[PATCH 1/5] Don't enable -gvariable-location-views by default for DWARF5.

[Richard Biener]

On Tue, Aug 25, 2020 at 6:05 AM Alexandre Oliva <oliva@adacore.com> wrote:
>
> On Aug 24, 2020, Jakub Jelinek <jakub@redhat.com> wrote:
>
> > On Mon, Aug 24, 2020 at 02:56:54PM +0200, Mark Wielaard wrote:
> >> DWARF5 makes it possible to read loclists tables without consulting
> >> the debuginfo tree by introducing a table header. Adding location views
> >> breaks this (at least for binutils and elfutils). So don't enable
> >> variable-location-views by default if DWARF5 or higher is selected.
>
> > This should be discussed with Alex, CCed.
> > I'd say elfutils/binutils should just show .debug_loclists independent of
> > .debug_info if there are no loc views and use .debug_info otherwise.
>
> I've suggested before that it made sense to me to start emitting
> locviews when there were concrete plans to implement support for them in
> debug info consumers.
>
> Without such plans, it would make more sense to just disable them
> altogether.
>
> Now, if there are any such plans, it is disabling them for the default
> debug format that doesn't make much sense to me; it would seem to make
> more sense to adopt and promote the proposed extension, implemented in
> =incompat5 in GCC, but it would need some implementation work in
> consumers to at least ignore the extension.
>
>
> Red Hat has had me involved in these efforts for over a decade, but I'm
> not aware of its plans any more, and I don't know of anyone else driving
> the implementation of locviews in consumers, so, given the little I
> know, this patch seems like a timid step in a reasonable direction:
> outputting locviews is no use if there are no consumers for it, more so
> when they actively disturb existing standard-compliant consumers.

But then leaving it enabled by default but not with -gdwarf-5 looks odd
and backward to me as well.  If the consensus is there's no use then
please disable them by default everywhere instead.

Richard.

> --
> Alexandre Oliva, happy hacker
> https://FSFLA.org/blogs/lxo/
> Free Software Activist
> GNU Toolchain Engineer