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kbuild: Only add -fno-var-tracking-assignments 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 2062afb4f8 ("Fix gcc-4.9.0 miscompilation of load_balance()
in scheduler") 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. 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>
Reviewed-by: Andi Kleen <andi@firstfloor.org>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
This commit is contained in:
Mark Wielaard 2020-10-17 14:01:35 +02:00 committed by Masahiro Yamada
parent 8402ee182c
commit 121c5d08d5
1 changed files with 5 additions and 1 deletions
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6
Makefile
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@ -814,7 +814,11 @@ 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 for GCC versions < 5.0
# https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61801
ifdef CONFIG_CC_IS_GCC
DEBUG_CFLAGS := $(call cc-ifversion, -lt, 0500, $(call cc-option, -fno-var-tracking-assignments))
endif
ifdef CONFIG_DEBUG_INFO