On Aug 1 12:18, Jeremy Drake via Cygwin-patches wrote:
> This prevents memory corruption if a newer app or dll is used with an
> older cygwin dll. This is an unsupported scenario, but it's still a
> good idea to avoid corrupting memory if possible.
>
> Fixes: 7d5c55faa1 ("Cygwin: add wrappers for newer new/delete overloads")
> Co-authored-by: Corinna Vinschen <cori...@vinschen.de>
> Signed-off-by: Jeremy Drake <cyg...@jdrake.com>
> ---
>
> I left out initializing dll_major/dll_minor in dcrt0.cc as these fields
> are initialized in globals.cc already.
Oh, yeah, I didn't check that for my POC. But that means we can
do the same for api_major/api_minor (setting them in globals.cc,
that is).
> I also continue to update the
> __cygwin_cxx_malloc struct even though I don't think anything should be
> using it (rather the default_cygwin_cxx_malloc via the user_data pointer).
> It's not static for some reason, so something *could* be accessing it I
> guess.
I don't see how anything is supposed to access __cygwin_cxx_malloc.
You'd have to know the symbol name and what it is. Not even gcc
or libstdc++ use it.
So I wonder... rather than changing CONDITIONALLY_OVERRIDE, why don't
we just write to __cygwin_cxx_malloc and then change the pointer?
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?
> 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.
Thanks,
Corinna
