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

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Date:	Wed, 27 Jul 2016 23:52:33 -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 Wed, 27 Jul 2016 20:21:50 -0700
Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> On Wed, Jul 27, 2016 at 6:58 PM, Steven Rostedt <rostedt@...dmis.org> wrote:
> > On Wed, 27 Jul 2016 16:00:54 -0700
> > Linus Torvalds <torvalds@...ux-foundation.org> wrote:  
> >>
> >> I can just add a
> >>
> >>   KBUILD_CFLAGS  += $(call cc-disable-warning,frame-address,)  
> >
> > I like this solution.  
> 
> Ok. Pushed out. As long as people are aware of this, and are hopefully
> at least looking for potential alternatives, it's fine.

I just looked at your patch. Would this work if you moved that
KBUILD_CFLAGS to the tracing directory? Something like the below (never
compiled or tested).

This way we still get warnings from other users.

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..48079dd 100644
--- a/kernel/trace/Makefile
+++ b/kernel/trace/Makefile
@@ -1,4 +1,7 @@
 
+# We are fully aware of the dangers of __builtin_return_address() > 0
+KBUILD_CFLAGS += $(call cc-disable-warning,frame-address,)
+
 # Do not instrument the tracer itself:
 
 ifdef CONFIG_FUNCTION_TRACER