x86_64 memchr for large input sizes

Current optimized memchr for x86_64 does for input arguments pointers
module 64 in range of [49,63] if there is no searchr char in the rest
of 64-byte block a pointer addition which might overflow:

* sysdeps/x86_64/memchr.S

    77          .p2align 4
    78  L(unaligned_no_match):
    79          add     %rcx, %rdx

Add (uintptr_t)s % 16 to n in %rdx.

    80          sub     $16, %rdx
    81          jbe     L(return_null)

This patch fixes by adding a saturated math that sets a maximum pointer
value if it overflows (UINTPTR_MAX).

Checked on x86_64-linux-gnu and powerpc64-linux-gnu.

	[BZ# 19387]
	* sysdeps/x86_64/memchr.S (memchr): Avoid overflow in pointer
	addition.
	* string/test-memchr.c (do_test): Remove alignment limitation.
	(test_main): Add test that trigger BZ# 19387.

1 files changed, 4 insertions, 5 deletions

diff --git a/string/test-memchr.c b/string/test-memchr.c
index 0690cb4..10d696a 100644
--- a/string/test-memchr.c
+++ b/string/test-memchr.c
@@ -76,7 +76,6 @@ do_test (size_t align, size_t pos, size_t len, size_t n, int seek_char)
   size_t i;
   CHAR *result;
 
-  align &= 7;
   if ((align + len) * sizeof (CHAR) >= page_size)
     return;
 
@@ -194,12 +193,12 @@ test_main (void)
       do_test (i, 64, 256, SIZE_MAX, 0);
     }
 
-  for (i = 1; i < 16; ++i)
+  for (i = 1; i < 64; ++i)
     {
-      for (j = 1; j < 16; j++)
+      for (j = 1; j < 64; j++)
         {
-	  do_test (0, 16 - j, 16, SIZE_MAX, 23);
-	  do_test (i, 16 - j, 16, SIZE_MAX, 23);
+	  do_test (0, 64 - j, 64, SIZE_MAX, 23);
+	  do_test (i, 64 - j, 64, SIZE_MAX, 23);
         }
     }