[PATCH] Fix typing of the bit twiddling done in _dl_setup_stack_chk_guard.

[David Miller]

I noticed a warning that triggers on big-endian 64-bit platforms.

Basically:

	(0xff << (8 * (sizeof (ret) - 1)))

Doesn't work because 0xff is an "unsigned int" (which is 32-bit) and
we're shifting up into the topmost byte of "ret" based upon it's size
which is "sizeof(uintptr_t)" which is 64-bit.

I used a cast to get the typing right, and I added a cast to the
little-endian case for consistency, even though it isn't strictly
necessary.

Just out of curiosity I took a look at how GCC handles this undefined
situation using this code snippet:

--------------------
unsigned long bar(unsigned long x)
{
	return x & (0xff << (8 * (sizeof(unsigned long) - 1)));
}
--------------------

For 64-bit sparc it essentially truncated the shift to 24-bits and
generated this:

	mov	-1, %g1
	sllx	%g1, 24, %g1
	and	%o0, %g1, %o0

And on x86-64 gcc emits "xorl %eax, %eax" :-)

Committed to master.

	* sysdeps/unix/sysv/linux/dl-osinfo.h (_dl_setup_stack_chk_guard):
	Fix masking out of the most significant byte of random value used.
---
 ChangeLog                           |    3 +++
 sysdeps/unix/sysv/linux/dl-osinfo.h |    4 ++--
 2 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index 85993dc..29b7c67 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,8 @@
 2012-03-11  David S. Miller  <davem@davemloft.net>
 
+	* sysdeps/unix/sysv/linux/dl-osinfo.h (_dl_setup_stack_chk_guard):
+	Fix masking out of the most significant byte of random value used.
+
 	* sysdeps/sparc/fpu/libm-test-ulps: Update.
 
 2012-03-10  Andreas Schwab  <schwab@linux-m68k.org>
diff --git a/sysdeps/unix/sysv/linux/dl-osinfo.h b/sysdeps/unix/sysv/linux/dl-osinfo.h
index 780b20a..1ff8a2f 100644
--- a/sysdeps/unix/sysv/linux/dl-osinfo.h
+++ b/sysdeps/unix/sysv/linux/dl-osinfo.h
@@ -95,9 +95,9 @@ _dl_setup_stack_chk_guard (void *dl_random)
 	 directly and not use the kernel-provided data to seed a PRNG.  */
       memcpy (ret.bytes, dl_random, sizeof (ret));
 #if BYTE_ORDER == LITTLE_ENDIAN
-      ret.num &= ~0xff;
+      ret.num &= ~(uintptr_t)0xff;
 #elif BYTE_ORDER == BIG_ENDIAN
-      ret.num &= ~(0xff << (8 * (sizeof (ret) - 1)));
+      ret.num &= ~((uintptr_t)0xff << (8 * (sizeof (ret) - 1)));
 #else
 # error "BYTE_ORDER unknown"
 #endif
-- 
1.7.6.401.g6a319