On 24/02/2010 04:52, Dave Korn wrote:
> I think the answer lies here, in this comment in dll_dllcrt0_1:
>
>> /* Make sure that our exception handler is installed.
>> That should always be the case but this just makes sure.
>>
>> At some point, we may want to just remove this code since
>> the exception handler should be guaranteed to be installed.
>> I'm leaving it in until potentially after the release of
>> 1.7.1 */
>> _my_tls.init_exception_handler (_cygtls::handle_exceptions);
>
> Well, it may or may not already be installed, depending whether we got here
> via dlopen or whether this is a statically-linked DLL being initialised at
> process startup, and if it is already installed, it's not at the front of the
> list. So I figure the best bet would be to replace this call with a local
> stack-frame-based exception registration record, which we'll unlink if we
> return. IOW, just the same thing as those OS-registered SEH frames are doing
> when they unwind. I'll report back later if it works.
Yeh, that works nicely. Here's what I tested, along with a couple of extra
test cases I used to check whether exception handling was still working before
and after the dlopen call. With the current state of HEAD, the first one
works (by which I mean "prints 'sig 11' forever" and the second one fails (by
which I means reaches some sort of exit without hitting the signal handler at
all). With the attached diff, they both work (as does the original unmodified
testcase).
This is just a brain dump because I'm off to bed now, hence no change log,
and there's still commented-out stuff and inadequate commenting, but I figured
I may as well let everyone know what I found out. 'night all!
cheers,
DaveK
Index: winsup/cygwin/dll_init.cc
===================================================================
RCS file: /cvs/src/src/winsup/cygwin/dll_init.cc,v
retrieving revision 1.70
diff -p -u -r1.70 dll_init.cc
--- winsup/cygwin/dll_init.cc 5 Feb 2010 15:05:22 -0000 1.70
+++ winsup/cygwin/dll_init.cc 24 Feb 2010 05:05:45 -0000
@@ -329,7 +329,14 @@ dll_dllcrt0_1 (VOID *x)
the exception handler should be guaranteed to be installed.
I'm leaving it in until potentially after the release of
1.7.1 */
- _my_tls.init_exception_handler (_cygtls::handle_exceptions);
+ /* _my_tls.init_exception_handler (_cygtls::handle_exceptions); */
+ /* Correction: install a temporary registration with our handler
+ at the head of the list, and unlink it before returning. */
+ extern exception_list *_except_list asm ("%fs:0");
+ exception_list seh;
+ seh.handler = _cygtls::handle_exceptions;
+ seh.prev = _except_list;
+ _except_list = &seh;
if (p == NULL)
p = &__cygwin_user_data;
@@ -390,6 +397,8 @@ dll_dllcrt0_1 (VOID *x)
res = -1;
else
res = (DWORD) d;
+
+ _except_list = seh.prev;
}
/* OBSOLETE: This function is obsolete and will go away in the
#include <dlfcn.h>
#include <signal.h>
#include <stdio.h>
void my_handler (int sig)
{
printf ("sig %d\n", sig);
}
int main( int argc, char** argv )
{
signal (SIGSEGV, my_handler);
*(volatile unsigned int *)0;
void* dll = dlopen( "mutex.dll", RTLD_NOW );
dlclose( dll );
}
#include <dlfcn.h>
#include <signal.h>
#include <stdio.h>
void my_handler (int sig)
{
printf ("sig %d\n", sig);
}
int main( int argc, char** argv )
{
signal (SIGSEGV, my_handler);
void* dll = dlopen( "mutex.dll", RTLD_NOW );
*(volatile unsigned int *)0;
dlclose( dll );
}
--
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