linux-kernel - Re: [PATCH v4 17/39] unwind_user/sframe: Add support for reading .sframe headers

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <20250207211324.jwtyy3z5ud2jwegi@jpoimboe>
Date: Fri, 7 Feb 2025 13:13:24 -0800
From: Josh Poimboeuf <jpoimboe@...nel.org>
To: Jens Remus <jremus@...ux.ibm.com>
Cc: Andrii Nakryiko <andrii.nakryiko@...il.com>,
	Indu Bhagat <indu.bhagat@...cle.com>, x86@...nel.org,
	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, 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, Jordan Rome <jordalgo@...a.com>,
	Sam James <sam@...too.org>, linux-trace-kernel@...r.kernel.org,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Florian Weimer <fweimer@...hat.com>,
	Andy Lutomirski <luto@...nel.org>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Weinan Liu <wnliu@...gle.com>
Subject: Re: [PATCH v4 17/39] unwind_user/sframe: Add support for reading
 .sframe headers

On Wed, Feb 05, 2025 at 02:56:36PM +0100, Jens Remus wrote:
> On 29.01.2025 03:02, Josh Poimboeuf wrote:
> 
> > Note FDEs aren't even needed here as the unwinder doesn't need to know
> > when a function begins/ends.  The only info needed by the unwinder is
> > just the fre_data struct.  So a simple binary search of fres[] is all
> > that's really needed.
> 
> In SFrame V2 FDEs specify ranges bound by function start address and
> length.  FREs in contrast specify open ranges bounded by start address.
> Their effect ends either with the next FRE becoming into effect or when
> their FDE range ends.
> This concept enables holes in the .text section which do not have any
> valid FDE/FRE information associated.
> 
> Your proposal lacks some sort of mechanism to replicate those holes.
> It could be FDEs with a flag (or no offsets?) that specifies their
> range has no valid information.

In ORC, a hole is simply specified by an ORC entry (aka "FRE") of type
UNDEFINED.

That could be done here as well: the linker would replace a gap with an
"undefined" FRE which could be identified either by setting a bit in the
FRE header, or by using a special fre_data[] entry.  For example,
fre_data index 0 could just be a placeholder for the undefined FRE type.

-- 
Josh