xref: /openbmc/linux/kernel/trace/trace_btf.c (revision 19758688)
1 // SPDX-License-Identifier: GPL-2.0
2 #include <linux/btf.h>
3 #include <linux/kernel.h>
4 #include <linux/slab.h>
5 
6 #include "trace_btf.h"
7 
8 /*
9  * Find a function proto type by name, and return the btf_type with its btf
10  * in *@btf_p. Return NULL if not found.
11  * Note that caller has to call btf_put(*@btf_p) after using the btf_type.
12  */
13 const struct btf_type *btf_find_func_proto(const char *func_name, struct btf **btf_p)
14 {
15 	const struct btf_type *t;
16 	s32 id;
17 
18 	id = bpf_find_btf_id(func_name, BTF_KIND_FUNC, btf_p);
19 	if (id < 0)
20 		return NULL;
21 
22 	/* Get BTF_KIND_FUNC type */
23 	t = btf_type_by_id(*btf_p, id);
24 	if (!t || !btf_type_is_func(t))
25 		goto err;
26 
27 	/* The type of BTF_KIND_FUNC is BTF_KIND_FUNC_PROTO */
28 	t = btf_type_by_id(*btf_p, t->type);
29 	if (!t || !btf_type_is_func_proto(t))
30 		goto err;
31 
32 	return t;
33 err:
34 	btf_put(*btf_p);
35 	return NULL;
36 }
37 
38 /*
39  * Get function parameter with the number of parameters.
40  * This can return NULL if the function has no parameters.
41  * It can return -EINVAL if the @func_proto is not a function proto type.
42  */
43 const struct btf_param *btf_get_func_param(const struct btf_type *func_proto, s32 *nr)
44 {
45 	if (!btf_type_is_func_proto(func_proto))
46 		return ERR_PTR(-EINVAL);
47 
48 	*nr = btf_type_vlen(func_proto);
49 	if (*nr > 0)
50 		return (const struct btf_param *)(func_proto + 1);
51 	else
52 		return NULL;
53 }
54 
55 #define BTF_ANON_STACK_MAX	16
56 
57 struct btf_anon_stack {
58 	u32 tid;
59 	u32 offset;
60 };
61 
62 /*
63  * Find a member of data structure/union by name and return it.
64  * Return NULL if not found, or -EINVAL if parameter is invalid.
65  * If the member is an member of anonymous union/structure, the offset
66  * of that anonymous union/structure is stored into @anon_offset. Caller
67  * can calculate the correct offset from the root data structure by
68  * adding anon_offset to the member's offset.
69  */
70 const struct btf_member *btf_find_struct_member(struct btf *btf,
71 						const struct btf_type *type,
72 						const char *member_name,
73 						u32 *anon_offset)
74 {
75 	struct btf_anon_stack *anon_stack;
76 	const struct btf_member *member;
77 	u32 tid, cur_offset = 0;
78 	const char *name;
79 	int i, top = 0;
80 
81 	anon_stack = kcalloc(BTF_ANON_STACK_MAX, sizeof(*anon_stack), GFP_KERNEL);
82 	if (!anon_stack)
83 		return ERR_PTR(-ENOMEM);
84 
85 retry:
86 	if (!btf_type_is_struct(type)) {
87 		member = ERR_PTR(-EINVAL);
88 		goto out;
89 	}
90 
91 	for_each_member(i, type, member) {
92 		if (!member->name_off) {
93 			/* Anonymous union/struct: push it for later use */
94 			if (btf_type_skip_modifiers(btf, member->type, &tid) &&
95 			    top < BTF_ANON_STACK_MAX) {
96 				anon_stack[top].tid = tid;
97 				anon_stack[top++].offset =
98 					cur_offset + member->offset;
99 			}
100 		} else {
101 			name = btf_name_by_offset(btf, member->name_off);
102 			if (name && !strcmp(member_name, name)) {
103 				if (anon_offset)
104 					*anon_offset = cur_offset;
105 				goto out;
106 			}
107 		}
108 	}
109 	if (top > 0) {
110 		/* Pop from the anonymous stack and retry */
111 		tid = anon_stack[--top].tid;
112 		cur_offset = anon_stack[top].offset;
113 		type = btf_type_by_id(btf, tid);
114 		goto retry;
115 	}
116 	member = NULL;
117 
118 out:
119 	kfree(anon_stack);
120 	return member;
121 }
122 
123