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From: Steven Rostedt on 22 Jul 2010 16:30
From: David Daney <ddaney(a)caviumnetworks.com>

I found this issue in a locally patched 2.6.32.x, current kernels have
moved the offending code to an __init function which is skipped by
recordmcount.pl, so the bug is not currently being exercised.
However, I think the patch is still a good idea, to avoid future
problems if _mcount were to ever have its address taken in normal
code.

This is what I originally saw:

Although arch/mips/kernel/ftrace.c is built without -pg, and thus
contains no calls to _mcount, it does use the address of _mcount
in ftrace_make_nop(). This was causing relocations to be emitted
for _mcount which recordmcount.pl erronously took to be _mcount
call sites. The result was that the text of ftrace_make_nop()
would be patched with garbage leading to a system crash.

In non-module code, all _mcount call sites will have R_MIPS_26
relocations, so we restrict $mcount_regex to only match on these.

Acked-by: Ralf Baechle <ralf(a)linux-mips.org>
Acked-by: Wu Zhangjin <wuzhangjin(a)gmail.com>
Signed-off-by: David Daney <ddaney(a)caviumnetworks.com>
LKML-Reference: <1278712325-12050-1-git-send-email-ddaney(a)caviumnetworks.com>
Cc: Li Hong <lihong.hi(a)gmail.com>
Cc: Ingo Molnar <mingo(a)elte.hu>
Cc: Matt Fleming <matt(a)console-pimps.org>
Signed-off-by: Steven Rostedt <rostedt(a)goodmis.org>
---
scripts/recordmcount.pl | 2 +-
1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/scripts/recordmcount.pl b/scripts/recordmcount.pl
index f3c9c0a..0171060 100755
--- a/scripts/recordmcount.pl
+++ b/scripts/recordmcount.pl
@@ -326,7 +326,7 @@ if ($arch eq "x86_64") {
# 14: R_MIPS_NONE *ABS*
# 18: 00020021 nop
if ($is_module eq "0") {
- $mcount_regex = "^\\s*([0-9a-fA-F]+):.*\\s_mcount\$";
+ $mcount_regex = "^\\s*([0-9a-fA-F]+): R_MIPS_26\\s+_mcount\$";
} else {
$mcount_regex = "^\\s*([0-9a-fA-F]+): R_MIPS_HI16\\s+_mcount\$";
}
--
1.7.1


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