Re: [RFC PATCH 7/9] btf_encoder: switch to shared elf_functions table

[Eduard Zingerman <eddyz87@gmail.com>]

On Thu, 2024-11-28 at 01:24 +0000, Ihor Solodrai wrote:
> Do not collect functions from ELF for each new btf_encoder, and
> instead set a pointer to a shared elf_functions table, built
> beforehand by btf_encoder__pre_cus__load_module().
> 
> Do not call btf_encoder__add_saved_funcs() on every
> btf_encoder__add_encoder(). Instead, for non-reproducible
> multi-threaded case do that in pahole_threads_collect(), and for
> single-threaded or reproducible_build do that right before
> btf_encoder__encode().
> 
> Signed-off-by: Ihor Solodrai <ihor.solodrai@pm.me>
> ---

Acked-by: Eduard Zingerman <eddyz87@gmail.com>

[...]

> diff --git a/pahole.c b/pahole.c
> index 1f8cf4b..b5aea56 100644
> --- a/pahole.c
> +++ b/pahole.c
> @@ -3185,12 +3185,16 @@ static int pahole_threads_collect(struct conf_load *conf, int nr_threads, void *
>  	if (error)
>  		goto out;
>  
> +	err = btf_encoder__add_saved_funcs(btf_encoder);
> +	if (err < 0)
> +		goto out;
> +
>  	for (i = 0; i < nr_threads; i++) {
>  		/*
>  		 * Merge content of the btf instances of worker threads to the btf
>  		 * instance of the primary btf_encoder.
>                  */
> -		if (!threads[i]->btf)
> +		if (!threads[i]->encoder || !threads[i]->btf)
>  			continue;

When can 'threads[i]->encoder' be NULL? In case if worker thread exits with error?

>  		err = btf_encoder__add_encoder(btf_encoder, threads[i]->encoder);
>  		if (err < 0)

[...]