Re: [PATCH 1/2] btf_encoder: Make encoding vars into BTF optional.

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

Em Fri, Sep 18, 2020 at 01:40:57PM -0700, Hao Luo escreveu:
> Introduce an option --btf_encode_symbols to pahole so that pahole
> will only encode global symbols upon request. On the kernel side,
> we can add a Kconfig to turn on this feature. This would make the
> rollout of pahole v1.18 safe against potential bugs in the feature
> introduced in commit f3d9054ba8ff ("btf_encoder: Teach pahole to
> store percpu variables in vmlinux BTF.").

'encode_symbols' is too generic, please rename it to
encode_global_symbols or something like that.

- Arnaldo
 
> Signed-off-by: Hao Luo <haoluo@google.com>
> ---
>  btf_encoder.c |  5 ++++-
>  btf_encoder.h |  2 +-
>  pahole.c      | 11 ++++++++++-
>  3 files changed, 15 insertions(+), 3 deletions(-)
> 
> diff --git a/btf_encoder.c b/btf_encoder.c
> index 982f59d..54ffdd1 100644
> --- a/btf_encoder.c
> +++ b/btf_encoder.c
> @@ -237,7 +237,7 @@ static struct variable *hashaddr__find_variable(const struct hlist_head hashtabl
>  	return NULL;
>  }
>  
> -int cu__encode_btf(struct cu *cu, int verbose, bool force)
> +int cu__encode_btf(struct cu *cu, int verbose, bool force, bool encode_symbols)
>  {
>  	bool add_index_type = false;
>  	uint32_t type_id_off;
> @@ -314,6 +314,9 @@ int cu__encode_btf(struct cu *cu, int verbose, bool force)
>  		}
>  	}
>  
> +	/* if there is no request to encode symbols, just finish. */
> +	if (!encode_symbols)
> +		goto out;
>  
>  	if (btfe->percpu_shndx == 0 || !btfe->symtab)
>  		goto out;
> diff --git a/btf_encoder.h b/btf_encoder.h
> index bca2348..f2e95fe 100644
> --- a/btf_encoder.h
> +++ b/btf_encoder.h
> @@ -13,6 +13,6 @@ struct cu;
>  
>  int btf_encoder__encode();
>  
> -int cu__encode_btf(struct cu *cu, int verbose, bool force);
> +int cu__encode_btf(struct cu *cu, int verbose, bool force, bool encode_symbols);
>  
>  #endif /* _BTF_ENCODER_H_ */
> diff --git a/pahole.c b/pahole.c
> index e1cde61..079d951 100644
> --- a/pahole.c
> +++ b/pahole.c
> @@ -26,6 +26,7 @@
>  static bool btf_encode;
>  static bool ctf_encode;
>  static bool first_obj_only;
> +static bool btf_encode_symbols;
>  
>  static uint8_t class__include_anonymous;
>  static uint8_t class__include_nested_anonymous;
> @@ -809,6 +810,7 @@ ARGP_PROGRAM_VERSION_HOOK_DEF = dwarves_print_version;
>  #define ARGP_header_type	   314
>  #define ARGP_size_bytes		   315
>  #define ARGP_range		   316
> +#define ARGP_btf_encode_symbols	   317
>  
>  static const struct argp_option pahole__options[] = {
>  	{
> @@ -1087,6 +1089,11 @@ static const struct argp_option pahole__options[] = {
>  		.key  = 'J',
>  		.doc  = "Encode as BTF",
>  	},
> +	{
> +		.name = "btf_encode_symbols",
> +		.key  = ARGP_btf_encode_symbols,
> +		.doc  = "Encode global symbols in BTF. Off by default."
> +	},
>  	{
>  		.name = "force",
>  		.key  = 'j',
> @@ -1207,6 +1214,8 @@ static error_t pahole__options_parser(int key, char *arg,
>  		conf.range = arg;			break;
>  	case ARGP_header_type:
>  		conf.header_type = arg;			break;
> +	case ARGP_btf_encode_symbols:
> +		btf_encode_symbols = true;		break;
>  	default:
>  		return ARGP_ERR_UNKNOWN;
>  	}
> @@ -2352,7 +2361,7 @@ static enum load_steal_kind pahole_stealer(struct cu *cu,
>  		goto filter_it;
>  
>  	if (btf_encode) {
> -		cu__encode_btf(cu, global_verbose, force);
> +		cu__encode_btf(cu, global_verbose, force, btf_encode_symbols);
>  		return LSK__KEEPIT;
>  	}
>  
> -- 
> 2.28.0.681.g6f77f65b4e-goog
> 

-- 

- Arnaldo