linux-kernel - Re: [PATCH v7 6/6] x86/vdso: Enable sframe generation in VDSO

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Message-ID: <9a63ce89-84f0-4782-90bf-dfd7c8ec8c52@linux.ibm.com>
Date: Fri, 6 Feb 2026 18:48:24 +0100
From: Jens Remus <jremus@...ux.ibm.com>
To: "H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org,
        linux-trace-kernel@...r.kernel.org, bpf@...r.kernel.org,
        x86@...nel.org, linux-mm@...ck.org,
        Steven Rostedt <rostedt@...nel.org>,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        Indu Bhagat <indu.bhagat@...cle.com>
Cc: Masami Hiramatsu <mhiramat@...nel.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...nel.org>,
        Jiri Olsa <jolsa@...nel.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andrii Nakryiko <andrii@...nel.org>,
        "Jose E. Marchesi" <jemarch@....org>,
        Beau Belgrave <beaub@...ux.microsoft.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Florian Weimer <fweimer@...hat.com>, Kees Cook <kees@...nel.org>,
        "Carlos O'Donell" <codonell@...hat.com>, Sam James <sam@...too.org>,
        Dylan Hatch <dylanbhatch@...gle.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        David Hildenbrand <david@...hat.com>,
        "Liam R. Howlett" <Liam.Howlett@...cle.com>,
        Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
        Michal Hocko
 <mhocko@...e.com>, Mike Rapoport <rppt@...nel.org>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Vlastimil Babka <vbabka@...e.cz>, Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        "Steven Rostedt (Google)" <rostedt@...dmis.org>
Subject: Re: [PATCH v7 6/6] x86/vdso: Enable sframe generation in VDSO

On 2/4/2026 1:49 AM, H. Peter Anvin wrote:
> On 2026-02-03 09:19, Jens Remus wrote:
>> -
>> +#if defined(__x86_64__) && defined(CONFIG_AS_SFRAME)

My understanding is that you would like above changed to:

#ifdef CONFIG_AS_SFRAME

>> +	.cfi_sections .eh_frame, .debug_frame, .sframe
>> +#else
>>  	.cfi_sections .eh_frame, .debug_frame
>> +#endif
>>  
> 
> It would be better to:
> 
> #undef CONFIG_AS_SFRAME	/* i386 doesn't support .sframe */
> 
> in fake_32bit_build.h.
Due to (binutils 2.46 pre-release) GNU assembler supporting --gsframe-3,
but only for x86-64 not for x86-32 (nor x32) CONFIG_AS_SFRAME is enabled
even for my i386 cross build attempt.  This then wrongly causes the
.cfi_sections with .sframe to be selected (verified by adding an #error
for testing).

IIUC the .cfi_sections is there to have DWARF in both .eh_frame and
.debug_frame.  For .sframe it basically has the same effect as
specifying the common assembler option --gsframe.  Given the more
specific option --gsframe-3 is explicitly specified I think it would
be better to drop the changes to both dwarf2.h and fake_32bit_build.h
and solely rely on --gsframe-3.

Josh, Indu, do you agree?

Thanks and rRegards,
Jens
-- 
Jens Remus
Linux on Z Development (D3303)
jremus@...ibm.com / jremus@...ux.ibm.com

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