GNU bug report logs - #76393
Warn about -fsanitizer=address builds

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From: Eli Zaretskii <eliz <at> gnu.org>
To: pipcet <at> protonmail.com, Paul Eggert <eggert <at> cs.ucla.edu>
Cc: 76393 <at> debbugs.gnu.org
Subject: bug#76393: Warn about -fsanitizer=address builds
Date: Sat, 01 Mar 2025 14:18:58 +0200

Ping!  Can we make progress with this issue, please?

> Date: Tue, 18 Feb 2025 16:50:14 -0800
> Cc: 76393 <at> debbugs.gnu.org, Eli Zaretskii <eliz <at> gnu.org>
> From: Paul Eggert <eggert <at> cs.ucla.edu>
> 
> On 2/18/25 07:48, Pip Cet wrote:
> >   Building Emacs with address sanitization can help debug memory-use
> > -problems, such as freeing the same object twice.  To use
> > -AddressSanitizer with GCC and similar compilers, append
> > +problems, such as freeing the same object twice.  However,
> > +-fsanitize=address also introduces bugs in the compiled code which cause
> > +GC problems and phantom crashes, which do not always look like they're
> > +caused by the address sanitizer.
> 
> I don't see a GCC bug there. What I see is an incompatibility with 
> Emacs's garbage collector, a collector which relies on several aspects 
> of undefined behavior in C. So I suggest changing the last three lines 
> to something like this:
> 
> as the default behavior of -fsanitize=address is incompatible with 
> ordinary Emacs operation, it needs to be combined with other options.
> 
> 
> > +ASAN_OPTIONS='detect_stack_use_after_return=0,detect_leaks=0' in the
> > +environment to suppress diagnostics of minor memory leaks in Emacs, and
> > +buggy code which relocates objects from the stack to the heap .  For
> > +example:
> 
> Here, change "buggy code which relocates" to "to suppress relocation 
> of". Also, omit the space before ".".
> 
> Otherwise, it looks good.
> 
> I've found -fsanitize=address to be verrrrry helpful when debugging 
> obscure memory problems, and it's good to document how to use it.
> 
> It would be even better if we changed Emacs so that ASAN_OPTIONS need 
> not contain set detect_stack_use_after_return=0, as that would help 
> detect more errors. -fsanitize=address has support for this sort of 
> thing; see its __asan_addr_is_in_fake_stack function. However, Emacs 
> currently doesn't use that support, so we must currently settle for 
> detect_stack_use_after_return=0.
> 

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