[PATCH 4/4] ntdll: Guard against syscall stack overrun.

[Paul Gofman]

On 4/16/22 21:59, Jin-oh Kang wrote:
> On Tue, Apr 12, 2022, 5:59 PM Paul Gofman <pgofman at codeweavers.com> wrote:
>
>     I don’t think this complication worth it. What we would like to
>     save is address space on 32 bit, but we can’t (before running 32
>     on 64 of course where this stack will be on 64 only). We
>     apparently need to reserve address space for stack at once, so it
>     has the space to grow, and then growing would only mean saving
>     committed pages.
>
>
> Maybe allocate extra stack only for function calls that might need it? 
> Something like this: 
> https://docs.microsoft.com/en-us/windows-hardware/drivers/ddi/ntddk/nf-ntddk-keexpandkernelstackandcallout
>
That can technically be made to work, but to do it we'd need:

- maintain some pool of larger thread kernel stacks;

- make a secondary switch to it in wine_unix_call or whenever we think 
we need a larger stack (as apparently it is not known in 
wine_syscall_dispatcher);

- hunt the functions requiring larger stack one by one.

All this together (and especially the last point) sounds like 
essentially a no go for me. Mind also that long term when 32 on 64 is on 
by default the syscall stack will exist on 64 only.
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