GNU bug report logs - #50268
28.0.50; Assertion warning during native compilation

Previous Next

Full log

View this message in rfc822 format

From: Andrea Corallo <akrl <at> sdf.org>
To: 50268 <at> debbugs.gnu.org
Cc: mwd <at> md5i.com, monnier <at> iro.umontreal.ca
Subject: bug#50268: 28.0.50; Assertion warning during native compilation
Date: Tue, 21 Sep 2021 07:50:35 +0000

Andrea Corallo via "Bug reports for GNU Emacs, the Swiss army knife of
text editors" <bug-gnu-emacs <at> gnu.org> writes:

> Michael Welsh Duggan <mwd <at> md5i.com> writes:
>
>> I was able to determine that there was a bug in the pacproxy.el code
>> that I included in the bug report.  Fixing that bug caused native
>> compilation to work.  The assertion and backtrace were not particularly
>> useful in determining the bug in the code, though.  The bug was in the
>> `pacproxy--retrieve-wpad' function when I let-bound the following
>> illegal lambda:
>>
>>   (lambda (&rest) "DIRECT")
>>
>> The fix was to change this to:
>>
>>   (lambda (&rest _) "DIRECT")
>>
>> Is there another part of the compiler that could have caught this and
>> returned a useful diagnostic?
>
> Hi Michael & all,
>
> I had a quick look and these are my findings:
>
> (byte-compile '(lambda (&rest _) "DIRECT"))
> =>
> #[128 "\300\207" ["DIRECT"] 2 "DIRECT
>
> (fn &rest _)"]
>
> Here we have as encoded signature 128 (one rest arg) and the frame size
> is 2 (one for the rest arg and one for the immediate). Fine...
>
> (byte-compile '(lambda () "DIRECT"))
> =>
> #[0 "\300\207" ["DIRECT"] 1 "DIRECT"] 
>
> Here we have as encoded signature 0 (no args) and the frame size is 1
> (will be used by the immediate).  Fine as well.
>
> (byte-compile '(lambda (&rest) "DIRECT"))
> =>
> #[128 "\300\207" ["DIRECT"] 1 "DIRECT
>
> (fn &rest)"]
>
> This is the problematic case that was signaled as reproducer.  Here we
> have as encoded signature 128 (one rest arg) but the frame size (1) is
> not accounting for this.
>
> I think this output is a incoherent and I guess the byte compiler should
> probably just raise an error and refuse to compile if the lambda list is
> invalid.  Am I wrong?

I can't verify in this moment but I guess is very possible we even
overflow in the byte interpreter when executing the mentioned bytecode.

  Andrea

Previous Next

GNU bug tracking system
Copyright (C) 1999 Darren O. Benham, 1997,2003 nCipher Corporation Ltd, 1994-97 Ian Jackson.