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 2062afb ("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 <[email protected]> Acked-by: Ian Rogers <[email protected]> Reviewed-by: Andi Kleen <[email protected]> Signed-off-by: Masahiro Yamada <[email protected]>
chewitt · Oct 20, 2020 · 121c5d0 · 121c5d0
1 parent 8402ee1
commit 121c5d0
Showing 1 changed file with 5 additions and 1 deletion.
diff --git a/Makefile b/Makefile
@@ -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