[Bug dynamic-link/30127] [rfe]: enable ld audit at run-time

["janderson at rice dot edu" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=30127

--- Comment #49 from Jonathon Anderson <janderson at rice dot edu> ---
(In reply to Stas Sergeev from comment #46)
> So let me summarize that memfd_create()
> (shm_open() actually) is not a replacement,
> but rather is an essential part of the
> scheme. Using it together with la_premap_dlmem()
> and la_premap() you can get the desired
> picture. Desired picture is 2 identical
> mappings of the same lib, one at relolc_addr,
> one at mmap_addr=reloc_addr+VM_window_start.
> 
> There is basically nothing else!
> That scheme is very simple to describe,
> but not that simple to grok from that
> description, as no one have tried that
> layout yet.
FWIW I understand this succinct description of your intended use case much
better than your prior descriptions, thanks. If this is the core feature you
need, then I see where most of my questions about the VM go off-topic. Sorry
for the noise. (I honestly thought you were trying to achieve something far
more drastic...)

So in short, dynamic auditor loading is merely a "detail" in your full
approach, since you don't have access to the executable or pre-launch
environment and your patch to implement this core feature uses LD_AUDIT to host
the object mmap callback.

I'll redirect my thoughts that are really about object mapping over to
https://sourceware.org/bugzilla/show_bug.cgi?id=30007. I think it makes sense
to resolve that RFE first, since that is in fact the core feature you need for
your entire approach to function. After (or maybe in parallel with) that we can
continue to discuss dynamic auditor loading over here.

(In reply to Stas Sergeev from comment #47)
> But regarding the dlmem()&co impl itself -
> I'll rewrite it when this dlload_audit_module()
> patch settles, as I definitely know more
> about glibc than back when dlmem() was written.
> So no need to look into it or criticise
> it just yet. :) If you do look, please
> restrict to a test-cases.
Certainly, I'll stick to the API and test cases. :D

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