Re: [perl #133327] stack checks make -DDEBUGGING builds incompatiblewith normal ones

On Tue, Jul 03, 2018 at 08:49:39AM -0700, Niko Tyni (via RT) wrote:
> The stack 'high water mark' checks introduced in v5.27.1-66-g87058c31e9
> seem to have introduced an incompatibility when XS modules are built
> with a normal Perl but run with a (otherwise similarly configured)
> -DDEBUGGING Perl.
> 
> We're using this combination in Debian as we offer a -DDEBUGGING
> interpreter (called /usr/bin/debugperl) in a separate package for the
> benefit of our users, but we don't rebuild all the XS modules with that.
[snip]
> If I grok this correctly, the problem is that EXTEND only updates
> the high-water mark when the DEBUGGING preprocessor symbol is defined
> (i.e. the choice is done at compile time.) If the XS module is built
> without -DDEBUGGING in ccflags (as is the case for Debian XS module
> packages), the high-water mark doesn't get updated.  If the interpreter
> side is built with -DDEBUGGING (as our debugperl is), it will still
> check the hwm, resulting in the panic.
> 
> Would it be feasible move the -DDEBUGGING check in EXTEND to run time,
> for instance by calling a function that's a no-op in non-DEBUGGING
> interpreters, or checking for an interpreter variable that's only set
> in -DDEBUGGING builds? This has a runtime cost, but I'm not sure how
> significant that is?

I wouldn't like any solution that adds extra run-time overhead to
non-debugging-build XS modules.

To avoid that, the debugging part of the perl interperter would need to be
able to determine when it calls an XS sub or a non-core pp_foo() function,
whether that code what compiled under DEBUGGING. I can't think of a way to
determine this.

A fall-back position would be to add support for a PERL_NO_STACK_HWM_CHECK
define / build option which would completely disable checks, even if
the core was built with DEBUGGING. That would of course disable
the check even for XS modules built with DEBUGGING.

-- 
Overhead, without any fuss, the stars were going out.
    -- Arthur C Clarke

• [perl #133327] stack checks make -DDEBUGGING builds incompatiblewith normal ones by bulk88 via RT
• [perl #133327] stack checks make -DDEBUGGING builds incompatiblewith normal ones by Sergey Aleynikov via RT
• [perl #133327] stack checks make -DDEBUGGING builds incompatiblewith normal ones by Niko Tyni
• Re: [perl #133327] stack checks make -DDEBUGGING builds incompatiblewith normal ones by Dave Mitchell
• Re: [perl #133327] stack checks make -DDEBUGGING builds incompatiblewith normal ones by Niko Tyni