linux-kernel - Re: [PATCH 1/8] unwind: build kernel with sframe info

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Message-ID: <20250207180157.j25afocbe2kkkbv3@jpoimboe>
Date: Fri, 7 Feb 2025 10:01:57 -0800
From: Josh Poimboeuf <jpoimboe@...nel.org>
To: Indu Bhagat <indu.bhagat@...cle.com>
Cc: Weinan Liu <wnliu@...gle.com>, Steven Rostedt <rostedt@...dmis.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Mark Rutland <mark.rutland@....com>, roman.gushchin@...ux.dev,
	Will Deacon <will@...nel.org>, Ian Rogers <irogers@...gle.com>,
	linux-toolchains@...r.kernel.org, linux-kernel@...r.kernel.org,
	live-patching@...r.kernel.org, joe.lawrence@...hat.com,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 1/8] unwind: build kernel with sframe info

On Tue, Feb 04, 2025 at 04:22:27PM -0800, Indu Bhagat wrote:
> > +++ b/arch/Kconfig
> > @@ -1736,4 +1736,12 @@ config ARCH_WANTS_PRE_LINK_VMLINUX
> >   	  An architecture can select this if it provides arch/<arch>/tools/Makefile
> >   	  with .arch.vmlinux.o target to be linked into vmlinux.
> > +config AS_HAS_SFRAME_SUPPORT
> > +	# Detect availability of the AS option -Wa,--gsframe for generating
> > +	# sframe unwind table.
> > +	def_bool $(cc-option,-Wa$(comma)--gsframe)
> > +
> 
> Since the version of an admissible SFrame section needs to be atleast
> SFRAME_VERSION_2, it will make sense to include SFrame version check when
> detecting compatible toolchain.

Also, Jens pointed out that checking for '-Wa,--gsframe' isn't
sufficient, as it still succeeds for architectures that aren't yet
supported:

  https://lore.kernel.org/b89bcb68-d010-4041-aacf-15b934675705@linux.ibm.com

so in my patches I have:

config AS_SFRAME
	def_bool $(as-instr,.cfi_sections .sframe\n.cfi_startproc\n.cfi_endproc)

Though I'm not sure how you would add an SFrame version check to that.

-- 
Josh