Re: Segfault upon exit when rxvt-unicode 9.22 is compiled against Perl 5.32
On Tue, Jun 30, 2020 at 10:46:54PM -0500, Rob Hoelz wrote: > That would work, but wouldn't that potentially break users' extensions by > getting rid > of global destruction time? For example, if a user did something like this: No, because a) perl doesn't guarantee calling destructors on process exit and b) perl corrupts data structures at this stage, so it's not a reliable mechanism in any case. (See e.g. http://blog.schmorp.de/2015-11-12-tidbits-why-coro-crashes-or-how-perl-6-deals-with-bugs.html). > ...the clean up code in the guard would never run, right? Yes, but IMnsHO that's better than if it were to run only sometimes, and lead to crashes at other times, but it all seemed to work during development. > Also, if any *other* library decided to call getenv in an exit handler, > the segfault would pop up again. The solution could be further optimised by calling _exit, leading to even faster exit times. > on the details of the copying and swapping of the environment that > rxvt-unicode does (I'm > guessing it has to do with urxvtd), but is there a way the code could be > modified to restore > environ to a valid pointer before main() returns? Possibly. But anything added makes things bigger and slower, and this must be offset by a tangible gain. -- The choice of a Deliantra, the free code+content MORPG -==- _GNU_ http://www.deliantra.net ==-- _ generation ---==---(_)__ __ __ Marc Lehmann --==---/ / _ \/ // /\ \/ / schm...@schmorp.de -=/_/_//_/\_,_/ /_/\_\ ___ rxvt-unicode mailing list rxvt-unicode@lists.schmorp.de http://lists.schmorp.de/mailman/listinfo/rxvt-unicode
Re: Segfault upon exit when rxvt-unicode 9.22 is compiled against Perl 5.32
On Tue, 30 Jun 2020 09:26:17 +0200
Marc Lehmann wrote:
> Hi, and thanks for your report!
>
> On Mon, Jun 29, 2020 at 07:40:41PM -0500, Rob Hoelz
> wrote:
> > I just upgraded my system (Arch Linux) to Perl 5.32, and I noticed
> > that urxvt started dropping core files upon exit. I dug into this,
> > and it seems that unlike Perl 5.30 or previous versions, Perl 5.32
> > unconditionally calls getenv("PERL_DESTRUCT_LEVEL") in
> > perl_destruct, which is called at atexit handler time. Because
> > rxvt_term makes a copy of the original process environment which it
> > assigns to environ, and then it frees that copy in its destructor
> > when ev_run is wrapping up, this results in a use-after-free when
> > perl_destruct is called, and occasionally a segfault.
> >
> > I patched my local rxvt-unicode package with a workaround - it just
> > sets environ = rxvt_environ after ev_run returns, but maybe a
> > better approach exists.
>
> Hmm, I think the altogether better solution is to simply get rid of
> ~rxvt_perl_interp. Does something like this also work for you?
>
>rxvt_perl_interp::~rxvt_perl_interp ()
>{
>}
>
> i.e. simply remove all code from ~rxvt_perl_interp.
>
> That's basically what I aim for in the next release.
>
That would work, but wouldn't that potentially break users' extensions by
getting rid
of global destruction time? For example, if a user did something like this:
use Guard;
our $g = guard {
# clean up
};
...the clean up code in the guard would never run, right? Also, if any *other*
library
decided to call getenv in an exit handler, the segfault would pop up again.
I'm not super clear
on the details of the copying and swapping of the environment that rxvt-unicode
does (I'm
guessing it has to do with urxvtd), but is there a way the code could be
modified to restore
environ to a valid pointer before main() returns?
-Rob
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Re: Segfault upon exit when rxvt-unicode 9.22 is compiled against Perl 5.32
Hi, and thanks for your report!
On Mon, Jun 29, 2020 at 07:40:41PM -0500, Rob Hoelz wrote:
> I just upgraded my system (Arch Linux) to Perl 5.32, and I noticed that urxvt
> started dropping core files upon exit. I dug into this, and it seems
> that unlike Perl 5.30 or previous versions, Perl 5.32 unconditionally calls
> getenv("PERL_DESTRUCT_LEVEL") in perl_destruct, which is called at
> atexit handler time. Because rxvt_term makes a copy of the original process
> environment which it assigns to environ, and then it frees that copy
> in its destructor when ev_run is wrapping up, this results in a
> use-after-free when perl_destruct is called, and occasionally a segfault.
>
> I patched my local rxvt-unicode package with a workaround - it just sets
> environ = rxvt_environ after ev_run returns, but maybe a better approach
> exists.
Hmm, I think the altogether better solution is to simply get rid of
~rxvt_perl_interp. Does something like this also work for you?
rxvt_perl_interp::~rxvt_perl_interp ()
{
}
i.e. simply remove all code from ~rxvt_perl_interp.
That's basically what I aim for in the next release.
--
The choice of a Deliantra, the free code+content MORPG
-==- _GNU_ http://www.deliantra.net
==-- _ generation
---==---(_)__ __ __ Marc Lehmann
--==---/ / _ \/ // /\ \/ / schm...@schmorp.de
-=/_/_//_/\_,_/ /_/\_\
___
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Segfault upon exit when rxvt-unicode 9.22 is compiled against Perl 5.32
Hello!
I just upgraded my system (Arch Linux) to Perl 5.32, and I noticed that urxvt
started dropping core files upon exit. I dug into this, and it seems
that unlike Perl 5.30 or previous versions, Perl 5.32 unconditionally calls
getenv("PERL_DESTRUCT_LEVEL") in perl_destruct, which is called at
atexit handler time. Because rxvt_term makes a copy of the original process
environment which it assigns to environ, and then it frees that copy
in its destructor when ev_run is wrapping up, this results in a use-after-free
when perl_destruct is called, and occasionally a segfault.
I patched my local rxvt-unicode package with a workaround - it just sets
environ = rxvt_environ after ev_run returns, but maybe a better approach
exists.
-Rob Hoelz
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