linux-kernel - Re: [RFC] Don't create sframes during build

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Message-ID: <jdw2iyr2dd6fzasbiwbzsaqohbi46hwd7wb3ze6qhztje2b6ld@qnween3ajj5e>
Date: Thu, 4 Sep 2025 10:14:09 -0700
From: Josh Poimboeuf <jpoimboe@...nel.org>
To: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc: Matthias Klose <doko@...ian.org>, linux-arch@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-kbuild@...r.kernel.org, Arnd Bergmann <arnd@...db.de>, 
	Peter Zijlstra <peterz@...radead.org>, Nathan Chancellor <nathan@...nel.org>, 
	Nicolas Schier <nicolas.schier@...ux.dev>, Binutils <binutils@...rceware.org>, 
	Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [RFC] Don't create sframes during build

On Thu, Sep 04, 2025 at 06:34:04PM +0200, Sebastian Andrzej Siewior wrote:
> On 2025-09-04 16:02:42 [+0200], Matthias Klose wrote:
> > [ CCing binutils@...rceware.org ]
> > 
> > On 9/4/25 15:18, Sebastian Andrzej Siewior wrote:
> > > Hi,
> > > 
> > > gcc in Debian, starting with 15.2.0-2, 14.3.0-6 enables sframe
> > > generation. Unless options like -ffreestanding are passed. Since this
> > > isn't done, there are a few warnings during compile
> > 
> > If there are other options when sframe shouldn't be enabled, please tell.
> 
> No, I think this is okay.
> 
> …
> > > We could drop the sframe during the final link but this does not get rid
> > > of the objtool warnings so we would have to ignore them. But we don't
> > > need it. So what about the following:
> > > 
> > > diff --git a/Makefile b/Makefile
> > > --- a/Makefile
> > > +++ b/Makefile
> > > @@ -886,6 +886,8 @@ ifdef CONFIG_CC_IS_GCC
> > >   KBUILD_CFLAGS	+= $(call cc-option,--param=allow-store-data-races=0)
> > >   KBUILD_CFLAGS	+= $(call cc-option,-fno-allow-store-data-races)
> > >   endif
> > > +# No sframe generation for kernel if enabled by default
> > > +KBUILD_CFLAGS	+= $(call cc-option,-Xassembler --gsframe=no)
> > >   ifdef CONFIG_READABLE_ASM
> > >   # Disable optimizations that make assembler listings hard to read.
> > This is what I chose for package builds that need disablement of sframe.
> 
> I think this would work for now. Longterm we would have to allow sframe
> creation and keep section if an architecture decides to use it for its
> backtracing. While orc seems fine on x86, there are arm64 patches to use
> for as a stack unwinder.

This is probably fine, but... how does this interact with other kernel
makefiles enabling sframe?  For example, x86 will soon have a patch to
enable sframe generation for vdso.  And as you mentioned, arm64 will
enable it kernel-wide.

Removing the objtool !ENDBR warnings would be trivial (and is a good
thing to do regardless).

-- 
Josh