Re: [Gcl-devel] Re: gcl_signal

[Camm Maguire]

Greetings!

"Mike Thomas" <address@hidden> writes:

> Hi Camm.
> 
> | > In HEAD I increased the declaration size to 32 to cover the max
> | number of signals.  I also added a definition of
> | > INSTALL_SEGMENTATION_CATCHER to mingw.h to address the problem
> | of an immediate exit from GCL whenever a seg fault
> | > occurred on Windows.  This allows examination of the Lisp
> | environment from the Lisp debugger after a seg fault, so for
> | > example, the gcc 3.3.3 crash at specfn.o load in the Maxima
> | build is reported as appended below.  The down side is that
> | > it stops the problem from dumping out to the C debugger - ie
> | for that you need to rebuild without the handler.
> | >
> |
> | Is this perhaps due to the way mingw 'fakes' unix signals?
> 
> For clarity - it is actually the Microsoft Visual C runtime library
> (MSVCRT.DLL, a part of all modern Windows systems) which does this.  MinGW32
> just hooks up to that library with a thin covering layer and a few minor
> additions - hence it's name "Minimalist GCC for Windows 32".  Whether that
> layer affects the discussion below I don't yet know.
> 
> Unfortunately I don't know how the MSVCRT implements signals - they are not
> part of the OS as such.  If we were doing the job properly, we would at
> least consider replacing the entire GCL signal system on Windows but I
> haven't thought of a good way to do this as I don't really understand the
> signal system to start with.  As an example of the kind of issues involved,
> see:
> 
> http://archives.postgresql.org/pgsql-hackers-win32/2003-10/msg00022.php
> 
>   and
> 
> http://msdn.microsoft.com/library/default.asp?url=/library/en-us/vccore98/ht
> ml/_crt_signal.asp
> 
> which lists the kind of functions which it is safe to call in a signal
> handler - it seems not very many at all.
> 
> Add to this the fact that set/longjump doesn't preserve register variables
> (I believe that most modern compilers ignore the register modifier anyway)
> and it is hard to work out what is best, and more importantly, what is
> mumbo-jumbo.
> 
> 
> 
> | My gdb
> | will first stop at the sigsegv, then proceed to the handler when I
> | continue.  In any case, I think you can break at error and still get a
> | stack trace across the signal handler to the location of the fault.
> 
> I'll try this at some stage.  I was referring to running GCL without the
> debugger.  When GCL intercepts the segmentation "signal", it doe not fall
> through to the OS default debugger.
> 
> | Just wondering if this is helping in any of the known problem areas.
> 
> No, yes and no.
> 
> I went through the signal code in the hope of finding a miracle cure and
> failed, but on the other hand it has provided a neater way to get at the
> Lisp side point of failure than print debugging, but no, it has not yet
> helped my attempts to sort out an Axiom problem in similar vein.
> 
> I am chasing the gcc 3.3.3/3.4.0 Maxima specfn crash which I have so far
> traced through from the C side as far as the execution of _init_specfn in
> fasload() and on a much earlier occasion in the array initialisation code,
> and the LISP side using both the above mentioned Lisp debugger back trace
> and Lisp style print debugging.  The question is why the array
> initialisation causes a segfault.
> 

Just a note here that I'd try (setq si::*notify-gbc* t) and if
promising, break at GBC in gdb and look at a backtrace.

> My next steps will be to look at the C code being generated and also
> possibly to produce a minimal lisp file which can be loaded without the
> entire Maxima infrastructure coming in - I got stuck on how to get *ARRAY
> defined on the weekend.
> 
> I also intend tracing further with the debugger the array "cursor"
> initialisation which I have found to be particularly difficult to understand
> during previous attempts.
> 

Thanks as always for your efforts!

> Cheers
> 
> Mike Thomas.
> 
> 
> 
> 
> 

-- 
Camm Maguire                                            address@hidden
==========================================================================
"The earth is but one country, and mankind its citizens."  --  Baha'u'llah