GNU bug report logs - #79483
Segmentation fault: set-car! in compiled code

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Владимир ВНИИАЭС
 <var-vniiaes <at> mail.ru>
To: bug-guile <at> gnu.org
Subject: Segmentation fault: set-car! in compiled code
Date: Mon, 22 Sep 2025 00:50:57 +0300

[Message part 1 (text/plain, inline)]

Hello,
 
Execution of   (set-car! '(0) 1)   *in compiled code*  leads to segfault:
 
amaya <at> AM4:~$ guile-3.0 --version
guile (GNU Guile) 3.0.10
Packaged by Debian (3.0.10+really3.0.10-4)
Copyright (C) 2024 Free Software Foundation, Inc.
 
License LGPLv3+: GNU LGPL 3 or later <http://gnu.org/licenses/lgpl.html>.
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.
 
amaya <at> AM4:~$ echo "(set-car! '(0) 1)" > /tmp/t.scm && guile /tmp/t.scm
;;; note: source file /tmp/t.scm
;;;       newer than compiled /home/amaya/.cache/guile/ccache/3.0-LE-8-4.7/tmp/t.scm.go
;;; note: auto-compilation is enabled, set GUILE_AUTO_COMPILE=0
;;;       or pass the --no-auto-compile argument to disable.
;;; compiling /tmp/t.scm
;;; compiled /home/amaya/.cache/guile/ccache/3.0-LE-8-4.7/tmp/t.scm.go
Segmentation fault (core dumped)
     
 
 
 

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Message #8 received at 79483 <at> debbugs.gnu.org (full text, mbox):

From: <tomas <at> tuxteam.de>
To: Владимир ВНИИАЭС
 <var-vniiaes <at> mail.ru>
Cc: 79483 <at> debbugs.gnu.org
Subject: Re: bug#79483: Segmentation fault: set-car! in compiled code
Date: Mon, 22 Sep 2025 06:35:18 +0200

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On Mon, Sep 22, 2025 at 12:50:57AM +0300, var-vniiaes--- via Bug reports for GUILE, GNU's Ubiquitous Extension Language wrote:
> 
> Hello,
>  
> Execution of   (set-car! '(0) 1)   *in compiled code*  leads to segfault:

First of all: you shouldn't be doing that :)

You are mutating a constant. I don't know what the Scheme specification says
to it (if at all).

The other question is whether Guile should/could catch that and signal an
error instead.

Cheers
-- 
t

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Message #11 received at 79483 <at> debbugs.gnu.org (full text, mbox):

From: Tomas Volf <~@wolfsden.cz>
To: <tomas <at> tuxteam.de>
Cc: Владимир ВНИИАЭС
 <var-vniiaes <at> mail.ru>, 79483 <at> debbugs.gnu.org
Subject: Re: bug#79483: Segmentation fault: set-car! in compiled code
Date: Mon, 22 Sep 2025 21:27:54 +0200

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<tomas <at> tuxteam.de> writes:

> On Mon, Sep 22, 2025 at 12:50:57AM +0300, var-vniiaes--- via Bug reports for GUILE, GNU's Ubiquitous Extension Language wrote:
>> 
>> Hello,
>>  
>> Execution of   (set-car! '(0) 1)   *in compiled code*  leads to segfault:
>
> First of all: you shouldn't be doing that :)
>
> You are mutating a constant. I don't know what the Scheme specification says
> to it (if at all).

--8<---------------cut here---------------start------------->8---
As noted in section 3.4, it is an error to attempt to alter
a constant (i.e. the value of a literal expression) using a
mutation procedure like set-car! or string-set!
--8<---------------cut here---------------end--------------->8---

> The other question is whether Guile should/could catch that and signal an
> error instead.

I believe it should not.  Memory-safe languages (and, Guile is supposed
to be one) should never segfault but instead terminate with a sensible
error.  I realize that 1.3.2 allows to "fail catastrophically", which
segfault probably qualifies as, but I believe we should do better.

Tomas

-- 
There are only two hard things in Computer Science:
cache invalidation, naming things and off-by-one errors.

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Message #14 received at 79483 <at> debbugs.gnu.org (full text, mbox):

From: tomas <at> tuxteam.de
To: Tomas Volf <~@wolfsden.cz>
Cc: Владимир ВНИИАЭС
 <var-vniiaes <at> mail.ru>, 79483 <at> debbugs.gnu.org
Subject: Re: bug#79483: Segmentation fault: set-car! in compiled code
Date: Tue, 23 Sep 2025 06:22:45 +0200

[Message part 1 (text/plain, inline)]

On Mon, Sep 22, 2025 at 09:27:54PM +0200, Tomas Volf wrote:
> <tomas <at> tuxteam.de> writes:
> 
> > On Mon, Sep 22, 2025 at 12:50:57AM +0300, var-vniiaes--- via Bug reports for GUILE, GNU's Ubiquitous Extension Language wrote:
> >> 
> >> Hello,
> >>  
> >> Execution of   (set-car! '(0) 1)   *in compiled code*  leads to segfault:
> >
> > First of all: you shouldn't be doing that :)
> >
> > You are mutating a constant. I don't know what the Scheme specification says
> > to it (if at all).
> 
> --8<---------------cut here---------------start------------->8---
> As noted in section 3.4, it is an error to attempt to alter
> a constant (i.e. the value of a literal expression) using a
> mutation procedure like set-car! or string-set!
> --8<---------------cut here---------------end--------------->8---
> 
> > The other question is whether Guile should/could catch that and signal an
> > error instead.
> 
> I believe it should not.

This is ambiguous, but from the context below I think you mean Guile
should catch it. I agree :-)

> Memory-safe languages (and, Guile is supposed
> to be one) should never segfault but instead terminate with a sensible
> error.  I realize that 1.3.2 allows to "fail catastrophically", which
> segfault probably qualifies as, but I believe we should do better.

Definitely -- the question is whether Guile wants to rely on the
OS/runtime to catch an out-of-bounds access (or more probably here
an access to a region marked read-onls) or catch it itself.

Cheers
-- 
tomás

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