From: Cyril Bur <cyrilbur@gmail.com>

To: linuxppc-dev@lists.ozlabs.org

Subject: [PATCH v2] powerpc: Blacklist GCC 5.4 6.1 and 6.2

Date: Mon, 13 Feb 2017 14:35:36 +1100

Message-Id: <20170213033536.8908-1-cyrilbur@gmail.com>

References: boo#1028895

Patch-mainline: submitted http://patchwork.ozlabs.org/patch/727105/

A bug in the -02 optimisation of GCC 5.4 6.1 and 6.2 causes

setup_command_line() to not pass the correct first argument to strcpy

and therefore not actually copy the command_line.

A workaround patch was proposed: http://patchwork.ozlabs.org/patch/673130/

some discussion ensued.

A GCC bug was raised: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71709

The bug has been fixed in 7.0 and backported to GCC 5 and GCC 6.

At the time of writing GCC 5.4 is the most recent and is affected. GCC

6.3 contains the backported fix, has been tested and appears safe to

use.

Heavy-lifting-by: Akshay Adiga <akshay.adiga@linux.vnet.ibm.com>

Signed-off-by: Cyril Bur <cyrilbur@gmail.com>

Acked-by: Michal Suchanek <msuchanek@suse.de>

---

v2: Added check to only blacklist compilers on little-endian

 arch/powerpc/Makefile |    9 +++++++++

 1 file changed, 9 insertions(+)

--- a/arch/powerpc/Makefile

+++ b/arch/powerpc/Makefile

@@ -449,3 +449,12 @@ checkbin:

 		echo -n '*** Please use a different binutils version.' ; \

 		false ; \

 	fi

+	@if test "x${CONFIG_CPU_LITTLE_ENDIAN}" = "xy" \

+		&& { test "$(cc-version)" = "0504" \

+		|| test "$(cc-version)" = "0601" \

+		|| test "$(cc-version)" = "0602" ; } ; then \

+		echo -n '*** GCC-5.4 6.1 6.2 have a bad -O2 optimisation ' ; \

+		echo 'which will cause lost command_line options (at least).' ; \

+		echo '*** Please use a different GCC version.' ; \

+		false ; \

+	fi