Fix pcprofiledump cross-endian condition (bug 22086).

debug/pcprofiledump.c contains code that tries to handle other-endian
data.  This uses a condition "(word & 0xfffffff0) == bswap_32
(0xdeb00000)".  This condition is always false (the LHS always has the
low four bits zero, the RHS doesn't); a correct comparison would use
0x0fffffff.  This results in -Werror=tautological-compare build
failures with the tile version of bits/byteswap.h and mainline GCC.

https://sourceware.org/ml/libc-testresults/2017-q3/msg00400.html

pcprofiledump.c: In function 'main':
pcprofiledump.c:118:39: error: bitwise comparison always evaluates to false
[-Werror=tautological-compare]
   int must_swap = (word & 0xfffffff0) == bswap_32 (0xdeb00000);
                                       ^~

This patch fixes the condition.  Tested for x86_64, and with
build-many-glibcs.py that it fixes the build for tilegx-linux-gnu.
(Note that I have not tested the actual pcprofiledump functionality,
native or cross endian, which lacks any testsuite coverage.)

	[BZ #22086]
	* debug/pcprofiledump.c (main): Use byte-swapped mask when
	comparing word with byte-swapped constant.

diff --git a/ChangeLog b/ChangeLog
index 00255b7..d148e74 100644 (file)
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+2017-09-05  Joseph Myers  <joseph@codesourcery.com>
+
+       [BZ #22086]
+       * debug/pcprofiledump.c (main): Use byte-swapped mask when
+       comparing word with byte-swapped constant.
+
 2017-09-05  Chris Leonard <cjlhomeaddress@gmail.com>
 
        [BZ #20498]

diff --git a/debug/pcprofiledump.c b/debug/pcprofiledump.c
index a32cdef..6a9641e 100644 (file)
--- a/debug/pcprofiledump.c
+++ b/debug/pcprofiledump.c
@@ -115,7 +115,7 @@ main (int argc, char *argv[])
     error (EXIT_FAILURE, errno, _("cannot read header"));
 
   /* Check whether we have to swap the byte order.  */
-  int must_swap = (word & 0xfffffff0) == bswap_32 (0xdeb00000);
+  int must_swap = (word & 0x0fffffff) == bswap_32 (0xdeb00000);
   if (must_swap)
     word = bswap_32 (word);