x86/build: convert function graph '-Os' error to warning
For pre-4.6.0 versions of GCC, which don't have '-mfentry', the
'-maccumulate-outgoing-args' option is required for function graph
tracing in order to avoid GCC bug 42109.
However, GCC ignores '-maccumulate-outgoing-args' when '-Os' is
also set.
Currently we force a build error to prevent that scenario, but that
breaks randconfigs. So change the error to a warning which also
disables CONFIG_CC_OPTIMIZE_FOR_SIZE.
Reported-by: Andi Kleen <andi@firstfloor.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: kbuild test robot <fengguang.wu@intel.com>
Cc: kbuild-all@01.org
Link: http://lkml.kernel.org/r/20170418214429.o7fbwbmf4nqosezy@treble
Signed-off-by: Ingo Molnar <mingo@kernel.org>
diff --git a/arch/x86/Makefile b/arch/x86/Makefile
index a94a4d1..49d160b 100644
--- a/arch/x86/Makefile
+++ b/arch/x86/Makefile
@@ -154,6 +154,14 @@
else
ifeq ($(call cc-option-yn, -mfentry), n)
ACCUMULATE_OUTGOING_ARGS := 1
+
+ # GCC ignores '-maccumulate-outgoing-args' when used with '-Os'.
+ # If '-Os' is enabled, disable it and print a warning.
+ ifdef CONFIG_CC_OPTIMIZE_FOR_SIZE
+ undefine CONFIG_CC_OPTIMIZE_FOR_SIZE
+ $(warning Disabling CONFIG_CC_OPTIMIZE_FOR_SIZE. Your compiler does not have -mfentry so you cannot optimize for size with CONFIG_FUNCTION_GRAPH_TRACER.)
+ endif
+
endif
endif
endif
