linux-kernel - [tip:perf/core] recordmcount: Fix handling of elf64 big-endian objects.

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Date:	Sun, 8 Jan 2012 03:51:09 -0800
From:	tip-bot for David Daney <david.daney@...ium.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, hpa@...or.com, mingo@...hat.com,
	rostedt@...dmis.org, david.daney@...ium.com, tglx@...utronix.de
Subject: [tip:perf/core] recordmcount:
  Fix handling of elf64 big-endian objects.

Commit-ID:  2e885057b7f75035f0b85e02f737891482815a81
Gitweb:     http://git.kernel.org/tip/2e885057b7f75035f0b85e02f737891482815a81
Author:     David Daney <david.daney@...ium.com>
AuthorDate: Mon, 19 Dec 2011 17:42:42 -0800
Committer:  Steven Rostedt <rostedt@...dmis.org>
CommitDate: Fri, 6 Jan 2012 17:06:42 -0500

recordmcount: Fix handling of elf64 big-endian objects.

In ELF64, the sh_flags field is 64-bits wide.  recordmcount was
erroneously treating it as a 32-bit wide field.  For little endian
objects this works because the flags of interest (SHF_EXECINSTR)
reside in the lower 32 bits of the word, and you get the same result
with either a 32-bit or 64-bit read.  Big endian objects on the
other hand do not work at all with this error.

The fix:  Correctly treat sh_flags as 64-bits wide in elf64 objects.

The symptom I observed was that my
__start_mcount_loc..__stop_mcount_loc was empty even though ftrace
function tracing was enabled.

Link: http://lkml.kernel.org/r/1324345362-12230-1-git-send-email-ddaney.cavm@gmail.com

Cc: stable@...nel.org # 3.0+
Signed-off-by: David Daney <david.daney@...ium.com>
Signed-off-by: Steven Rostedt <rostedt@...dmis.org>
---
 scripts/recordmcount.h |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/scripts/recordmcount.h b/scripts/recordmcount.h
index f40a6af6..54e35c1 100644
--- a/scripts/recordmcount.h
+++ b/scripts/recordmcount.h
@@ -462,7 +462,7 @@ __has_rel_mcount(Elf_Shdr const *const relhdr,  /* is SHT_REL or SHT_RELA */
 		succeed_file();
 	}
 	if (w(txthdr->sh_type) != SHT_PROGBITS ||
-	    !(w(txthdr->sh_flags) & SHF_EXECINSTR))
+	    !(_w(txthdr->sh_flags) & SHF_EXECINSTR))
 		return NULL;
 	return txtname;
 }
--
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