linux-kernel - Re: warning: calling ‘__builtin_return_address’ with a nonzero argument is unsafe

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Date:	Thu, 28 Jul 2016 22:30:43 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Josh Poimboeuf <jpoimboe@...hat.com>,
	Ingo Molnar <mingo@...hat.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: warning: calling ‘__builtin_return_address’ with a nonzero argument is unsafe

On Thu, 28 Jul 2016 18:25:33 -0700
Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> I tried something like that, but the CFLAGS games the tracing code
> does made my thing result in
> 
>   kernel/trace/Makefile:20: *** Recursive variable 'KBUILD_CFLAGS'
> references itself (eventually).  Stop.
> 
> but yes, if you have the magic fingers to make it work, limiting the
> -Wno-frame-address to just the tracing code sounds like the
> RightThing(tm).

Take 2:

It compiles for me, but I don't have a compiler that has that warning
to test with. See if this works. BTW, it looks like that last comma
before the ending parenthesis is not needed.

Signed-off-by: Steven Rostedt <rostedt@...dmis.org>
---
diff --git a/Makefile b/Makefile
index 393b615..d384848 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 979e7bf..d0a1617 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