This allows consumers to specify an opt-in set of features
they want to use in BTF encoding.
Supported features are a comma-separated combination of
encode_force Ignore invalid symbols when encoding BTF.
var Encode variables using BTF_KIND_VAR in BTF.
float Encode floating-point types in BTF.
decl_tag Encode declaration tags using BTF_KIND_DECL_TAG.
type_tag Encode type tags using BTF_KIND_TYPE_TAG.
enum64 Encode enum64 values with BTF_KIND_ENUM64.
optimized_func Encode representations of optimized functions
with suffixes like ".isra.0" etc
consistent_func Avoid encoding inconsistent static functions.
These occur when a parameter is optimized out
in some CUs and not others, or when the same
function name has inconsistent BTF descriptions
in different CUs.
Specifying "--btf_features=all" is the equivalent to setting
all of the above. If pahole does not know about a feature
specified in --btf_features it silently ignores it.
The --btf_features can either be specified via a single comma-separated
list
--btf_features=enum64,float
...or via multiple --btf_features values
--btf_features=enum64 --btf_features=float
These properties allow us to use the --btf_features option in
the kernel scripts/pahole_flags.sh script to specify the desired
set of BTF features.
If a feature named in --btf_features is not present in the version
of pahole used, BTF encoding will not complain. This is desired
because it means we no longer have to tie new features to a specific
pahole version.
Suggested-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
Signed-off-by: Alan Maguire <alan.maguire@xxxxxxxxxx>
---
man-pages/pahole.1 | 24 ++++++++++
pahole.c | 114 ++++++++++++++++++++++++++++++++++++++++++++-
2 files changed, 137 insertions(+), 1 deletion(-)
diff --git a/man-pages/pahole.1 b/man-pages/pahole.1
index c1b48de..a09885f 100644
--- a/man-pages/pahole.1
+++ b/man-pages/pahole.1
@@ -273,6 +273,30 @@ Generate BTF for functions with optimization-related suffixes (.isra, .constprop
.B \-\-btf_gen_all
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
+
+.nf
+ encode_force Ignore invalid symbols when encoding BTF; for example
+ if a symbol has an invalid name, it will be ignored
+ and BTF encoding will continue.
+ var Encode variables using BTF_KIND_VAR in BTF.
+ float Encode floating-point types in BTF.
+ decl_tag Encode declaration tags using BTF_KIND_DECL_TAG.
+ type_tag Encode type tags using BTF_KIND_TYPE_TAG.
+ enum64 Encode enum64 values with BTF_KIND_ENUM64.
+ optimized_func Encode representations of optimized functions
+ with suffixes like ".isra.0".
+ consistent_func Avoid encoding inconsistent static functions.
+ These occur when a parameter is optimized out
+ in some CUs and not others, or when the same
+ function name has inconsistent BTF descriptions
+ in different CUs.
+.fi
+
+So for example, specifying \-\-btf_encode=var,enum64 will result in a BTF encoding that (as well as encoding basic BTF information) will contain variables and enum64 values.
+
.TP
.B \-l, \-\-show_first_biggest_size_base_type_member
Show first biggest size base_type member.
diff --git a/pahole.c b/pahole.c
index 7a41dc3..0d0f6c6 100644
--- a/pahole.c
+++ b/pahole.c
@@ -1229,6 +1229,110 @@ ARGP_PROGRAM_VERSION_HOOK_DEF = dwarves_print_version;
#define ARGP_skip_emitting_atomic_typedefs 338
#define ARGP_btf_gen_optimized 339
#define ARGP_skip_encoding_btf_inconsistent_proto 340
+#define ARGP_btf_features 341
+
+/* --btf_features=feature1[,feature2,..] allows us to specify
+ * a list of requested BTF features or "all" to enable all features.
+ * These are translated into the appropriate conf_load values via a
+ * struct btf_feature which specifies the associated conf_load
+ * boolean field and whether its default (representing the feature being
+ * off) is false or true.
+ *
+ * btf_features is for opting _into_ features so for a case like
+ * conf_load->btf_gen_floats, the translation is simple; the presence
+ * of the "float" feature in --btf_features sets conf_load->btf_gen_floats
+ * to true.
+ *
+ * The more confusing case is for features that are enabled unless
+ * skipping them is specified; for example
+ * conf_load->skip_encoding_btf_type_tag. By default - to support
+ * the opt-in model of only enabling features the user asks for -
+ * conf_load->skip_encoding_btf_type_tag is set to true (meaning no
+ * type_tags) and it is only set to false if --btf_features contains
+ * the "type_tag" keyword.
+ *
+ * So from the user perspective, all features specified via
+ * --btf_features are enabled, and if a feature is not specified,
+ * it is disabled.
+ *
+ * If --btf_features is not used, the usual pahole defaults for
+ * 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 }
+
+struct btf_feature {
+ const char *name;
+ const char *option_alias;
+ bool *conf_value;
+ bool default_value;
+} 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),
+};
+
+#define BTF_MAX_FEATURES 32
+#define BTF_MAX_FEATURE_STR 1024
+
+bool set_btf_features_defaults;
+
+/* Translate --btf_features=feature1[,feature2] into conf_load values.
+ * Explicitly ignores unrecognized features to allow future specification
+ * of new opt-in features.
+ */
+static void parse_btf_features(const char *features)
+{
+ char *feature_list[BTF_MAX_FEATURES] = {};
+ char f[BTF_MAX_FEATURE_STR];
+ bool encode_all = false;
+ int i, j, n = 0;
+
+ strncpy(f, features, sizeof(f));
+
+ if (strcmp(features, "all") == 0) {
+ encode_all = true;
+ } else {
+ char *saveptr = NULL, *s = f, *t;
+
+ while ((t = strtok_r(s, ",", &saveptr)) != NULL && n < BTF_MAX_FEATURES) {
+ s = NULL;
+ feature_list[n++] = t;
+ }
+ }
+
+ for (i = 0; i < ARRAY_SIZE(btf_features); i++) {
+ bool match = encode_all;
+
+ /* Only set default values once, as multiple --btf_features=
+ * may be specified on command-line, and setting defaults
+ * again could clobber values. The aim is to enable
+ * all features set across all --btf_features options.
+ */
+ if (!set_btf_features_defaults)
+ *(btf_features[i].conf_value) = btf_features[i].default_value;
+ if (!match) {
+ for (j = 0; j < n; j++) {
+ if (strcmp(feature_list[j], btf_features[i].name) == 0) {
+ match = true;
+ break;
+ }
+ }
+ }
+ /* switch "default-off" features on, and "default-on" features
+ * off; i.e. negate the default value.
+ */
+ if (match)
+ *(btf_features[i].conf_value) = !btf_features[i].default_value;
+ }
+ set_btf_features_defaults = true;
+}
static const struct argp_option pahole__options[] = {
{
@@ -1651,6 +1755,12 @@ static const struct argp_option pahole__options[] = {
.key = ARGP_skip_encoding_btf_inconsistent_proto,
.doc = "Skip functions that have multiple inconsistent function prototypes sharing the same name, or that use unexpected registers for parameter values."
},
+ {
+ .name = "btf_features",
+ .key = ARGP_btf_features,
+ .arg = "FEATURE_LIST",
+ .doc = "Specify supported BTF features in FEATURE_LIST or 'all' for all supported features. See the pahole manual page for the list of supported features."
+ },
{
.name = NULL,
}
@@ -1796,7 +1906,7 @@ static error_t pahole__options_parser(int key, char *arg,
case ARGP_btf_gen_floats:
conf_load.btf_gen_floats = true; break;
case ARGP_btf_gen_all:
- conf_load.btf_gen_floats = true; break;
+ parse_btf_features("all"); break;
case ARGP_with_flexible_array:
show_with_flexible_array = true; break;
case ARGP_prettify_input_filename:
@@ -1826,6 +1936,8 @@ static error_t pahole__options_parser(int key, char *arg,
conf_load.btf_gen_optimized = true; break;
case ARGP_skip_encoding_btf_inconsistent_proto:
conf_load.skip_encoding_btf_inconsistent_proto = true; break;
+ case ARGP_btf_features:
+ parse_btf_features(arg); break;
default:
return ARGP_ERR_UNKNOWN;
}
--
2.31.1
