diff mbox series

Only add -fno-var-tracking-assignments workaround for old GCC versions.

Message ID 20201014110132.2680-1-mark@klomp.org (mailing list archive)
State New, archived
Headers show
Series Only add -fno-var-tracking-assignments workaround for old GCC versions. | expand

Commit Message

Mark Wielaard Oct. 14, 2020, 11:01 a.m. UTC 
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@klomp.org>
Acked-by: Ian Rogers <irogers@google.com>
Cc: linux-toolchains@vger.kernel.org
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Nick Desaulniers <ndesaulniers@google.com>
Cc: Segher Boessenkool <segher@kernel.crashing.org>
Cc: Florian Weimer <fw@deneb.enyo.de>
---
 Makefile | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

Comments

Andi Kleen Oct. 14, 2020, 3:17 p.m. UTC | #1 
On Wed, Oct 14, 2020 at 01:01:32PM +0200, Mark Wielaard wrote:
> 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.

Add

... This allows various tools such as a perf probe or gdb debuggers
or systemtap to resolve variable locations using dwarf locations in 
more code.
> 
> Signed-off-by: Mark Wielaard <mark@klomp.org>
> Acked-by: Ian Rogers <irogers@google.com>
> Cc: linux-toolchains@vger.kernel.org
> Cc: Andi Kleen <andi@firstfloor.org>
> Cc: Nick Desaulniers <ndesaulniers@google.com>
> Cc: Segher Boessenkool <segher@kernel.crashing.org>
> Cc: Florian Weimer <fw@deneb.enyo.de>

Reviewed-by: Andi Kleen <ak@linux.intel.com>

-Andi
diff mbox series

Patch

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