linux-kernel - [PATCH 10/14] perf jit: memset() variable 'st' using the correct size

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Date:	Tue, 19 Apr 2016 12:50:37 -0300
From:	Arnaldo Carvalho de Melo <acme@...nel.org>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	linux-kernel@...r.kernel.org,
	Colin Ian King <colin.king@...onical.com>,
	Adrian Hunter <adrian.hunter@...el.com>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Stephane Eranian <eranian@...gle.com>,
	Arnaldo Carvalho de Melo <acme@...hat.com>
Subject: [PATCH 10/14] perf jit: memset() variable 'st' using the correct size

From: Colin Ian King <colin.king@...onical.com>

The current code is memsetting the 'struct stat' variable 'st' with the size of
'stat' (which turns out to be 1 byte) rather than the size of variable 'sz'.

Committer notes:

sizeof(function) isn't valid, the result depends on the compiler used, with
gcc, enabling pedantic warnings we get:

  $ cat sizeof_function.c
  #include <sys/types.h>
  #include <sys/stat.h>
  #include <unistd.h>
  #include <stdio.h>

  int main(void)
  {
	  printf("sizeof(stat)=%zd, stat=%p\n", sizeof(stat), stat);
	  return 0;
  }
  $ readelf -sW sizeof_function | grep -w stat
      49: 0000000000400630    16 FUNC    WEAK   HIDDEN    13 stat
  $ cc -pedantic sizeof_function.c   -o sizeof_function
  sizeof_function.c: In function ‘main’:
  sizeof_function.c:8:46: warning: invalid application of ‘sizeof’ to a function type [-Wpointer-arith]
    printf("sizeof(stat)=%zd, stat=%p\n", sizeof(stat), stat);
                                              ^
  $ ./sizeof_function
  sizeof(stat)=1, stat=0x400630
  $

  Standard C, section 6.5.3.4:

  "The sizeof operator shall not be applied to an expression that has function
   type or an incomplete type, to the parenthesized name of such a type,
   or to an expression that designates a bit-field member."

  http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1256.pdf

Signed-off-by: Colin Ian King <colin.king@...onical.com>
Tested-by: Arnaldo Carvalho de Melo <acme@...hat.com>
Cc: Adrian Hunter <adrian.hunter@...el.com>
Cc: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Stephane Eranian <eranian@...gle.com>
Fixes: 9b07e27f88b9 ("perf inject: Add jitdump mmap injection support")
Link: http://lkml.kernel.org/r/1461020838-9260-1-git-send-email-colin.king@canonical.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@...hat.com>
---
 tools/perf/util/jitdump.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/tools/perf/util/jitdump.c b/tools/perf/util/jitdump.c
index 52fcef3074fe..86afe9618bb0 100644
--- a/tools/perf/util/jitdump.c
+++ b/tools/perf/util/jitdump.c
@@ -412,7 +412,7 @@ static int jit_repipe_code_load(struct jit_buf_desc *jd, union jr_entry *jr)
 		return -1;
 	}
 	if (stat(filename, &st))
-		memset(&st, 0, sizeof(stat));
+		memset(&st, 0, sizeof(st));
 
 	event->mmap2.header.type = PERF_RECORD_MMAP2;
 	event->mmap2.header.misc = PERF_RECORD_MISC_USER;
@@ -500,7 +500,7 @@ static int jit_repipe_code_move(struct jit_buf_desc *jd, union jr_entry *jr)
 	size++; /* for \0 */
 
 	if (stat(filename, &st))
-		memset(&st, 0, sizeof(stat));
+		memset(&st, 0, sizeof(st));
 
 	size = PERF_ALIGN(size, sizeof(u64));
 
-- 
2.5.5