Re: [PATCH 2/2 v2] Demangler crash handler

Gary Benson
2014-05-19T19:05:44Z

Eli Zaretskii wrote:
> > Date: Mon, 19 May 2014 16:48:23 +0100
> > From: Gary Benson <gbenson@redhat.com>
> > Cc: gdb-patches@sourceware.org, aburgess@broadcom.com, xdje42@gmail.com,
> > fw@deneb.enyo.de, mark.kettenis@xs4all.nl, palves@redhat.com,
> > tromey@redhat.com
> >
> > > Can't say this option makes sense to me. Isn't there a way to
> > > display the necessary information in a message, even though you
> > > catch the signal?
> >
> > To clarify, the current situation in GDB is that crashes in the
> > demangler are not caught:
> >
> > (gdb) set lang c++
> > (gdb) maint demangle _Z1-Av23*;cG~Wo2Vu
> > Segmentation fault (core dumped)
> >
> > With the patch, that is also the default situation. But with the
> > patch, with "maint set catch-demangler-crashes on", a signal
> > handler is installed across calls to the demangler, so that if the
> > demangler crashes you get something like this:
> >
> > (gdb) set lang c++
> > (gdb) maint set catch-demangler-crashes on
> > (gdb) maint demangle _Z1-Av23*;cG~Wo2Vu
> > /home/gary/work/archer/demangle-crashcatcher/src/gdb/cp-support.c:1590: internal-warning: unable to demangle '_Z1-Av23*;cG~Wo2Vu' (demangler failed with signal 11)
> > A problem internal to GDB has been detected,
> > further debugging may prove unreliable.
> > Quit this debugging session? (y or n) y
> >
> > /home/gary/work/archer/demangle-crashcatcher/src/gdb/cp-support.c:1590: internal-warning: unable to demangle '_Z1-Av23*;cG~Wo2Vu' (demangler failed with signal 11)
> > A problem internal to GDB has been detected,
> > further debugging may prove unreliable.
> > Create a core file of GDB? (y or n) y
> > Aborted (core dumped)
>
> Yes, I knew all that (because I've read all the deliberations here
> about this feature). I'm asking why do we need this option, instead
> of having its ON effect by default?

Ah, my apologies. On by default is my preference--it seems to work,
and it doesn't rob performance--but I don't think that will to be
accepted because there's no way to do this without (sig)longjmp, and
that isn't safe to call from a signal handler. A disabled-by-default
catcher is at least somewhat helpful in triaging all these demangler
bugs that are coming in now people are starting to use C++11 features.

> > --- a/gdb/doc/gdb.texinfo
> > +++ b/gdb/doc/gdb.texinfo
> > @@ -33142,6 +33142,16 @@ Expand symbol tables.
> > If @var{regexp} is specified, only expand symbol tables for file
> > names matching @var{regexp}.
> >
> > +@kindex maint set catch-demangler-crashes
> > +@kindex maint show catch-demangler-crashes
>
> Please add here
>
> @cindex demangler crashes
>
> Otherwise, this part is OK. Thanks.

Thank you.
Gary

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