On Aug 2 10:53, Jeremy Drake via Cygwin-patches wrote:
> On Sat, 2 Aug 2025, Corinna Vinschen wrote:
> > There's no good reason that user_data->cxx_malloc points to
> > default_cygwin_cxx_malloc, other than to prime __cygwin_cxx_malloc.
> >
> > And then we could just
> >
> > newu->cxx_malloc = &__cygwin_cxx_malloc;
> >
> > This survives fork, but not execve. Do you see any reason
> > that we shouldn't just overwrite user_data->cxx_malloc as above?
>
> The comments suggest that it used to do that, but a prior bug resulted in
> it being changed to what it is now. I'd be concerned if the struct is
> expanded again in future that you'd have a hard time telling which version
> of the struct the pointer happens to point to when DLLs built with
> different versions of startup code are loaded in the same process. I'd
> rather keep it pointing tothe default_cygwin_cxx_malloc struct to be safe.
ACK
>
> > > diff --git a/winsup/cygwin/lib/_cygwin_crt0_common.cc
> > > b/winsup/cygwin/lib/_cygwin_crt0_common.cc
> > > index 5900e6315d..87f3e8042b 100644
> > > --- a/winsup/cygwin/lib/_cygwin_crt0_common.cc
> > > +++ b/winsup/cygwin/lib/_cygwin_crt0_common.cc
> > > @@ -124,6 +124,9 @@ _cygwin_crt0_common (MainFunc f, per_process *u)
> > > {
> > > per_process *newu = (per_process *) cygwin_internal (CW_USER_DATA);
> > > bool uwasnull;
> > > + bool new_dll_with_additional_operators =
> > > + newu ? CYGWIN_VERSION_CHECK_FOR_CXX17_OVERLOADS (newu)
> > > + : false;
> >
> > On second thought, why do we check newu for being not NULL again?
> > I added a comment to lib/_cygwin_crt0_common.cc back in 2009:
> >
> > newu is the Cygwin DLL's internal per_process and never NULL
> >
> > but never followed up on this. We can be sure that newu is non-NULL
> > *and* we can be sure that newu->cxx_malloc is non-NULL. In contrast
> > to u and u->cxx_malloc, but those are never referenced.
>
> I'll drop those checks.
Thanks,
Corinna
