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From: Segher Boessenkool <segher@kernel.crashing.org>
To: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: Andrii Nakryiko <andrii.nakryiko@gmail.com>, x86@kernel.org,
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Subject: Re: [PATCH v3 09/19] unwind: Introduce sframe user space unwinding
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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