linux-kernel - [PATCH RFC 1/2] Makefile: Never use -fno-omit-frame-pointer

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Date:	Wed, 17 Jun 2009 00:16:30 +0400
From:	Anton Vorontsov <avorontsov@...mvista.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Steven Rostedt <srostedt@...hat.com>,
	Segher Boessenkool <segher@...nel.crashing.org>,
	Sam Ravnborg <sam@...nborg.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	linuxppc-dev@...abs.org, linux-kernel@...r.kernel.org
Subject: [PATCH RFC 1/2] Makefile: Never use -fno-omit-frame-pointer

According to Segher Boessenkool and GCC manual, -fomit-frame-pointer
is only the default when optimising on archs/ABIs where it doesn't
hinder debugging and -pg. So, we do not get it by default on x86,
not at any optimisation level.

On the other hand, *using* -fno-omit-frame-pointer causes gcc to
produce buggy code on PowerPC targets.

If Segher and GCC manual are right, this patch should be a no-op
for all arches except PowerPC, where the patch fixes gcc issues.

Signed-off-by: Anton Vorontsov <avorontsov@...mvista.com>
---

See this thread for more discussion:
http://osdir.com/ml/linux-kernel/2009-05/msg01754.html

p.s.
Obviously, I didn't test this patch on anything else but PPC32. ;-)

Segher, do you know if all GCC versions that we support for
building Linux are behaving the way that GCC manual describe?

Thanks,

 Makefile |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/Makefile b/Makefile
index ea63667..70ad1ff 100644
--- a/Makefile
+++ b/Makefile
@@ -535,7 +535,7 @@ KBUILD_CFLAGS += $(call cc-option, -fno-stack-protector)
 endif

 ifdef CONFIG_FRAME_POINTER
-KBUILD_CFLAGS	+= -fno-omit-frame-pointer -fno-optimize-sibling-calls
+KBUILD_CFLAGS	+= -fno-optimize-sibling-calls
 else
 KBUILD_CFLAGS	+= -fomit-frame-pointer
 endif
-- 
1.6.3.1

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