The Linux/BSD DF kernel bug

Ove Kaaven ovek at
Thu Mar 20 05:33:45 CDT 2008

Alexandre Julliard skrev:
> Ove Kaaven <ovek at> writes:
>> Francois Gouget skrev:
>>> Does anyone know if MSVC does a cld in the right places?
>> Maybe. But it hardly matters. Only GCC-generated code is affected. The 
>> problem might then show up in Wine signal/exception handling. Things 
>> like, say, copying the CONTEXT structures around, for example.
> It matters in the sense that Wine currently doesn't clear the direction
> flag before calling an exception handler, so if MSVC doesn't do a cld
> then we'd have the same bug WRT msvc as the Linux kernel has WRT gcc.

But that's a bit of a different issue, unrelated to the kernel flaw. I 
was only talking about that flaw. I kind of tried to clarify that in my 
next followup... oh well.

When it comes to ABI issues with MSVC code, the question isn't so much 
whether it uses cld, but what Windows does when throwing exceptions. 
Does Windows clear the DF when it calls exception handlers? If not, then 
there's hardly any Wine bug here (that doesn't exist on Windows anyway). 
Perhaps someone should test, but my guess is that Windows doesn't clear it.

(And anyway, my experience is that MSVC assumes DF is undefined, and 
does the cld.)

> Of course now that gcc is changed we'll have to make sure to clear the
> flag regardless of what MSVC does.

But not just in the exception handling. Everywhere... there's no special 
case here.

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