linux-kernel - [RFC PATCH 0/4] Nop out the preceding mflr with -mprofile-kernel

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Message-Id: <cover.1558115654.git.naveen.n.rao@linux.vnet.ibm.com>
Date:   Sat, 18 May 2019 00:32:44 +0530
From:   "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>
To:     Steven Rostedt <rostedt@...dmis.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Nicholas Piggin <npiggin@...il.com>
Cc:     <linuxppc-dev@...ts.ozlabs.org>, <linux-kernel@...r.kernel.org>
Subject: [RFC PATCH 0/4] Nop out the preceding mflr with -mprofile-kernel

On powerpc64, -mprofile-kernel results in two instructions being 
emitted: 'mflr r0' and 'bl _mcount'. So far, we were only nop'ing out 
the branch to _mcount(). This series implements an approach to also nop 
out the preceding mflr.

Patches 1-3 are generic changes. Patch 2 is a fix for x86, but has not 
been tested. Patch 4 implements the changes for powerpc64.


- Naveen

Naveen N. Rao (4):
  ftrace: Expose flags used for ftrace_replace_code()
  x86/ftrace: Fix use of flags in ftrace_replace_code()
  ftrace: Expose __ftrace_replace_code()
  powerpc/ftrace: Additionally nop out the preceding mflr with
    -mprofile-kernel

 arch/powerpc/kernel/trace/ftrace.c | 188 +++++++++++++++++++++++++----
 arch/x86/kernel/ftrace.c           |   3 +-
 include/linux/ftrace.h             |   6 +
 kernel/trace/ftrace.c              |  13 +-
 4 files changed, 178 insertions(+), 32 deletions(-)

-- 
2.21.0