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Date: Thu, 16 Mar 2006 14:03:38 -0500
From: Norton Allen <allen AT huarp DOT harvard DOT edu>
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Subject: RE: Bug in dlopen() (or following) code in Cygwin1.dll v 1.5.19-4
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Ah, got it--it behaves like exception handling, but it
doesn't *look* like exception handling. Seems like a
good place to add some comments! ;-) (Offer to submit
a patch, but seeing as I had to ask, I doubt I'm the
right person to do so.) Thanks for clearing this up
for me!

-Norton

On 16 March 2006, Dave Korn wrote:
> On 16 March 2006 15:48, Norton Allen wrote:
> 
> 
>>>> * thread.cc (verifyable_object_isvalid): check for
>>>> NULL object or reference
>>> 
>>> The "efault.faulted()" two lines above your change is supposed to catch
>>> NULL dereferences.
>> 
>> Whoa! This looks like voodoo action-at-a-distance. 
> 
>   Exception handling does that :)  See also setjmp/longjmp.
> 
>> efault.faulted()
>> doesn't even get passed the pointer to know whether or not it's
>> NULL. 
> 
>   errno doesn't get passed any pointers, but it still often ends up returning
> 'EINVAL' when the pointer you pass to a routine is null....
> 
>> Although efault.faulted() is supposed to catch the NULL dereferences,
> 
>   Nope, the exception handling is supposed to catch the NULL deref, and set an
> error code which is then returned by efault.faulted.
> 
>   Take a /look/ at the source for myfault::faulted in cygtls.h, it calls out
> to _cygtls::setup_fault, which calls _sjfault, which appears to be a q'n'd
> hacked-up version of setjmp in a context where it's going to get called back
> by an SEH handler.  So IIUIC, calling 'efault.faulted' will catch any
> exception that happens from the point of the call until the point where the
> efault object goes out of scope and gets destructed and will cause execution
> to jump back to the if... clause.
> 
> 
> 
> 

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