Re: fixtype: Assertion `n->type == Node_val' failed

[arnold]

Please try building from git, gawk-5.2-stable branch.

I never saw a double-free error; what system is this happening on?
Can you run valgrind --leak-check=full on it as well?

Thanks,

Arnold

Daniel Pouzzner <douzzer@mega.nu> wrote:

> The patch is progress:
>
>    $ /tmp/portage/sys-apps/gawk-5.2.1/image/usr/bin/gawk -f /tmp/arraybug.awk 
>    a[b] is false
>    a[b] is false
>    free(): double free detected in tcache 2
>    Aborted
>    
>
> On Thu, 2023-02-23 at 10:59 -0700, arnold@skeeve.com wrote:
> > Hi.
> > 
> > Thanks for the report. Please see the patch below.
> > 
> > Arnold
> > 
> > "Andrew J. Schorr" <aschorr@telemetry-investments.com> wrote:
> > 
> > > Hi,
> > > 
> > > Please see the attached bug reproducer discovered by
> > > Daniel Pouzzner. Thanks to Daniel for finding this.
> > > When run against the master branch, I see this:
> > > 
> > > bash-4.2$ ./gawk -f /tmp/bug.awk
> > > a[b] is false
> > > gawk: awk.h:2016: fixtype: Assertion `n->type == Node_val' failed.
> > > Aborted (core dumped)
> > > 
> > > Regards,
> > > Andy
> > > 
> > > ----- Forwarded message from Daniel Pouzzner via Gawkextlib-users 
> > > <gawkextlib-users@lists.sourceforge.net> -----
> > > 
> > > Date: Mon, 20 Feb 2023 15:37:56 -0600
> > > From: Daniel Pouzzner via Gawkextlib-users 
> > > <gawkextlib-users@lists.sourceforge.net>
> > > To: "Andrew J. Schorr" <aschorr@telemetry-investments.com>, 
> > > gawkextlib-users
> > >   <gawkextlib-users@lists.sourceforge.net>
> > > Cc: Daniel Pouzzner <douzzer@mega.nu>
> > > Subject: Re: [Gawkextlib-users] gawkextlib xml on gawk-5.2.1
> > > 
> > > I was able to whittle away the xml parts of the logic until none was 
> > > left.  This
> > > turns out to be a gawk core bug.  Reproducer:
> > > 
> > >    #!/usr/bin/gawk -f
> > >    
> > >    function f(x) {
> > >        return x;
> > >    }
> > >    
> > >    BEGIN {
> > >        print "a[b] is " (a["b"] ? "true" : "false");
> > > 
> > >        f(a["b"]);
> > > 
> > >        print "a[b] is " (a["b"] ? "true" : "false");
> > >    
> > >        print a["b"];
> > >    }
> > >    
> > > Result on 5.1.1:
> > > 
> > >    $ /tmp/arraybug.awk
> > >    a[b] is false
> > >    a[b] is false
> > >    
> > > On 5.2.1:
> > > 
> > >    $ /tmp/portage/sys-apps/gawk-5.2.1/image/usr/bin/gawk -f 
> > > /tmp/arraybug.awk
> > >    a[b] is false
> > >    a[b] is true
> > >    free(): double free detected in tcache 2
> > >    Aborted
> > >    
> > > 
> > > The syndrome in a nutshell: if a nonexistent array element is passed as an
> > > argument to a function, the element is sortof-created, such that testing 
> > > it
> > > somehow evaluates to true, but its state/internal pointers are invalid.  
> > > I've
> > > actually gotten scripts to outright SEGV and exhibit various other 
> > > obviously
> > > undefined behavior, like printing characters from the name of the redirect
> > > target ("/dev/stde" etc), by just changing the length of words in a printf
> > > format (constant string).
> > > 
> > > 
> > > Do I need to refile a bug on gawk core, or have I "done enough", as it 
> > > were?
> > > 
> > > 
> > > Oh and thanks for the quick turnaround!
> > ---------------------------------
> > diff --git a/awk.h b/awk.h
> > index 79cdd85..f6d0f99 100644
> > --- a/awk.h
> > +++ b/awk.h
> > @@ -2031,6 +2031,9 @@ fixtype(NODE *n)
> >  static inline bool
> >  boolval(NODE *t)
> >  {
> > +   if (t->type == Node_var)        // could have come from converted 
> > Node_elem_new
> > +           t = t->var_value;
> > +
> >     (void) fixtype(t);
> >     if ((t->flags & NUMBER) != 0)
> >             return ! is_zero(t);
>