Re: feature/asan-gc-poisoning: Better memory checks using AddressSanitizer

[Vibhav Pant <vibhavp@gmail.com>]

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Unless there are any objections, I plan to merge this branch into master
today.

Thanks,
Vibhav

Vibhav Pant
vibhavp@gmail.com

On Tue, Dec 6, 2022, 02:05 Vibhav Pant <vibhavp@gmail.com> wrote:

> As part of trying to debug the deluge of GC borks in
> scratch/comp-static-data, I took a slight detour through Emacs' memory
> management code and the sanity checks that it optionally comes with.
> The changes in feature/asan-gc-poisoning attempt to augment the
> latter, specifically when Emacs is built with '-fsanitize=address'.
>
> When enabled, almost all memory management operations are instrumented
> with calls to ASan's "(un)poisoning" functions, which allow ASan to
> mark allocated but not freed addresses as "poisoned", triggering
> errors whenever they have been accessed. The idea behind this is to
> add another layer of checks against code that makes use of free lists
> and arena based allocators, only allowing access to regions of the
> memory that are actually intended to be accessible (aka "unpoisoned"
> in ASan parlance) by non alloc-related C code. An instance of this is
> any object on a free list, or a vectorlike with the type PVEC_FREE (we
> do abort whenever we come across such a vector, but this ideally
> catches the bug way earlier in the flow, and therefore closer to the
> source of the actual problem). Additional documentation explaining
> this feature is available both on src/alloc.c and the "Running Emacs
> with address sanitization" section in etc/DEBUG.
>
> The branch bootstraps successfully both with native-comp enabled and
> disabled, and passes everything on the test suite on my machine.
> Because enabling Address Sanitizer comes with a significant
> performance + memory overhead, using it as a daily driver isn't
> without a decent bit of sluggishness, although building with -O2 and
> native compilation seems to help, at least a little.
> I plan to get install this in `master` soon, so both feedback and
> testing from other users would be greatly appreciated. The current
> codebase quite likely does everything alloc related correctly, so an
> ASan error might be indicative of a snag in this branch instead of
> Emacs itself (fingers crossed for the opposite, however :)).
>
> Thanks,
> Vibhav
> --
> Vibhav Pant
> vibhavp@gmail.com
> GPG: 7ED1 D48C 513C A024 BE3A  785F E3FB 28CB 6AB5 9598
>

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