linux-kernel - Re: [PATCH v3 09/19] unwind: Introduce sframe user space unwinding

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Message-ID: <20241101213518.GX29862@gate.crashing.org>
Date: Fri, 1 Nov 2024 16:35:18 -0500
From: Segher Boessenkool <segher@...nel.crashing.org>
To: Josh Poimboeuf <jpoimboe@...nel.org>
Cc: Andrii Nakryiko <andrii.nakryiko@...il.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, Indu Bhagat <indu.bhagat@...cle.com>,
        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.kerne.org,
        Jens Remus <jremus@...ux.ibm.com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Florian Weimer <fweimer@...hat.com>, Andy Lutomirski <luto@...nel.org>
Subject: Re: [PATCH v3 09/19] unwind: Introduce sframe user space unwinding

Hi!

On Fri, Nov 01, 2024 at 12:48:00PM -0700, Josh Poimboeuf wrote:
> On Fri, Nov 01, 2024 at 12:35:13PM -0700, Josh Poimboeuf wrote:
> > On Fri, Nov 01, 2024 at 12:33:07PM -0700, Josh Poimboeuf wrote:
> > > On Fri, Nov 01, 2024 at 02:09:08PM -0500, Segher Boessenkool wrote:
> > > > On Thu, Oct 31, 2024 at 04:03:13PM -0700, Josh Poimboeuf wrote:
> > > > > Actually I just double checked and even the kernel's ELF loader assumes
> > > > > that each executable has only a single text start+end address pair.
> > > > 
> > > > Huh?  What makes you think that?  There can be many executable PT_LOAD
> > > > segments in each and every binary.
> > > 
> > > Right, but for executables (not shared libraries) the kernel seems to
> > > assume they're contiguous?  See the 'start_code' and 'end_code'
> > > variables in load_elf_binary() load_elf_interp().
> > 
> > Typo, see load_elf_binary (not load_elf_interp).
> 
> Hm, actually AFAICT that's only for reporting things in sysfs/proc.  So
> maybe it's assumed but not really "enforced".

Yes, this is copied to mm->start_code (etc.)  This isn't used for
anything very important it seems, it seems to be a leftover from when we
only had really simple binfmts?  For a.out it did actually make sense,
for example :-)


Segher