Re: [PATCH dwarves 1/3] pahole: allow --btf_features to not participate in "all"

[Andrii Nakryiko <andrii.nakryiko@gmail.com>]

On Tue, Apr 16, 2024 at 7:38 AM Alan Maguire <alan.maguire@oracle.com> wrote:
>
> Specifying --btf_features=all enables all supported BTF features.
> However there are some features that are non-standard, so we should
> support a way to use them in --btf_features but not participate in
> the set of features enabled by "--btf_features=all".  As part of this,
> also support all used in a list of --btf_features, i.e.
>
> --btf_features=all,nonstandard_feature
>
> Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
> ---
>  man-pages/pahole.1 |  2 +-
>  pahole.c           | 36 +++++++++++++++++++++++-------------
>  2 files changed, 24 insertions(+), 14 deletions(-)
>
> diff --git a/man-pages/pahole.1 b/man-pages/pahole.1
> index 2be165d..2c08e97 100644
> --- a/man-pages/pahole.1
> +++ b/man-pages/pahole.1
> @@ -290,7 +290,7 @@ Allow using all the BTF features supported by pahole.
>
>  .TP
>  .B \-\-btf_features=FEATURE_LIST
> -Encode BTF using the specified feature list, or specify 'all' for all features supported.  This option can be used as an alternative to unsing multiple BTF-related options. Supported features are
> +Encode BTF using the specified feature list, or specify 'all' for all standard features supported.  This option can be used as an alternative to unsing multiple BTF-related options. Supported standard features are
>
>  .nf
>         encode_force       Ignore invalid symbols when encoding BTF; for example
> diff --git a/pahole.c b/pahole.c
> index 77772bb..890ef81 100644
> --- a/pahole.c
> +++ b/pahole.c
> @@ -1266,23 +1266,26 @@ ARGP_PROGRAM_VERSION_HOOK_DEF = dwarves_print_version;
>   * BTF encoding apply; we encode type/decl tags, do not encode
>   * floats, etc.  This ensures backwards compatibility.
>   */
> -#define BTF_FEATURE(name, alias, default_value)                        \
> -       { #name, #alias, &conf_load.alias, default_value }
> +#define BTF_FEATURE(name, alias, default_value, enable_for_all)                \
> +       { #name, #alias, &conf_load.alias, default_value, enable_for_all }
>
>  struct btf_feature {
>         const char      *name;
>         const char      *option_alias;
>         bool            *conf_value;
>         bool            default_value;
> +       bool            enable_for_all; /* some nonstandard features may not
> +                                        * be enabled for --btf_features=all
> +                                        */
>  } btf_features[] = {
> -       BTF_FEATURE(encode_force, btf_encode_force, false),
> -       BTF_FEATURE(var, skip_encoding_btf_vars, true),
> -       BTF_FEATURE(float, btf_gen_floats, false),
> -       BTF_FEATURE(decl_tag, skip_encoding_btf_decl_tag, true),
> -       BTF_FEATURE(type_tag, skip_encoding_btf_type_tag, true),
> -       BTF_FEATURE(enum64, skip_encoding_btf_enum64, true),
> -       BTF_FEATURE(optimized_func, btf_gen_optimized, false),
> -       BTF_FEATURE(consistent_func, skip_encoding_btf_inconsistent_proto, false),
> +       BTF_FEATURE(encode_force, btf_encode_force, false, true),
> +       BTF_FEATURE(var, skip_encoding_btf_vars, true, true),
> +       BTF_FEATURE(float, btf_gen_floats, false, true),
> +       BTF_FEATURE(decl_tag, skip_encoding_btf_decl_tag, true, true),
> +       BTF_FEATURE(type_tag, skip_encoding_btf_type_tag, true, true),
> +       BTF_FEATURE(enum64, skip_encoding_btf_enum64, true, true),
> +       BTF_FEATURE(optimized_func, btf_gen_optimized, false, true),
> +       BTF_FEATURE(consistent_func, skip_encoding_btf_inconsistent_proto, false, true),
>  };

maybe keep those special features in a separate array instead?

it is kind of weird to see --btf_features=all,and_then_some, maybe it
makes sense to have --btf_extras or something for those?

>
>  #define BTF_MAX_FEATURE_STR    1024
> @@ -1350,8 +1353,10 @@ static void parse_btf_features(const char *features, bool strict)
>         if (strcmp(features, "all") == 0) {
>                 int i;
>
> -               for (i = 0; i < ARRAY_SIZE(btf_features); i++)
> -                       enable_btf_feature(&btf_features[i]);
> +               for (i = 0; i < ARRAY_SIZE(btf_features); i++) {
> +                       if (btf_features[i].enable_for_all)
> +                               enable_btf_feature(&btf_features[i]);
> +               }
>                 return;
>         }
>
> @@ -1361,7 +1366,12 @@ static void parse_btf_features(const char *features, bool strict)
>                 struct btf_feature *feature = find_btf_feature(feature_name);
>
>                 if (!feature) {
> -                       if (strict) {
> +                       /* --btf_features=all,nonstandard_feature should be
> +                        * allowed.
> +                        */
> +                       if (strcmp(feature_name, "all") == 0) {
> +                               parse_btf_features(feature_name, strict);
> +                       } else if (strict) {
>                                 fprintf(stderr, "Feature '%s' in '%s' is not supported.  Supported BTF features are:\n",
>                                         feature_name, features);
>                                 show_supported_btf_features(stderr);
> --
> 2.39.3
>
>