[PATCH] Fix assertion for unwind-dw2-fde.c btree changes

[Richard Biener]

On Sun, May 14, 2023 at 9:00 PM Thomas Neumann via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> Dear Sören,
>
> > we ran into a regression introduced by these changes. The regression
> > manifests itself in a failing assertion in __deregister_frame_info_bases.
> > The assertion failure was observed while using Chromium's `flatc` build
> > system tool. The failing assertion is:
> >
> >       unwind-dw2-fde.c:281    gcc_assert (in_shutdown || ob);
> > [snip]
> > However, I believe there is one more edge case that isn't being account
> > for presently: If the inserted entry has a size of 0 (i.e. if range[1] -
> > range[0] == 0) then the btree_insert call in __register_frame_info_bases
> > will not insert anything. This is not accounted for in
>  > [snip]
> >
> > Would be cool if this could be fixed on the GCC trunk.
>
> thanks for the details analysis and the patch, it looks obviously
> correct for me. I can apply it to trunk, but we need approval from a gcc
> maintainer first.

The patch is OK for trunk and affected branches.

Thanks,
Richard.

> But independent of your patch, do you have the test case available in
> some easily accessible form, for example a docker image or an automated
> build script? I ask because something odd is happening here, somebody
> registered a non-empty EH that does not contain a single unwind range. I
> am puzzled why anybody would do that, I would like to double check that
> this is indeed the intended behavior and not a bug somewhere else. Or if
> you have the test case at hand, it would be great if you could do a
> quick step through get_pc_range for the affected frame to double-check
> that the table is indeed empty and we don't miss an entry for some
> strange reason.
>
> Best
>
> Thomas
>
>
>