kernel/trace/trace_btf.c

   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