Commit 302db0f5 authored by Masami Hiramatsu (Google)'s avatar Masami Hiramatsu (Google)
Browse files

tracing/probes: Add a function to search a member of a struct/union 

Add btf_find_struct_member() API to search a member of a given data structure
or union from the member's name.

Link: https://lore.kernel.org/all/169272156248.160970.8868479822371129043.stgit@devnote2/



Signed-off-by: default avatarMasami Hiramatsu (Google) <mhiramat@kernel.org>
Reviewed-by: default avatarAlan Maguire <alan.maguire@oracle.com>
Acked-by: default avatarSteven Rostedt (Google) <rostedt@goodmis.org>
parent ebeed8d4

kernel/trace/trace_btf.c

+69 −0
Original line number Diff line number Diff line 
// SPDX-License-Identifier: GPL-2.0

#include <linux/btf.h>

#include <linux/kernel.h>

#include <linux/slab.h>



#include "trace_btf.h"
@@ -51,3 +52,71 @@ const struct btf_param *btf_get_func_param(const struct btf_type *func_proto, s3 
		return NULL;

}



#define BTF_ANON_STACK_MAX	16



struct btf_anon_stack {

	u32 tid;

	u32 offset;

};



/*

 * Find a member of data structure/union by name and return it.

 * Return NULL if not found, or -EINVAL if parameter is invalid.

 * If the member is an member of anonymous union/structure, the offset

 * of that anonymous union/structure is stored into @anon_offset. Caller

 * can calculate the correct offset from the root data structure by

 * adding anon_offset to the member's offset.

 */

const struct btf_member *btf_find_struct_member(struct btf *btf,

						const struct btf_type *type,

						const char *member_name,

						u32 *anon_offset)

{

	struct btf_anon_stack *anon_stack;

	const struct btf_member *member;

	u32 tid, cur_offset = 0;

	const char *name;

	int i, top = 0;



	anon_stack = kcalloc(BTF_ANON_STACK_MAX, sizeof(*anon_stack), GFP_KERNEL);

	if (!anon_stack)

		return ERR_PTR(-ENOMEM);



retry:

	if (!btf_type_is_struct(type)) {

		member = ERR_PTR(-EINVAL);

		goto out;

	}



	for_each_member(i, type, member) {

		if (!member->name_off) {

			/* Anonymous union/struct: push it for later use */

			type = btf_type_skip_modifiers(btf, member->type, &tid);

			if (type && top < BTF_ANON_STACK_MAX) {

				anon_stack[top].tid = tid;

				anon_stack[top++].offset =

					cur_offset + member->offset;

			}

		} else {

			name = btf_name_by_offset(btf, member->name_off);

			if (name && !strcmp(member_name, name)) {

				if (anon_offset)

					*anon_offset = cur_offset;

				goto out;

			}

		}

	}

	if (top > 0) {

		/* Pop from the anonymous stack and retry */

		tid = anon_stack[--top].tid;

		cur_offset = anon_stack[top].offset;

		type = btf_type_by_id(btf, tid);

		goto retry;

	}

	member = NULL;



out:

	kfree(anon_stack);

	return member;

}

kernel/trace/trace_btf.h

+4 −0
Original line number Diff line number Diff line
@@ -5,3 +5,7 @@ const struct btf_type *btf_find_func_proto(const char *func_name, 
					   struct btf **btf_p);

const struct btf_param *btf_get_func_param(const struct btf_type *func_proto,

					   s32 *nr);

const struct btf_member *btf_find_struct_member(struct btf *btf,

						const struct btf_type *type,

						const char *member_name,

						u32 *anon_offset);