Re: [PATCH v2] pahole: Apply CU-level filters early in loading

Alan Maguire
2024-08-06T12:10:21Z

On 01/08/2024 19:50, 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.
>
> Signed-off-by: Matthew Maurer <mmaurer@google.com>

LGTM, thanks!

Reviewed-by: Alan Maguire <alan.maguire@oracle.com>
Tested-by: Alan Maguire <alan.maguire@oracle.com>

> ---
> dwarf_loader.c | 10 ++++++++++
> dwarves.h | 1 +
> pahole.c | 4 ++++
> 3 files changed, 15 insertions(+)
>
> diff --git a/dwarf_loader.c b/dwarf_loader.c
> index b832c93..02a17f4 100644
> --- a/dwarf_loader.c
> +++ b/dwarf_loader.c
> @@ -2854,6 +2854,16 @@ static int die__process(Dwarf_Die *die, struct cu *cu, struct conf_load *conf)
>
> cu->language = attr_numeric(die, DW_AT_language);
>
> + if (conf->early_cu_filter)
> + cu = conf->early_cu_filter(cu);
> +
> + /*
> + * If we filtered this CU out, we still want to keep iterating, but
> + * there's no need to walk the rest of the CU info.
> + */
> + if (cu == NULL)
> + return DWARF_CB_OK;
> +
> if (dwarf_child(die, &child) == 0) {
> int err = die__process_unit(&child, cu, conf);
> if (err)
> diff --git a/dwarves.h b/dwarves.h
> index f5ae79f..92d102b 100644
> --- a/dwarves.h
> +++ b/dwarves.h
> @@ -72,6 +72,7 @@ struct conf_load {
> enum load_steal_kind (*steal)(struct cu *cu,
> struct conf_load *conf,
> void *thr_data);
> + struct cu * (*early_cu_filter)(struct cu *cu);
> int (*thread_exit)(struct conf_load *conf, void *thr_data);
> void *cookie;
> char *format_path;
> diff --git a/pahole.c b/pahole.c
> index 954498d..42a9c16 100644
> --- a/pahole.c
> +++ b/pahole.c
> @@ -3765,6 +3765,10 @@ int main(int argc, char *argv[])
> memset(tab, ' ', sizeof(tab) - 1);
>
> conf_load.steal = pahole_stealer;
> +
> + if (languages.exclude)
> + conf_load.early_cu_filter = cu__filter;
> +
> conf_load.thread_exit = pahole_thread_exit;
>
> if (conf_load.reproducible_build) {