linux-kernel - Re: [PATCH v8 6/6] x86/vdso: Enable sframe generation in VDSO

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Message-ID: <8929995D-26A5-4F57-A41D-634CEB3D7C29@zytor.com>
Date: Tue, 10 Feb 2026 10:49:21 -0800
From: "H. Peter Anvin" <hpa@...or.com>
To: Jens Remus <jremus@...ux.ibm.com>, linux-kernel@...r.kernel.org,
        linux-trace-kernel@...r.kernel.org, bpf@...r.kernel.org,
        x86@...nel.org, linux-mm@...ck.org,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        Steven Rostedt <rostedt@...nel.org>
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>,
        Indu Bhagat <indu.bhagat@...cle.com>,
        "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@...nel.org>,
        "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 v8 6/6] x86/vdso: Enable sframe generation in VDSO

On February 10, 2026 8:46:33 AM PST, Jens Remus <jremus@...ux.ibm.com> wrote:
>On 2/6/2026 8:36 PM, Jens Remus wrote:
>> From: Josh Poimboeuf <jpoimboe@...nel.org>
>> 
>> Enable sframe generation in the VDSO library so kernel and user space
>> can unwind through it.
>> 
>> SFrame isn't supported for x32 or x86-32.  Discard .sframe sections for
>> those VDSOs.
>> 
>> [ Jens Remus: Add support for SFrame V3.  Prevent GNU_SFRAME program
>> table entry to empty .sframe section. ]
>> 
>> Signed-off-by: Josh Poimboeuf <jpoimboe@...nel.org>
>> Signed-off-by: Steven Rostedt (Google) <rostedt@...dmis.org>
>> Signed-off-by: Jens Remus <jremus@...ux.ibm.com>
>
>> diff --git a/arch/Kconfig b/arch/Kconfig
>
>> @@ -479,6 +479,13 @@ config HAVE_HARDLOCKUP_DETECTOR_ARCH
>>  	  It uses the same command line parameters, and sysctl interface,
>>  	  as the generic hardlockup detectors.
>>  
>> +config AS_SFRAME
>> +	bool
>> +
>> +config AS_SFRAME3
>> +	def_bool $(as-instr,.cfi_startproc\n.cfi_endproc,-Wa$(comma)--gsframe-3)
>
>Above tests whether the assembler supports --gsframe-3 to generate
>.sframe in SFrame V3 format.  GNU assembler only supports to generate
>SFrame for x86-64.  If the assembler is built for i386 (x86-32) the test
>will fail unless option --64 is specified.  I wonder whether that could
>happen in (the rather hypothetical?) case, when the kernel is cross built
>for x86-64 on i386?  Should this therefore be changed to the following?
>
>config AS_SFRAME_64
>	def_bool $(as-instr,.cfi_startproc\n.cfi_endproc,$(m64-flag) -Wa$(comma)--gsframe)
>
>An alternative would be to enable as-instr64 to accept an optional flag
>operand, similar to as-instr, and use as-instr64 instead of as-instr.
>
>Or is this not required, as in a cross build for 64-bit on a 32-bit
>platform (or inverse) a respective cross toolchain is a prerequisite and
>the m64-flag (or m32-flag) is not used?
>
>I tried to simulate this using docker and an i386 image and then using
>the i386 tool in the container to switch "uname -m" to "i686".  But both
>of my following attempts to build for x86-64 on i386 fail with fixdep
>not found:
>
>$ docker run -it --rm -v "$HOME/linux:$HOME/linux" --platform i386 public.ecr.aws/docker/library/debian:13.3
># sed -i -s 's/^Types: deb/& deb-src/' /etc/apt/sources.list.d/debian.sources
># apt update
># apt -y build-dep linux
>
># make mrproper
># i386 make ARCH=x86_64 defconfig
># i386 make ARCH=x86_64 arch/x86/entry/vdso/
>
># make mrproper
># apt -y install gcc-x86-64-linux-gnu
># i386 make ARCH=x86_64 CROSS_COMPILE=x86_64-linux-gnu- defconfig
># i386 make ARCH=x86_64 CROSS_COMPILE=x86_64-linux-gnu- arch/x86/entry/vdso/
>
>> +	select AS_SFRAME
>> +
>>  config UNWIND_USER
>>  	bool
>
>> diff --git a/arch/x86/entry/vdso/vdso64/Makefile b/arch/x86/entry/vdso/vdso64/Makefile
>
>> @@ -14,6 +14,7 @@ vobjs-$(CONFIG_X86_SGX)		+= vsgx.o
>>  
>>  # Compilation flags
>>  flags-y				:= -DBUILD_VDSO64 -m64 -mcmodel=small
>> +flags-$(CONFIG_AS_SFRAME3)	+= -Wa,--gsframe-3
>
>flags-$(CONFIG_AS_SFRAME3_64)	+= -Wa,--gsframe-3
>
>>  
>>  # The location of this include matters!
>>  include $(src)/../common/Makefile.include
>Thanks and regards,
>Jens

I think we can worry about that later.