linux-kernel - [PATCH 4/5] gcov: disable tree-loop-im to reduce stack usage

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Message-Id: <1455293187-179811-5-git-send-email-arnd@arndb.de>
Date:	Fri, 12 Feb 2016 17:06:21 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	Michal Marek <mmarek@...e.com>
Cc:	linux-arm-kernel@...ts.infradead.org,
	Peter Oberparleiter <oberpar@...ux.vnet.ibm.com>,
	linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org,
	Arnd Bergmann <arnd@...db.de>
Subject: [PATCH 4/5] gcov: disable tree-loop-im to reduce stack usage

Enabling CONFIG_GCOV_PROFILE_ALL produces us a lot of warnings like

lib/lz4/lz4hc_compress.c: In function 'lz4_compresshcctx':
lib/lz4/lz4hc_compress.c:514:1: warning: the frame size of 1504 bytes is larger than 1024 bytes [-Wframe-larger-than=]

After some investigation, I found that this behavior started with gcc-4.9,
and opened https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69702.
A suggested workaround for it is to use the -fno-tree-loop-im
flag that turns off one of the optimization stages in gcc, so the
code runs a little slower but does not use excessive amounts
of stack.

We could make this conditional on the gcc version, but I could not
find an easy way to do this in Kbuild and the benefit would be
fairly small, given that most of the gcc version in production are
affected now.

Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
 Makefile | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Makefile b/Makefile
index 352f55ccc54e..6bb89728a9d1 100644
--- a/Makefile
+++ b/Makefile
@@ -364,7 +364,7 @@ AFLAGS_MODULE   =
 LDFLAGS_MODULE  =
 CFLAGS_KERNEL	=
 AFLAGS_KERNEL	=
-CFLAGS_GCOV	= -fprofile-arcs -ftest-coverage
+CFLAGS_GCOV	= -fprofile-arcs -ftest-coverage -fno-tree-loop-im
 CFLAGS_KCOV	= -fsanitize-coverage=trace-pc

-- 
2.7.0