Re: [PATCH] Revert "gdb: change blockvector::contains() to handle blockvectors with "holes""

["Jan Vraný" <Jan.Vrany@labware.com>]

On Mon, 2025-12-15 at 07:49 -0700, Tom Tromey wrote:
> > > > > > "Jan" == Jan Vrany <jan.vrany@labware.com> writes:
> 
> Jan> This reverts commit cc1fc6af4150b19f9c4c70d0463ff498703fb637, since it
> Jan> causes a number of regressions that seem not to be easily fixable.
> 
> I hate to revert this since I think it's a better direction for gdb.

Yeah, me too.
> 
> I guess I think the 'lookup' and 'contains' methods should be
> equivalent, and neither should ever return the global or static block --
> only real code blocks.
> 
> Jan> The problem lies in existence of "freestanding" code, a code that is
> Jan> part of a CU but does not have any block associated with it. Consider
> Jan> following program:
> ...
> Jan> When compiled, the foo function has no block of itself:
> 
> FWIW this is what I would expect.  It's just like any other case where a
> function does not have debug info: no debug info mean no block.
> 
> Jan> Thiago suggested to use minsymbols to tell whether or a CU contains
> Jan> given address. I do not think this would work reliably as minsymbols do
> Jan> no know to which CU they belong. In slightly more complicated case of
> Jan> interleaved CUs it does not seem to be possible to tell for sure to which
> Jan> one a given minsymbol belongs.
> 
> The don't know the CU but at you should still be able to set a
> breakpoint on them.
> 
> Anyway, I'd be willing to approve the backout on the basis that it
> causes some regression.  But still I question whether it really makes
> sense, and if it would be better instead to change the test.

We can change tests but I think GDB would still be broken - the problem is that
this change confuses unwinder in a way I do not really understand yet. So it seems to
me that if we keep this, we need "fix" some other part of GDB too. I spent some time
debugging this and tried again yesterday but so far the more I debug the less 
I understand :-(

I do not know what's the policy regarding regressions. If everyone can tolerate 
these regressions for longer, I can try to do some more debugging and see.

Jan

> 
> Tom