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

[Andrew J. Schorr]

Another variant:

bash-4.2$ ./gawk 'function f(x) {return x} BEGIN {f(a["b"]); print 
typeof(a["b"])}'
gawk: cmd. line:1: fatal: typeof: invalid argument type `Node_var'

On Tue, Feb 21, 2023 at 09:55:40AM -0500, Andrew J. Schorr 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!
> 
> 
> On Mon, 2023-02-20 at 10:13 -0500, Andrew J. Schorr wrote:
> > Hi,
> > 
> > On Mon, Feb 20, 2023 at 02:43:58AM -0600, Daniel Pouzzner via 
> > Gawkextlib-users wrote:
> > > Is gawkextlib xml expected to work with gawk 5.2.1 (API 3.2), with the new
> > > AWK_BOOL?
> > 
> > I naively expect it to work. :-) If it doesn't work, then we've got a 
> > problem.
> > 
> > > It works as expected with awk 5.1.1, and with all earlier versions going 
> > > back to
> > > 4.1.3. I've been using it regularly since 2017.
> > 
> > Glad to hear you've been finding it useful.
> > 
> > > But with 5.2.1 I'm seeing anomalous behavior where empty xml elements 
> > > (e.g.
> > > <doi></doi>) are evaluating as true even though they string-equal "".
> > > 
> > > In connection with that empty xml field, gawk 5.2.1 crashes with
> > > 
> > > gawk: ../mkbib.awk:1142: (FILENAME=buzsaki_2003_EEG_source.xml FNR=173) 
> > > fatal: internal error: file eval.c, line 1358: unexpected parameter type 
> > > Node_illegal
> > > 
> > > If I build with sanitizer, I see concat_exp() doing a double-free of an 
> > > arg that
> > > was earlier freed by r_interpret().
> > > 
> > > I did a whole slew of experiments to try to understand what's happening, 
> > > but
> > > it's a large and tricky code base.  It seems to have something to do with
> > > Node_var appearing where usually Node_val is, but I was quickly in over 
> > > my head.
> > > 
> > > libgawkextlib and xml.so were both built with gawk-5.2.1 installed.  I 
> > > tried
> > > with old release code and with the latest git sources -- same result, as 
> > > above.
> > > 
> > > If it's useful I can share buzsaki_2003_EEG_source.xml and even the script
> > > that's crashing on 5.2.1.
> > 
> > Do you have a small test case that reproduces the problem? That would be 
> > very
> > helpful for debugging. If you don't have a small test case, then I guess a 
> > large
> > test case may be better than nothing.
> > 
> > Regards,
> > Andy
> 
> 
> 
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> 
> ----- End forwarded message -----

> 
>    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"];
>    }
> 


-- 
Andrew Schorr                      e-mail: aschorr@telemetry-investments.com
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