linux-kernel - [PATCH] Only add -fno-var-tracking-assignments workaround for old GCC versions.

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Message-Id: <20201014110132.2680-1-mark@klomp.org>
Date:   Wed, 14 Oct 2020 13:01:32 +0200
From:   Mark Wielaard <mark@...mp.org>
To:     linux-kernel@...r.kernel.org,
        Masahiro Yamada <masahiroy@...nel.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        linux-kbuild@...r.kernel.org
Cc:     Ian Rogers <irogers@...gle.com>, Mark Wielaard <mark@...mp.org>,
        linux-toolchains@...r.kernel.org, Andi Kleen <andi@...stfloor.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Segher Boessenkool <segher@...nel.crashing.org>,
        Florian Weimer <fw@...eb.enyo.de>
Subject: [PATCH] Only add -fno-var-tracking-assignments workaround for old GCC versions.

Some old GCC versions between 4.5.0 and 4.9.1 might miscompile code
with -fvar-tracking-assingments (which is enabled by default with -g -O2).
commit 2062afb4f added -fno-var-tracking-assignments unconditionally to
work around this. But newer versions of GCC no longer have this bug, so
only add it for versions of GCC before 5.0.

Signed-off-by: Mark Wielaard <mark@...mp.org>
Acked-by: Ian Rogers <irogers@...gle.com>
Cc: linux-toolchains@...r.kernel.org
Cc: Andi Kleen <andi@...stfloor.org>
Cc: Nick Desaulniers <ndesaulniers@...gle.com>
Cc: Segher Boessenkool <segher@...nel.crashing.org>
Cc: Florian Weimer <fw@...eb.enyo.de>
---
 Makefile | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/Makefile b/Makefile
index 51540b291738..8477fee5f309 100644
--- a/Makefile
+++ b/Makefile
@@ -813,7 +813,9 @@ KBUILD_CFLAGS	+= -ftrivial-auto-var-init=zero
 KBUILD_CFLAGS	+= -enable-trivial-auto-var-init-zero-knowing-it-will-be-removed-from-clang
 endif
 
-DEBUG_CFLAGS	:= $(call cc-option, -fno-var-tracking-assignments)
+# Workaround https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61801
+# for old versions of GCC.
+DEBUG_CFLAGS	:= $(call cc-ifversion, -lt, 0500, $(call cc-option, -fno-var-tracking-assignments))
 
 ifdef CONFIG_DEBUG_INFO
 ifdef CONFIG_DEBUG_INFO_SPLIT
-- 
2.18.4