[RFC dwarves 4/6] btf_encoder: add "addr=0x<addr>" function declaration tag if --btf_gen_func_addr specified

[Alan Maguire <alan.maguire@oracle.com>]

Now that we have address information, use BTF declaration tag
of form

[105031] DECL_TAG 'address=0xffffffff81777410' type_id=105030 component_idx=-1

...which points at the function in question.

Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
---
 btf_encoder.c | 34 +++++++++++++++++++++++++---------
 btf_encoder.h |  4 ++--
 dwarves.h     |  1 +
 pahole.c      | 12 ++++++++++--
 4 files changed, 38 insertions(+), 13 deletions(-)

diff --git a/btf_encoder.c b/btf_encoder.c
index edf72e6..3bd0fe0 100644
--- a/btf_encoder.c
+++ b/btf_encoder.c
@@ -99,7 +99,7 @@ struct btf_encoder {
 static LIST_HEAD(encoders);
 static pthread_mutex_t encoders__lock = PTHREAD_MUTEX_INITIALIZER;
 
-static void btf_encoder__add_saved_funcs(struct btf_encoder *encoder);
+static void btf_encoder__add_saved_funcs(struct btf_encoder *encoder, struct conf_load *conf_load);
 
 /* mutex only needed for add/delete, as this can happen in multiple encoding
  * threads.  Traversal of the list is currently confined to thread collection.
@@ -710,7 +710,7 @@ static int32_t btf_encoder__add_var_secinfo(struct btf_encoder *encoder, uint32_
 	return gobuffer__add(&encoder->percpu_secinfo, &si, sizeof(si));
 }
 
-int32_t btf_encoder__add_encoder(struct btf_encoder *encoder, struct btf_encoder *other)
+int32_t btf_encoder__add_encoder(struct btf_encoder *encoder, struct btf_encoder *other, struct conf_load *conf_load)
 {
 	struct gobuffer *var_secinfo_buf = &other->percpu_secinfo;
 	size_t sz = gobuffer__size(var_secinfo_buf);
@@ -723,7 +723,7 @@ int32_t btf_encoder__add_encoder(struct btf_encoder *encoder, struct btf_encoder
 	if (encoder == other)
 		return 0;
 
-	btf_encoder__add_saved_funcs(other);
+	btf_encoder__add_saved_funcs(other, conf_load);
 
 	for (i = 0; i < nr_var_secinfo; i++) {
 		vsi = (struct btf_var_secinfo *)var_secinfo_buf->entries + i;
@@ -881,7 +881,7 @@ static int32_t btf_encoder__save_func(struct btf_encoder *encoder, struct functi
 	return 0;
 }
 
-static int32_t btf_encoder__add_func(struct btf_encoder *encoder, struct function *fn)
+static int32_t btf_encoder__add_func(struct btf_encoder *encoder, struct function *fn, struct conf_load *conf_load)
 {
 	int btf_fnproto_id, btf_fn_id, tag_type_id;
 	struct llvm_annotation *annot;
@@ -903,10 +903,26 @@ static int32_t btf_encoder__add_func(struct btf_encoder *encoder, struct functio
 			return -1;
 		}
 	}
+	if (conf_load->btf_gen_func_addr) {
+		if (fn->low_pc) {
+			char addr_tag[64];
+
+			snprintf(addr_tag, sizeof(addr_tag), "address=0x%lx", fn->low_pc);
+			tag_type_id = btf_encoder__add_decl_tag(encoder, addr_tag, btf_fn_id, -1);
+			if (tag_type_id < 0) {
+				fprintf(stderr, "error: failed to encode tag '%s' to func %s\n",
+					addr_tag, name);
+				return -1;
+			}
+		} else {
+			if (encoder->verbose)
+				printf("no addr info for func '%s'\n", name);
+		}
+	}
 	return 0;
 }
 
-static void btf_encoder__add_saved_funcs(struct btf_encoder *encoder)
+static void btf_encoder__add_saved_funcs(struct btf_encoder *encoder, struct conf_load *conf_load)
 {
 	int i;
 
@@ -956,7 +972,7 @@ static void btf_encoder__add_saved_funcs(struct btf_encoder *encoder)
 			}
 		} else {
 			encoder->type_id_off = func->state.type_id_off;
-			btf_encoder__add_func(encoder, fn);
+			btf_encoder__add_func(encoder, fn, conf_load);
 		}
 		fn->proto.processed = 1;
 	}
@@ -1356,12 +1372,12 @@ out:
 	return err;
 }
 
-int btf_encoder__encode(struct btf_encoder *encoder)
+int btf_encoder__encode(struct btf_encoder *encoder, struct conf_load *conf_load)
 {
 	int err;
 
 	/* for single-threaded case, saved funcs are added here */
-	btf_encoder__add_saved_funcs(encoder);
+	btf_encoder__add_saved_funcs(encoder, conf_load);
 
 	if (gobuffer__size(&encoder->percpu_secinfo) != 0)
 		btf_encoder__add_datasec(encoder, PERCPU_SECTION);
@@ -1871,7 +1887,7 @@ int btf_encoder__encode_cu(struct btf_encoder *encoder, struct cu *cu, struct co
 		if (save)
 			err = btf_encoder__save_func(encoder, fn, func);
 		else
-			err = btf_encoder__add_func(encoder, fn);
+			err = btf_encoder__add_func(encoder, fn, conf_load);
 		if (err)
 			goto out;
 	}
diff --git a/btf_encoder.h b/btf_encoder.h
index 34516bb..b5440cd 100644
--- a/btf_encoder.h
+++ b/btf_encoder.h
@@ -19,12 +19,12 @@ struct list_head;
 struct btf_encoder *btf_encoder__new(struct cu *cu, const char *detached_filename, struct btf *base_btf, bool skip_encoding_vars, bool force, bool gen_floats, bool verbose);
 void btf_encoder__delete(struct btf_encoder *encoder);
 
-int btf_encoder__encode(struct btf_encoder *encoder);
+int btf_encoder__encode(struct btf_encoder *encoder, struct conf_load *conf_load);
 
 int btf_encoder__encode_cu(struct btf_encoder *encoder, struct cu *cu, struct conf_load *conf_load);
 
 struct btf *btf_encoder__btf(struct btf_encoder *encoder);
 
-int btf_encoder__add_encoder(struct btf_encoder *encoder, struct btf_encoder *other);
+int btf_encoder__add_encoder(struct btf_encoder *encoder, struct btf_encoder *other, struct conf_load *conf_load);
 
 #endif /* _BTF_ENCODER_H_ */
diff --git a/dwarves.h b/dwarves.h
index 9cf13dd..8486cfc 100644
--- a/dwarves.h
+++ b/dwarves.h
@@ -68,6 +68,7 @@ struct conf_load {
 	bool			skip_encoding_btf_enum64;
 	bool			btf_gen_optimized;
 	bool			skip_encoding_btf_inconsistent_proto;
+	bool			btf_gen_func_addr;
 	uint8_t			hashtable_bits;
 	uint8_t			max_hashtable_bits;
 	uint16_t		kabi_prefix_len;
diff --git a/pahole.c b/pahole.c
index 6fc4ed6..b799ea6 100644
--- a/pahole.c
+++ b/pahole.c
@@ -1232,6 +1232,7 @@ 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_gen_func_addr 341
 
 static const struct argp_option pahole__options[] = {
 	{
@@ -1654,6 +1655,11 @@ 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_gen_func_addr",
+		.key = ARGP_btf_gen_func_addr,
+		.doc = "Encode function addresses as a BTF declaration tag pointing at the function; this allows easier matching of BTF function descriptions to kernel function addresses."
+	},
 	{
 		.name = NULL,
 	}
@@ -1829,6 +1835,8 @@ 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_gen_func_addr:
+		conf_load.btf_gen_func_addr = true;		break;
 	default:
 		return ARGP_ERR_UNKNOWN;
 	}
@@ -3009,7 +3017,7 @@ static int pahole_threads_collect(struct conf_load *conf, int nr_threads, void *
                 */
 		if (!threads[i]->btf)
 			continue;
-		err = btf_encoder__add_encoder(btf_encoder, threads[i]->encoder);
+		err = btf_encoder__add_encoder(btf_encoder, threads[i]->encoder, conf);
 		if (err < 0)
 			goto out;
 	}
@@ -3567,7 +3575,7 @@ try_sole_arg_as_class_names:
 	header = NULL;
 
 	if (btf_encode && btf_encoder) { // maybe all CUs were filtered out and thus we don't have an encoder?
-		err = btf_encoder__encode(btf_encoder);
+		err = btf_encoder__encode(btf_encoder, &conf_load);
 		if (err) {
 			fputs("Failed to encode BTF\n", stderr);
 			goto out_cus_delete;
-- 
2.31.1