GNU bug report logs - #79360
30.2; lldb shows incorrect code location when no column number is available

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

From: Gustav Hållberg <gustav <at> gmail.com>
To: bug-gnu-emacs <at> gnu.org
Subject: 30.2;
 lldb shows incorrect code location when no column number is available
Date: Mon, 1 Sep 2025 16:42:33 +0200

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

In (lldb), there is a bug that positions the source code location on the
last character of the previous line if lldb doesn't report a column number.

Example, save the following as "t.s" and compile (on x86-64) with "gcc -g
t.s -o t":

        .global _main
_main:
        xor %eax,%eax
        ret

and debug using (lldb "lldb ./t"):

(lldb) *b main*
  :
(lldb) *run*
  :
(lldb)
*disas*t`main:
    0x555555555129 <+0>: xorl   %eax, %eax
->  0x55555555512b <+2>: retq

but the source code location ends up at the last character of the "xor
%eax..." line.

Attaching proposed pach against 66ef930ebea4618c1dac71a09495766476ced1d6.

[Message part 2 (text/html, inline)]

[0001-lldb-bugfix-source-code-location-without-column.patch (application/octet-stream, attachment)]

Message #8 received at 79360 <at> debbugs.gnu.org (full text, mbox):

From: Eli Zaretskii <eliz <at> gnu.org>
To: Gustav Hållberg <gustav <at> gmail.com>
Cc: 79360 <at> debbugs.gnu.org
Subject: Re: bug#79360: 30.2;
 lldb shows incorrect code location when no column number is available
Date: Mon, 01 Sep 2025 18:52:26 +0300

> From: Gustav Hållberg <gustav <at> gmail.com>
> Date: Mon, 1 Sep 2025 16:42:33 +0200
> 
> In (lldb), there is a bug that positions the source code location on the last character of the previous line if
> lldb doesn't report a column number.
> 
> Example, save the following as "t.s" and compile (on x86-64) with "gcc -g t.s -o t":
> 
>         .global _main
> _main:
>         xor %eax,%eax
>         ret
> 
> and debug using (lldb "lldb ./t"):
> 
> (lldb) b main
>   :
> (lldb) run
>   :
> (lldb) disas
> t`main:
>     0x555555555129 <+0>: xorl   %eax, %eax
> ->  0x55555555512b <+2>: retq
> 
> but the source code location ends up at the last character of the "xor %eax..." line.
> 
> Attaching proposed pach against 66ef930ebea4618c1dac71a09495766476ced1d6.

Thanks, but if this is a bug in lldb, why shouldn't it be solved in
lldb, not in Emacs?

Message #11 received at 79360 <at> debbugs.gnu.org (full text, mbox):

From: Gustav Hållberg <gustav <at> gmail.com>
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: 79360 <at> debbugs.gnu.org
Subject: Re: bug#79360: 30.2; lldb shows incorrect code location when no
 column number is available
Date: Mon, 1 Sep 2025 19:09:10 +0200

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

It is a bug in the emacs M-x lldb command.

lldb (the tool) correctly sends an empty column field when it has no column
number debug information.

If you look at the patch you'll see that the gud.el regexp (correctly)
matches an empty digit sequence for the column number field, but that
(incorrectly) is treated as column zero (which doesn't exist) rather than
an absent column number field.

On Mon, Sep 1, 2025 at 5:52 PM Eli Zaretskii <eliz <at> gnu.org> wrote:

> > From: Gustav Hållberg <gustav <at> gmail.com>
> > Date: Mon, 1 Sep 2025 16:42:33 +0200
> >
> > In (lldb), there is a bug that positions the source code location on the
> last character of the previous line if
> > lldb doesn't report a column number.
> >
> > Example, save the following as "t.s" and compile (on x86-64) with "gcc
> -g t.s -o t":
> >
> >         .global _main
> > _main:
> >         xor %eax,%eax
> >         ret
> >
> > and debug using (lldb "lldb ./t"):
> >
> > (lldb) b main
> >   :
> > (lldb) run
> >   :
> > (lldb) disas
> > t`main:
> >     0x555555555129 <+0>: xorl   %eax, %eax
> > ->  0x55555555512b <+2>: retq
> >
> > but the source code location ends up at the last character of the "xor
> %eax..." line.
> >
> > Attaching proposed pach against 66ef930ebea4618c1dac71a09495766476ced1d6.
>
> Thanks, but if this is a bug in lldb, why shouldn't it be solved in
> lldb, not in Emacs?
>

[Message part 2 (text/html, inline)]

Message #16 received at 79360-done <at> debbugs.gnu.org (full text, mbox):

From: Eli Zaretskii <eliz <at> gnu.org>
To: Gustav Hållberg <gustav <at> gmail.com>
Cc: 79360-done <at> debbugs.gnu.org
Subject: Re: bug#79360: 30.2; lldb shows incorrect code location when no
 column number is available
Date: Sat, 06 Sep 2025 12:06:14 +0300

> From: Gustav Hållberg <gustav <at> gmail.com>
> Date: Mon, 1 Sep 2025 19:09:10 +0200
> Cc: 79360 <at> debbugs.gnu.org
> 
> It is a bug in the emacs M-x lldb command.
> 
> lldb (the tool) correctly sends an empty column field when it has no column number debug information.
> 
> If you look at the patch you'll see that the gud.el regexp (correctly) matches an empty digit sequence for the
> column number field, but that (incorrectly) is treated as column zero (which doesn't exist) rather than an
> absent column number field.

Thanks, I've now installed the change on the master branch, and I'm
therefore closing this bug.

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