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Date: Mon, 28 Jul 2025 11:18:35 +0200
To: cygwin AT cygwin DOT com
Subject: Re: new c++ new/delete overloads need wrapping?
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From: Corinna Vinschen via Cygwin <cygwin AT cygwin DOT com>
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On Jul 25 10:28, Jeremy Drake via Cygwin wrote:
> On Fri, 25 Jul 2025, Corinna Vinschen via Cygwin wrote:
> > Nevertheless, the code overriding the members in per_process_cxx_malloc
> > is living in the app (_cygwin_crt0_common.cc).  If you just append members
> > to per_process_cxx_malloc nad implement the wrappers in cxx.cc and
> > libstdcxx_wrapper.cc, then old apps using the old _cygwin_crt0_common.cc
> > will just not see the new functions.  So that should work out of the
> > box, shouldn't it?
> 
> I missed a pointer dereference in _cygwin_crt0_common.cc that meant the
> struct was being copied rather than the pointer replaced.  I was concerned
> that a pointer to the old struct might be used, and garbage found in the
> new fields.  I see now that it copies the contents, and if the struct is
> smaller it will obviously leave the new fields alone.
> 
> I came across this comment that concerned me though
>   /* Broken DLLs built against Cygwin versions 1.7.0-49 up to 1.7.0-57
>      [...]
> I don't see the save and restore mentioned in dlopen...  Are these old
> DLLs sufficiently old that there wasn't 64-bit yet, and therefore can't be
> used anymore?

Indeed, the comment is a remnant from our 32 bit past.  Cygwin 1.7.0 was
from 2009, while we merged the 64 bit stuff into the tree in 2013 and
the first official version supporting x86_64 was 1.7.19, I think.


Corinna

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