Default debug format for AVR

Default debug format for AVR

[Simon Marchi]

Hi,

The default debug format (when using only -g) for the AVR target is
stabs.  Is there a reason for it not being DWARF, and would it be
possible to maybe consider possibly thinking about making it default to
DWARF?  I am asking because the support for stabs in GDB is pretty much
untested and bit-rotting, so I think it would be more useful for
everyone to use DWARF.

Simon

Re: Default debug format for AVR

[Jim Wilson]

On Sat, Apr 3, 2021 at 6:24 PM Simon Marchi via Gcc <gcc@gcc.gnu.org> wrote:

> The default debug format (when using only -g) for the AVR target is
> stabs.  Is there a reason for it not being DWARF, and would it be
> possible to maybe consider possibly thinking about making it default to
> DWARF?  I am asking because the support for stabs in GDB is pretty much
> untested and bit-rotting, so I think it would be more useful for
> everyone to use DWARF.
>

I tried to deprecate the stabs support a little over 4 years ago.
    https://gcc.gnu.org/pipermail/gcc-patches/2017-December/489296.html
There was a suggestion to change the error to a warning, but my startup
company job kept me so busy I never had a chance to follow up on this.

I would like to see the stabs support deprecated and the later removed from
gcc.  No new features have been added in a long time, and it is only being
maintained in the sense that when it fails it is fixed to ignore source
code constructs that it doesn't support.  The longer it survives in this
state, the less useful it becomes.

Jim

Re: Default debug format for AVR

[Simon Marchi]

On 2021-04-05 3:36 p.m., Jim Wilson wrote:> On Sat, Apr 3, 2021 at 6:24 PM Simon Marchi via Gcc <gcc@gcc.gnu.org <mailto:gcc@gcc.gnu.org>> wrote:
> 
>     The default debug format (when using only -g) for the AVR target is
>     stabs.  Is there a reason for it not being DWARF, and would it be
>     possible to maybe consider possibly thinking about making it default to
>     DWARF?  I am asking because the support for stabs in GDB is pretty much
>     untested and bit-rotting, so I think it would be more useful for
>     everyone to use DWARF.
> 
> 
> I tried to deprecate the stabs support a little over 4 years ago.
>     https://gcc.gnu.org/pipermail/gcc-patches/2017-December/489296.html <https://gcc.gnu.org/pipermail/gcc-patches/2017-December/489296.html>
> There was a suggestion to change the error to a warning, but my startup company job kept me so busy I never had a chance to follow up on this.
> 
> I would like to see the stabs support deprecated and the later removed from gcc.  No new features have been added in a long time, and it is only being maintained in the sense that when it fails it is fixed to ignore source code constructs that it doesn't support.  The longer it survives in this state, the less useful it becomes.
> 
> Jim

You have 100% my suppose on this.  The longer stabs survives (especially
as the default for an arch), the longer some people who don't know the
intricacies of debug formats could use it without knowing, and that
does them a disservice.

Simon

Re: Default debug format for AVR

[Richard Biener]

On Mon, Apr 5, 2021 at 10:56 PM Simon Marchi via Gcc <gcc@gcc.gnu.org> wrote:
>
> On 2021-04-05 3:36 p.m., Jim Wilson wrote:> On Sat, Apr 3, 2021 at 6:24 PM Simon Marchi via Gcc <gcc@gcc.gnu.org <mailto:gcc@gcc.gnu.org>> wrote:
> >
> >     The default debug format (when using only -g) for the AVR target is
> >     stabs.  Is there a reason for it not being DWARF, and would it be
> >     possible to maybe consider possibly thinking about making it default to
> >     DWARF?  I am asking because the support for stabs in GDB is pretty much
> >     untested and bit-rotting, so I think it would be more useful for
> >     everyone to use DWARF.
> >
> >
> > I tried to deprecate the stabs support a little over 4 years ago.
> >     https://gcc.gnu.org/pipermail/gcc-patches/2017-December/489296.html <https://gcc.gnu.org/pipermail/gcc-patches/2017-December/489296.html>
> > There was a suggestion to change the error to a warning, but my startup company job kept me so busy I never had a chance to follow up on this.
> >
> > I would like to see the stabs support deprecated and the later removed from gcc.  No new features have been added in a long time, and it is only being maintained in the sense that when it fails it is fixed to ignore source code constructs that it doesn't support.  The longer it survives in this state, the less useful it becomes.
> >
> > Jim
>
> You have 100% my suppose on this.  The longer stabs survives (especially
> as the default for an arch), the longer some people who don't know the
> intricacies of debug formats could use it without knowing, and that
> does them a disservice.

Patches to kill STABS (and related/derived formats) are pre-approved for stage1.

Richard.

> Simon

Re: Default debug format for AVR

[David Edelsohn]

On Tue, Apr 6, 2021 at 6:34 AM Richard Biener via Gcc <gcc@gcc.gnu.org> wrote:
>
> On Mon, Apr 5, 2021 at 10:56 PM Simon Marchi via Gcc <gcc@gcc.gnu.org> wrote:
> >
> > On 2021-04-05 3:36 p.m., Jim Wilson wrote:> On Sat, Apr 3, 2021 at 6:24 PM Simon Marchi via Gcc <gcc@gcc.gnu.org <mailto:gcc@gcc.gnu.org>> wrote:
> > >
> > >     The default debug format (when using only -g) for the AVR target is
> > >     stabs.  Is there a reason for it not being DWARF, and would it be
> > >     possible to maybe consider possibly thinking about making it default to
> > >     DWARF?  I am asking because the support for stabs in GDB is pretty much
> > >     untested and bit-rotting, so I think it would be more useful for
> > >     everyone to use DWARF.
> > >
> > >
> > > I tried to deprecate the stabs support a little over 4 years ago.
> > >     https://gcc.gnu.org/pipermail/gcc-patches/2017-December/489296.html <https://gcc.gnu.org/pipermail/gcc-patches/2017-December/489296.html>
> > > There was a suggestion to change the error to a warning, but my startup company job kept me so busy I never had a chance to follow up on this.
> > >
> > > I would like to see the stabs support deprecated and the later removed from gcc.  No new features have been added in a long time, and it is only being maintained in the sense that when it fails it is fixed to ignore source code constructs that it doesn't support.  The longer it survives in this state, the less useful it becomes.
> > >
> > > Jim
> >
> > You have 100% my suppose on this.  The longer stabs survives (especially
> > as the default for an arch), the longer some people who don't know the
> > intricacies of debug formats could use it without knowing, and that
> > does them a disservice.
>
> Patches to kill STABS (and related/derived formats) are pre-approved for stage1.

AIX continues to use and support STABS, although it is transitioning
to DWARF.  If this is intended as a general statement about removal of
STABS support in GCC, it is premature.

Thanks, David

Re: Default debug format for AVR

[Richard Biener]

On April 8, 2021 1:17:53 AM GMT+02:00, David Edelsohn <dje.gcc@gmail.com> wrote:
>On Tue, Apr 6, 2021 at 6:34 AM Richard Biener via Gcc <gcc@gcc.gnu.org>
>wrote:
>>
>> On Mon, Apr 5, 2021 at 10:56 PM Simon Marchi via Gcc
><gcc@gcc.gnu.org> wrote:
>> >
>> > On 2021-04-05 3:36 p.m., Jim Wilson wrote:> On Sat, Apr 3, 2021 at
>6:24 PM Simon Marchi via Gcc <gcc@gcc.gnu.org <mailto:gcc@gcc.gnu.org>>
>wrote:
>> > >
>> > >     The default debug format (when using only -g) for the AVR
>target is
>> > >     stabs.  Is there a reason for it not being DWARF, and would
>it be
>> > >     possible to maybe consider possibly thinking about making it
>default to
>> > >     DWARF?  I am asking because the support for stabs in GDB is
>pretty much
>> > >     untested and bit-rotting, so I think it would be more useful
>for
>> > >     everyone to use DWARF.
>> > >
>> > >
>> > > I tried to deprecate the stabs support a little over 4 years ago.
>> > >    
>https://gcc.gnu.org/pipermail/gcc-patches/2017-December/489296.html
><https://gcc.gnu.org/pipermail/gcc-patches/2017-December/489296.html>
>> > > There was a suggestion to change the error to a warning, but my
>startup company job kept me so busy I never had a chance to follow up
>on this.
>> > >
>> > > I would like to see the stabs support deprecated and the later
>removed from gcc.  No new features have been added in a long time, and
>it is only being maintained in the sense that when it fails it is fixed
>to ignore source code constructs that it doesn't support.  The longer
>it survives in this state, the less useful it becomes.
>> > >
>> > > Jim
>> >
>> > You have 100% my suppose on this.  The longer stabs survives
>(especially
>> > as the default for an arch), the longer some people who don't know
>the
>> > intricacies of debug formats could use it without knowing, and that
>> > does them a disservice.
>>
>> Patches to kill STABS (and related/derived formats) are pre-approved
>for stage1.
>
>AIX continues to use and support STABS, although it is transitioning
>to DWARF.  If this is intended as a general statement about removal of
>STABS support in GCC, 

Yes, it is. 

Richard.

it is premature.
>
>Thanks, David

Re: Default debug format for AVR

[David Edelsohn]

On Thu, Apr 8, 2021 at 2:03 AM Richard Biener
<richard.guenther@gmail.com> wrote:
>
> On April 8, 2021 1:17:53 AM GMT+02:00, David Edelsohn <dje.gcc@gmail.com> wrote:
> >On Tue, Apr 6, 2021 at 6:34 AM Richard Biener via Gcc <gcc@gcc.gnu.org>
> >wrote:
> >>
> >> On Mon, Apr 5, 2021 at 10:56 PM Simon Marchi via Gcc
> ><gcc@gcc.gnu.org> wrote:
> >> >
> >> > On 2021-04-05 3:36 p.m., Jim Wilson wrote:> On Sat, Apr 3, 2021 at
> >6:24 PM Simon Marchi via Gcc <gcc@gcc.gnu.org <mailto:gcc@gcc.gnu.org>>
> >wrote:
> >> > >
> >> > >     The default debug format (when using only -g) for the AVR
> >target is
> >> > >     stabs.  Is there a reason for it not being DWARF, and would
> >it be
> >> > >     possible to maybe consider possibly thinking about making it
> >default to
> >> > >     DWARF?  I am asking because the support for stabs in GDB is
> >pretty much
> >> > >     untested and bit-rotting, so I think it would be more useful
> >for
> >> > >     everyone to use DWARF.
> >> > >
> >> > >
> >> > > I tried to deprecate the stabs support a little over 4 years ago.
> >> > >
> >https://gcc.gnu.org/pipermail/gcc-patches/2017-December/489296.html
> ><https://gcc.gnu.org/pipermail/gcc-patches/2017-December/489296.html>
> >> > > There was a suggestion to change the error to a warning, but my
> >startup company job kept me so busy I never had a chance to follow up
> >on this.
> >> > >
> >> > > I would like to see the stabs support deprecated and the later
> >removed from gcc.  No new features have been added in a long time, and
> >it is only being maintained in the sense that when it fails it is fixed
> >to ignore source code constructs that it doesn't support.  The longer
> >it survives in this state, the less useful it becomes.
> >> > >
> >> > > Jim
> >> >
> >> > You have 100% my suppose on this.  The longer stabs survives
> >(especially
> >> > as the default for an arch), the longer some people who don't know
> >the
> >> > intricacies of debug formats could use it without knowing, and that
> >> > does them a disservice.
> >>
> >> Patches to kill STABS (and related/derived formats) are pre-approved
> >for stage1.
> >
> >AIX continues to use and support STABS, although it is transitioning
> >to DWARF.  If this is intended as a general statement about removal of
> >STABS support in GCC,
>
> Yes, it is.
>
> Richard.

Richard,

It is inappropriate to unilaterally make this decision without
discussion with all affected ports and maintainers, without warning,
and without deprecation.  I request that you rescind this decision.

It is somewhat ironic to act as a dictator when we are having a
discussion about dictatorial behavior in GCC leadership.

Thanks, David

Re: Default debug format for AVR

[Richard Biener]

On Thu, Apr 8, 2021 at 8:03 AM Richard Biener
<richard.guenther@gmail.com> wrote:
>
> On April 8, 2021 1:17:53 AM GMT+02:00, David Edelsohn <dje.gcc@gmail.com> wrote:
> >On Tue, Apr 6, 2021 at 6:34 AM Richard Biener via Gcc <gcc@gcc.gnu.org>
> >wrote:
> >>
> >> On Mon, Apr 5, 2021 at 10:56 PM Simon Marchi via Gcc
> ><gcc@gcc.gnu.org> wrote:
> >> >
> >> > On 2021-04-05 3:36 p.m., Jim Wilson wrote:> On Sat, Apr 3, 2021 at
> >6:24 PM Simon Marchi via Gcc <gcc@gcc.gnu.org <mailto:gcc@gcc.gnu.org>>
> >wrote:
> >> > >
> >> > >     The default debug format (when using only -g) for the AVR
> >target is
> >> > >     stabs.  Is there a reason for it not being DWARF, and would
> >it be
> >> > >     possible to maybe consider possibly thinking about making it
> >default to
> >> > >     DWARF?  I am asking because the support for stabs in GDB is
> >pretty much
> >> > >     untested and bit-rotting, so I think it would be more useful
> >for
> >> > >     everyone to use DWARF.
> >> > >
> >> > >
> >> > > I tried to deprecate the stabs support a little over 4 years ago.
> >> > >
> >https://gcc.gnu.org/pipermail/gcc-patches/2017-December/489296.html
> ><https://gcc.gnu.org/pipermail/gcc-patches/2017-December/489296.html>
> >> > > There was a suggestion to change the error to a warning, but my
> >startup company job kept me so busy I never had a chance to follow up
> >on this.
> >> > >
> >> > > I would like to see the stabs support deprecated and the later
> >removed from gcc.  No new features have been added in a long time, and
> >it is only being maintained in the sense that when it fails it is fixed
> >to ignore source code constructs that it doesn't support.  The longer
> >it survives in this state, the less useful it becomes.
> >> > >
> >> > > Jim
> >> >
> >> > You have 100% my suppose on this.  The longer stabs survives
> >(especially
> >> > as the default for an arch), the longer some people who don't know
> >the
> >> > intricacies of debug formats could use it without knowing, and that
> >> > does them a disservice.
> >>
> >> Patches to kill STABS (and related/derived formats) are pre-approved
> >for stage1.
> >
> >AIX continues to use and support STABS, although it is transitioning
> >to DWARF.  If this is intended as a general statement about removal of
> >STABS support in GCC,
>
> Yes, it is.

To clarify any such patches of course have to keep existing ports
working with at least one supported debug info format.  But I think
it's time to default to DWARF for ports that have the choice and in
turn disable the possibility to enable STABS on them (maybe with
a deprecation warning for one major release).

That includes keeping AIX working (there's AIX machines on
the compile-farm that can be used for testing).

That includes disabling / diagnosting deprecated -gstabs on
*-linux targets and switching AVR to dwarf [only] as was the
original request.

Richard.

Re: Default debug format for AVR

[Simon Marchi]

On 2021-04-08 9:11 a.m., David Edelsohn wrote:
>>> AIX continues to use and support STABS, although it is transitioning
>>> to DWARF.  If this is intended as a general statement about removal of
>>> STABS support in GCC,
>>
>> Yes, it is.
>>
>> Richard.
> 
> Richard,
> 
> It is inappropriate to unilaterally make this decision without
> discussion with all affected ports and maintainers, without warning,
> and without deprecation.  I request that you rescind this decision.
> 
> It is somewhat ironic to act as a dictator when we are having a
> discussion about dictatorial behavior in GCC leadership.

I don't really want to start such a debate about GCC politics.  If stabs
is not ready to be deleted, that's fine.  But it would be good to go
through all targets for which it is the default (like avr), and see if
they are ready to be switched to DWARF.  That's a baby step towards
eventually deleting it.

Simon

Re: Default debug format for AVR

[Jeff Law]

On 4/8/2021 8:06 AM, Simon Marchi via Gcc wrote:
> On 2021-04-08 9:11 a.m., David Edelsohn wrote:
>>>> AIX continues to use and support STABS, although it is transitioning
>>>> to DWARF.  If this is intended as a general statement about removal of
>>>> STABS support in GCC,
>>> Yes, it is.
>>>
>>> Richard.
>> Richard,
>>
>> It is inappropriate to unilaterally make this decision without
>> discussion with all affected ports and maintainers, without warning,
>> and without deprecation.  I request that you rescind this decision.
>>
>> It is somewhat ironic to act as a dictator when we are having a
>> discussion about dictatorial behavior in GCC leadership.
> I don't really want to start such a debate about GCC politics.  If stabs
> is not ready to be deleted, that's fine.  But it would be good to go
> through all targets for which it is the default (like avr), and see if
> they are ready to be switched to DWARF.  That's a baby step towards
> eventually deleting it.

Agreed.  I'd bet AIX is the outlier here and that most, if not all, 
other ports that may currently be stabs-by-default can switch to 
dwarf-by-default with no significant fallout.  So we fix everything we 
can while we wait for AIX to move forward.


jeff

Re: Default debug format for AVR

[David Edelsohn]

On Thu, Apr 8, 2021 at 10:41 AM Jeff Law <jeffreyalaw@gmail.com> wrote:
>
> On 4/8/2021 8:06 AM, Simon Marchi via Gcc wrote:
> > On 2021-04-08 9:11 a.m., David Edelsohn wrote:
> >>>> AIX continues to use and support STABS, although it is transitioning
> >>>> to DWARF.  If this is intended as a general statement about removal of
> >>>> STABS support in GCC,
> >>> Yes, it is.
> >>>
> >>> Richard.
> >> Richard,
> >>
> >> It is inappropriate to unilaterally make this decision without
> >> discussion with all affected ports and maintainers, without warning,
> >> and without deprecation.  I request that you rescind this decision.
> >>
> >> It is somewhat ironic to act as a dictator when we are having a
> >> discussion about dictatorial behavior in GCC leadership.
> > I don't really want to start such a debate about GCC politics.  If stabs
> > is not ready to be deleted, that's fine.  But it would be good to go
> > through all targets for which it is the default (like avr), and see if
> > they are ready to be switched to DWARF.  That's a baby step towards
> > eventually deleting it.
>
> Agreed.  I'd bet AIX is the outlier here and that most, if not all,
> other ports that may currently be stabs-by-default can switch to
> dwarf-by-default with no significant fallout.  So we fix everything we
> can while we wait for AIX to move forward.

I am not requesting a continuation of support for STABS to be
obstinate.  AIX has some support for DWARF, but STABS continues to be
the primary debug format on AIX.  Binutils does not fully function on
AIX and the AIX native tools support for DWARF is incomplete.  Also,
AIX uses XCOFF file format, not ELF, so DWARF syntax needs to be
adapted and all of the tools need to agree on the way that AIX symbols
are represented in DWARF.

IBM is adding support for AIX to LLVM and LLVM does not support STABS
debugging, which has both exposed problems and is motivating work to
resolve the gaps, but the additional features and fixes require time
to implement and deploy.

I am eager to transition to DWARF on AIX, but I continue to ask that
the support not be removed until DWARF can be used as a complete
substitute on AIX.  I hope that full support for DWARF in AIX will be
completed in 2022 and removal of GCC support for STABS can be targeted
for GCC 13, not GCC 12.

Thanks, David

Re: Default debug format for AVR

[David Edelsohn]

On Thu, Apr 8, 2021 at 12:09 PM David Edelsohn <dje.gcc@gmail.com> wrote:
>
> On Thu, Apr 8, 2021 at 10:41 AM Jeff Law <jeffreyalaw@gmail.com> wrote:
> >
> > On 4/8/2021 8:06 AM, Simon Marchi via Gcc wrote:
> > > On 2021-04-08 9:11 a.m., David Edelsohn wrote:
> > >>>> AIX continues to use and support STABS, although it is transitioning
> > >>>> to DWARF.  If this is intended as a general statement about removal of
> > >>>> STABS support in GCC,
> > >>> Yes, it is.
> > >>>
> > >>> Richard.
> > >> Richard,
> > >>
> > >> It is inappropriate to unilaterally make this decision without
> > >> discussion with all affected ports and maintainers, without warning,
> > >> and without deprecation.  I request that you rescind this decision.
> > >>
> > >> It is somewhat ironic to act as a dictator when we are having a
> > >> discussion about dictatorial behavior in GCC leadership.
> > > I don't really want to start such a debate about GCC politics.  If stabs
> > > is not ready to be deleted, that's fine.  But it would be good to go
> > > through all targets for which it is the default (like avr), and see if
> > > they are ready to be switched to DWARF.  That's a baby step towards
> > > eventually deleting it.
> >
> > Agreed.  I'd bet AIX is the outlier here and that most, if not all,
> > other ports that may currently be stabs-by-default can switch to
> > dwarf-by-default with no significant fallout.  So we fix everything we
> > can while we wait for AIX to move forward.
>
> I am not requesting a continuation of support for STABS to be
> obstinate.  AIX has some support for DWARF, but STABS continues to be
> the primary debug format on AIX.  Binutils does not fully function on
> AIX and the AIX native tools support for DWARF is incomplete.  Also,
> AIX uses XCOFF file format, not ELF, so DWARF syntax needs to be
> adapted and all of the tools need to agree on the way that AIX symbols
> are represented in DWARF.
>
> IBM is adding support for AIX to LLVM and LLVM does not support STABS
> debugging, which has both exposed problems and is motivating work to
> resolve the gaps, but the additional features and fixes require time
> to implement and deploy.
>
> I am eager to transition to DWARF on AIX, but I continue to ask that
> the support not be removed until DWARF can be used as a complete
> substitute on AIX.  I hope that full support for DWARF in AIX will be
> completed in 2022 and removal of GCC support for STABS can be targeted
> for GCC 13, not GCC 12.
>

I have discussed the STABS debugging situation internally and the AIX
team has accepted that STABS support will be removed in GCC 12.  This
also will mean that I will remove the AIX 6.1 and AIX 7.1
configurations for GCC 12.

If you want to delete all STABS debugging support in Stage 1, go ahead.

Thanks, David

Re: Default debug format for AVR

[Jeff Law]

>> Agreed.  I'd bet AIX is the outlier here and that most, if not all,
>> other ports that may currently be stabs-by-default can switch to
>> dwarf-by-default with no significant fallout.  So we fix everything we
>> can while we wait for AIX to move forward.
> I am not requesting a continuation of support for STABS to be
> obstinate.  AIX has some support for DWARF, but STABS continues to be
> the primary debug format on AIX.  Binutils does not fully function on
> AIX and the AIX native tools support for DWARF is incomplete.  Also,
> AIX uses XCOFF file format, not ELF, so DWARF syntax needs to be
> adapted and all of the tools need to agree on the way that AIX symbols
> are represented in DWARF.

Just to be clear, I didn't think you were being obstinate at all.  I was 
just pointing out that I think the other ports can and probably should 
change now (well, start of gcc-12 cycle), but that AIX can't yet.

Jeff