Re: [PATCH 1/2] [gdb/symtab] Add name_of_main and language_of_main to the DWARF index

[Aaron Merey <amerey@redhat.com>]

Hi Tom,

On Tue, Oct 24, 2023 at 3:43 AM Tom de Vries <tdevries@suse.de> wrote:
>
> There are two paths to writing a .gdb_index:
> - the save gdb-index command
> - the index-cache.
>
> In the former case, it's probably fairly easy to infer the main name and
> language from the current progspace, as you suggest, since
> set_initial_language has been executed already.
>
> In the latter case, writing the index-cache is executed asap in the
> background, and it only waits for the cooked-index to become available.
> So it would have to wait for the result of set_initial_language as well.

Given the possible speed up from having main info in the index,
maybe we are better off waiting for set_initial_language.  If we
are still worried about this delay, we could introduce a gdb command
to control this setting and note somewhere that if disabled the index
may lack main name and language info.

Another approach could be for gcc to emit DW_AT_main_subprogram
for C/C++. I'm not too familiar with that gcc code so I'm not sure how
feasible this is.

> Also (for both cases) some thought will have to go into how to handle
> the case that the initial language is set by the user.  Is that the
> language we want to write into the .gdb_index?  Or do we skip writing it
> in that case?  Or do we try to get the auto-detected initial language by
> running set_initial_language on the main thread at the point that we
> need it?  Or do we try to get the auto-detected initial language in the
> background on a worker thread?

Hmm I'm not sure here. I think we'd be justified in insisting that index
contents should be determined only by the contents of the relevant
binaries.

Aaron