linux-kernel - Re: [PATCH RFC 09/10] unwind: Introduce SFrame user space unwinding

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Date:   Thu, 9 Nov 2023 11:37:59 -0800
From:   Josh Poimboeuf <jpoimboe@...nel.org>
To:     Indu Bhagat <indu.bhagat@...cle.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...nel.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        linux-kernel@...r.kernel.org, x86@...nel.org,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Ian Rogers <irogers@...gle.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        linux-perf-users@...r.kernel.org, Mark Brown <broonie@...nel.org>,
        linux-toolchains@...r.kernel.org
Subject: Re: [PATCH RFC 09/10] unwind: Introduce SFrame user space unwinding

On Thu, Nov 09, 2023 at 11:31:59AM -0800, Indu Bhagat wrote:
> > +	if (shdr.preamble.magic != SFRAME_MAGIC ||
> > +	    shdr.preamble.version != SFRAME_VERSION_1 ||
> > +	    (!shdr.preamble.flags & SFRAME_F_FDE_SORTED) ||
> > +	    shdr.auxhdr_len || !shdr.num_fdes || !shdr.num_fres ||
> > +	    shdr.fdes_off > shdr.fres_off) {
> > +		return -EINVAL;
> > +	}
> > +
> 
> I would say that it will be ideal to start the support with SFRAME_VERSION_2
> onwards, if we have a choice.
> 
> The structure SFrame FDE in SFRAME_VERSION_1 was unaligned on-disk.  We
> fixed that in SFRAME_VERSION_2 (Binutils 2.41) by adding some padding as you
> have already noted. For x86_64, its not an issue though, yes.

Agreed.  I actually had v2 implemented but then realized my binutils was
older so I changed to v1 for testing.  But yeah, we can make v2 the
minimum.

-- 
Josh