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