Re: [PATCH] pahole: Apply CU-level filters early in loading

[Arnaldo Carvalho de Melo <acme@kernel.org>]

On Wed, Jul 31, 2024 at 06:43:51PM +0100, Alan Maguire wrote:
> 
> 
> On 31/07/2024 14:26, Arnaldo Carvalho de Melo wrote:
> > On Wed, Jul 31, 2024 at 09:57:25AM +0100, Alan Maguire wrote:
> >> On 30/07/2024 23:43, Matthew Maurer wrote:
> >>> Without this, even with `--lang_exclude=rust` set, running on `vmlinux`
> >>> with `CONFIG_RUST` enabled will lead to errors like:
> >>> die__process_function: tag not supported 0x2f (template_type_parameter)!
> >>> because the filtering doesn't happen until finalization, but unsupported
> >>> tags are reported during loading.
> >>>
> >>> As an added bonus, this should speed up processing of large objects with
> >>> filtered CUs, as their details will no longer be walked.
> >>>
> >>
> >> One question on this; if we are always doing early filtering like this,
> >> should the explicit cu__filter() call be removed from pahole_stealer()?
> > 
> > When I saw the introduction of an extra callback to be used inside the
> > dwarf_loader I thought that it would be used only for this specific
> > language filtering feature, i.e. a defensive approach at implementing
> > this to avoid unintended side effects of doing all filtering at that
> > point, maybe some other feature somehow depends on the cu__filter()
> > being called where it was so far.
> > 
> > But then it is being used for all filtering, so it seems just a way to
> > reduce the patch size...
> > 
> > So I'd keep the cu->early_cu_filter() but would use it only for the
> > language filtering feature, wdyt?
> 
> So if I understand correctly,
> 
> 	if (languages.exclude)
> 		conf_load.early_cu_filter = cu__filter;
> 
> ? Seems reasonable to me. Thanks!

yeah, you got it. So this new early filtering is done for the feature we
have at hand and if other uses of cu__filter() already in place need, we
can transition to this new mechanism that reuses the cu__filter()
function signature/semantics.

- Arnaldo