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

From: Cyril Bur <[email-masked]>
Date: Fri, 10 Feb 2017 16:31:15 +1100

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 <[email-masked]>
Signed-off-by: Cyril Bur <[email-masked]>
---
 arch/powerpc/Makefile | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/arch/powerpc/Makefile b/arch/powerpc/Makefile
index 31286fa7873c..a4b886694391 100644
--- a/arch/powerpc/Makefile
+++ b/arch/powerpc/Makefile
@@ -414,6 +414,15 @@ checkbin:
 		echo -n '*** Please use a different binutils version.' ; \
 		false ; \
 	fi
+	@if 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 commandline options (at least).' ; \
+		echo '*** Please use a different GCC version.' ; \
+		false ; \
+	fi
+

 CLEAN_FILES += $(TOUT)
-- 
2.11.1