From 377ccbb483738f84400ddf5840c7dd8825716985 Mon Sep 17 00:00:00 2001 From: Steven Rostedt <rostedt@goodmis.org> Date: Thu, 28 Jul 2016 22:30:43 -0400 Subject: [PATCH] Makefile: Mute warning for __builtin_return_address(>0) for tracing only With the latest gcc compilers, they give a warning if __builtin_return_address() parameter is greater than 0. That is because if it is used by a function called by a top level function (or in the case of the kernel, by assembly), it can try to access stack frames outside the stack and crash the system. The tracing system uses __builtin_return_address() of up to 2! But it is well aware of the dangers that it may have, and has even added precautions to protect against it (see the thunk code in arch/x86/entry/thunk*.S) Linus originally added KBUILD_CFLAGS that would suppress the warning for the entire kernel, as simply adding KBUILD_CFLAGS to the tracing directory wouldn't work. The tracing directory plays a bit with the CFLAGS and requires a little more logic. This adds that special logic to only suppress the warning for the tracing directory. If it is used anywhere else outside of tracing, the warning will still be triggered. Link: http://lkml.kernel.org/r/20160728223043.51996267@grimm.local.home Tested-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Steven Rostedt <rostedt@goodmis.org> --- Makefile | 1 - kernel/trace/Makefile | 4 ++++ 2 files changed, 4 insertions(+), 1 deletion(-) diff --git a/Makefile b/Makefile index 393b6159ae924..d384848478b94 100644 --- a/Makefile +++ b/Makefile @@ -620,7 +620,6 @@ include arch/$(SRCARCH)/Makefile KBUILD_CFLAGS += $(call cc-option,-fno-delete-null-pointer-checks,) KBUILD_CFLAGS += $(call cc-disable-warning,maybe-uninitialized,) -KBUILD_CFLAGS += $(call cc-disable-warning,frame-address,) ifdef CONFIG_CC_OPTIMIZE_FOR_SIZE KBUILD_CFLAGS += -Os diff --git a/kernel/trace/Makefile b/kernel/trace/Makefile index 979e7bfbde7a8..d0a1617b52b48 100644 --- a/kernel/trace/Makefile +++ b/kernel/trace/Makefile @@ -1,4 +1,8 @@ +# We are fully aware of the dangers of __builtin_return_address() +FRAME_CFLAGS := $(call cc-disable-warning,frame-address) +KBUILD_CFLAGS += $(FRAME_CFLAGS) + # Do not instrument the tracer itself: ifdef CONFIG_FUNCTION_TRACER -- GitLab