Re: cyggfortran-3.dll broken ?

[Don Ward]

marco atzeri wrote:


Sent: Wednesday, March 23, 2011 12:36 PM
Subject: Re: cyggfortran-3.dll broken ?


[snip...]

So I caused myself the problem as I added all those functions to 
cygwin


But they were just in time to save me having to abandon my primary 
application on Cygwin.  Thank you.  Your efforts are appreciated.


Best regards,

-- Don W.

[snip...]


Regards
Marco



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gcc4: throwing exception from signal handler

[Don Ward]

I would like to be able to catch certain signals (SIGSEGV and SIGSYS) and 
throw a C++ exception (to be caught in a try/catch construct).  As a simple 
example:


#include stdio.h
#include string.h
#include stdexcept
#include signal.h
void throw_signal( int signum )
{
 // fprintf(stderr,throw_signal: before throw; 
signum=%d\n,signum);fflush(stderr);

 throw std::runtime_error (throw_signal);
}
int main() {
 struct sigaction new_action, d_old_action;
 memset (new_action, 0, sizeof (new_action));
 new_action.sa_handler = throw_signal;
 sigemptyset (new_action.sa_mask);
 new_action.sa_flags = 0;
 if (sigaction (SIGSEGV, new_action, d_old_action)  0){
   perror (sigaction (install new));
   throw std::runtime_error (sigaction);
 }
 try {
   int j = *((int *)NULL);
 }
 catch (...){
   printf(caught exception\n);
 }
}

g++ 3.3.4 gives the result I expect:

$ sh /usr/bin/set-gcc-default-3.sh
$ gcc --version
gcc (GCC) 3.4.4 (cygming special, gdc 0.12, using dmd 0.125)
Copyright (C) 2004 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
$ g++ -fnon-call-exceptions throw_segv.cc
$ ./a.exe
caught exception

but g++ 4.3.4 aborts after the exception is thrown and before it is caught:

$ sh /usr/bin/set-gcc-default-4.sh
$ gcc --version
gcc (GCC) 4.3.4 20090804 (release) 1
Copyright (C) 2008 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
$ g++ -fnon-call-exceptions throw_segv.cc
$ ./a.exe
terminate called after throwing an instance of 'std::runtime_error'
 what():  throw_signal
Aborted (core dumped)

Am I misunderstanding how this should work or doing something wrong?  Or is 
this a problem with Cygwin or gcc?


Thanks,

-- Don W.


cygcheck.out
Description: Binary data


throw_segv.cc
Description: Binary data
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Re: gcc4: throwing exception from signal handler

[Don Ward]

Václav Haismam wrote:


On Thu, 8 Jul 2010 09:01:41 -0400, Don Ward wrote:

I would like to be able to catch certain signals (SIGSEGV and SIGSYS)

and

throw a C++ exception (to be caught in a try/catch construct).  As a
simple
example:
[...]
Am I misunderstanding how this should work or doing something wrong?  Or
is
this a problem with Cygwin or gcc?

I do not think that handling SIGSEGV with an exception is a good idea.


I agree, in general.


Unless you get SIGSEGV as a result of some well thought through memory
management games


But that is what I am doing.  I also want to catch SIGSYS to determine 
whether shmat() is available when we don't know in advance whether cygserver 
is running.  In either case, if the signal is generated I want to catch it 
and try something else.  In these contexts I want to treat  SIGSEGV and 
SIGSYS as non-fatal error returns.


. . .

I am not sure but I do not think that throwing exceptions from signal
handlers is generally supported.


It appears that is what the -fnon-call-exceptions is for.  From the 
gcc-4.3.5 manual:


-fnon-call-exceptions:  Generate code that allows trapping instructions to 
throw exceptions. Note that this requires platform-specific runtime support 
that does not exist everywhere.


I guess one question is whether the runtime support exists in Cygwin 1.7 
with gcc 4.3.4.


-- Don W.


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Re: gcc4: throwing exception from signal handler

[Don Ward]

Dave Korn wrote:


On 08/07/2010 14:01, Don Ward wrote:

I would like to be able to catch certain signals (SIGSEGV and SIGSYS)
and throw a C++ exception (to be caught in a try/catch construct).  As a
simple example:



Am I misunderstanding how this should work or doing something wrong?  Or
is this a problem with Cygwin or gcc?


 Throwing exceptions from a signal handler is a can of worms that requires
support from both the compiler and the C runtime.


Understood!


 I was working on adding
this support for the distro package of gcc-4.5 before I had to go AWOL a
couple of weeks ago; it requires building the Cygwin DLL with EH tables, 
and

adding support in the last-chance stack unwinder in libgcc that is able to
unwind past our sigfe/sigbe stuff.


I'm glad someone is (or will be) working on it.  In the meanwhile, I can 
make do with gcc 3.4.4.


Thanks,

-- Don W.


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