[RFC PATCH 6/9] btf_encoder: collect elf_functions in btf_encoder__pre_load_module

[Ihor Solodrai <ihor.solodrai@xxxxx>]

Introduce a global elf_functions_list variable in btf_encoder.c that
contains an elf_functions per ELF.

An elf_functions structure is allocated and filled out by
btf_encoder__pre_load_module() hook, and the list is cleared after
btf_encoder__encode() is done.

At this point btf_encoders don't use shared elf_functions yet (each
maintains their own copy as before), but it is built before encoders
are initialized.

Signed-off-by: Ihor Solodrai <ihor.solodrai@xxxxx>
---
 btf_encoder.c | 66 +++++++++++++++++++++++++++++++++++++++++++++++++++
 btf_encoder.h |  2 ++
 pahole.c      |  3 +++
 3 files changed, 71 insertions(+)

diff --git a/btf_encoder.c b/btf_encoder.c
index 8331efe..8b1db5b 100644
--- a/btf_encoder.c
+++ b/btf_encoder.c
@@ -103,6 +103,8 @@ struct elf_secinfo {
 };
 
 struct elf_functions {
+	struct list_head node; /* for elf_functions_list */
+	Elf *elf; /* source ELF */
 	struct elf_symtab *symtab;
 	struct elf_function *entries;
 	int cnt;
@@ -149,6 +151,67 @@ struct btf_kfunc_set_range {
 	uint64_t end;
 };
 
+
+/* In principle, multiple ELFs can be processed in one pahole run,
+ * so we have to store elf_functions table per ELF.
+ * An element is added to the list on btf_encoder__pre_load_module,
+ * and removed after btf_encoder__encode is done.
+ */
+static LIST_HEAD(elf_functions_list);
+
+static inline void elf_functions__delete(struct elf_functions *funcs)
+{
+	free(funcs->entries);
+	elf_symtab__delete(funcs->symtab);
+	list_del(&funcs->node);
+	free(funcs);
+}
+
+static inline void elf_functions__delete_all(void)
+{
+	struct list_head *pos, *tmp;
+
+	list_for_each_safe(pos, tmp, &elf_functions_list) {
+		struct elf_functions *funcs = list_entry(pos, struct elf_functions, node);
+
+		elf_functions__delete(funcs);
+	}
+}
+
+static int elf_functions__collect(struct elf_functions *functions);
+
+int btf_encoder__pre_load_module(Dwfl_Module *mod, Elf *elf)
+{
+	struct elf_functions *funcs;
+	int err;
+
+	funcs = calloc(1, sizeof(*funcs));
+	if (!funcs) {
+		err = -ENOMEM;
+		goto out_delete;
+	}
+
+	funcs->symtab = elf_symtab__new(NULL, elf);
+	if (!funcs->symtab) {
+		err = -1;
+		goto out_delete;
+	}
+
+	funcs->elf = elf;
+	err = elf_functions__collect(funcs);
+	if (err)
+		goto out_delete;
+
+	list_add_tail(&funcs->node, &elf_functions_list);
+
+	return 0;
+
+out_delete:
+	elf_functions__delete(funcs);
+	return err;
+}
+
+
 static LIST_HEAD(encoders);
 static pthread_mutex_t encoders__lock = PTHREAD_MUTEX_INITIALIZER;
 
@@ -2107,6 +2170,8 @@ int btf_encoder__encode(struct btf_encoder *encoder)
 #endif
 		err = btf_encoder__write_elf(encoder, encoder->btf, BTF_ELF_SEC);
 	}
+
+	elf_functions__delete_all();
 	return err;
 }
 
@@ -2424,6 +2489,7 @@ struct btf_encoder *btf_encoder__new(struct cu *cu, const char *detached_filenam
 			goto out;
 		}
 		encoder->functions.symtab = encoder->symtab;
+		encoder->functions.elf = cu->elf;
 
 		/* index the ELF sections for later lookup */
 
diff --git a/btf_encoder.h b/btf_encoder.h
index 824963b..7debd67 100644
--- a/btf_encoder.h
+++ b/btf_encoder.h
@@ -34,4 +34,6 @@ 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__pre_load_module(Dwfl_Module *mod, Elf *elf);
+
 #endif /* _BTF_ENCODER_H_ */
diff --git a/pahole.c b/pahole.c
index fa5d8c7..1f8cf4b 100644
--- a/pahole.c
+++ b/pahole.c
@@ -3737,6 +3737,9 @@ int main(int argc, char *argv[])
 		conf_load.threads_collect = pahole_threads_collect;
 	}
 
+	if (btf_encode)
+		conf_load.pre_load_module = btf_encoder__pre_load_module;
+
 	// Make 'pahole --header type < file' a shorter form of 'pahole -C type --count 1 < file'
 	if (conf.header_type && !class_name && prettify_input) {
 		conf.count = 1;
-- 
2.47.0