include/btf.h

   1 /* Declarations and definitions relating to the BPF Type Format (BTF).
   2    Copyright (C) 2021 Free Software Foundation, Inc.
   3
   4    This file is part of GCC.
   5
   6    GCC is free software; you can redistribute it and/or modify it
   7    under the terms of the GNU General Public License as published by
   8    the Free Software Foundation; either version 3, or (at your option)
   9    any later version.
  10
  11    GCC is distributed in the hope that it will be useful, but WITHOUT
  12    ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
  13    or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public
  14    License for more details.
  15
  16    You should have received a copy of the GNU General Public License
  17    along with GCC; see the file COPYING3.  If not see
  18    <http://www.gnu.org/licenses/>.  */
  19
  20 /* This file is derived from the BTF specification described in the
  21    Linux kernel source tree (linux/Documentation/bpf/btf.rst).  */
  22
  23 #ifndef _BTF_H_
  24 #define _BTF_H_
  25
  26 #include <stdint.h>
  27
  28 #ifdef  __cplusplus
  29 extern "C"
  30 {
  31 #endif
  32
  33 /* BTF magic number to identify header, endianness.  */
  34 #define BTF_MAGIC       0xeb9f
  35 /* Data format version number.  */
  36 #define BTF_VERSION     1
  37
  38 struct btf_header
  39 {
  40   uint16_t magic;       /* Magic number (BTF_MAGIC).  */
  41   uint8_t  version;     /* Data format version (BTF_VERSION).  */
  42   uint8_t  flags;       /* Flags. Currently unused.  */
  43   uint32_t hdr_len;     /* Length of this header (sizeof (struct btf_header)).  */
  44
  45   /* Following offsets are relative to the end of this header.  */
  46   uint32_t type_off;    /* Offset of type section, in bytes.  */
  47   uint32_t type_len;    /* Length of type section, in bytes.  */
  48   uint32_t str_off;     /* Offset of string section, in bytes.  */
  49   uint32_t str_len;     /* Length of string section, in bytes.  */
  50 };
  51
  52 /* Maximum type identifier.  */
  53 #define BTF_MAX_TYPE    0x000fffff
  54 /* Maximum offset into the string section.  */
  55 #define BTF_MAX_NAME_OFFSET     0x00ffffff
  56 /* Maximum number of struct, union, enum members or func args.  */
  57 #define BTF_MAX_VLEN    0xffff
  58
  59 struct btf_type
  60 {
  61   uint32_t name_off;    /* Offset in string section of type name.  */
  62   uint32_t info;        /* Encoded kind, variant length, kind flag:
  63                            - bits  0-15: vlen
  64                            - bits 16-23: unused
  65                            - bits 24-28: kind
  66                            - bits 29-30: unused
  67                            - bit     31: kind_flag
  68                            See accessor macros below.  */
  69
  70   /* SIZE is used by INT, ENUM, STRUCT, UNION, DATASEC kinds.
  71      TYPE is used by PTR, TYPEDEF, VOLATILE, CONST, RESTRICT, FUNC,
  72      FUNC_PROTO and VAR kinds.  */
  73   union
  74   {
  75     uint32_t size;      /* Size of the entire type, in bytes.  */
  76     uint32_t type;      /* A type_id referring to another type.  */
  77   };
  78 };
  79
  80 /* The folloing macros access the information encoded in btf_type.info.  */
  81 /* Type kind. See below.  */
  82 #define BTF_INFO_KIND(info)     (((info) >> 24) & 0x1f)
  83 /* Number of entries of variable length data following certain type kinds.
  84    For example, number of structure members, number of function parameters.  */
  85 #define BTF_INFO_VLEN(info)     ((info) & 0xffff)
  86 /* For BTF_KIND_FWD, 1 if forward to union, 0 if forward to struct.
  87    For BTF_KIND_STRUCT and BTF_KIND_UNION, 1 if the struct/union contains
  88    a bitfield.  */
  89 #define BTF_INFO_KFLAG(info)    ((info) >> 31)
  90
  91 /* Encoding for struct btf_type.info.  */
  92 #define BTF_TYPE_INFO(kind, kflag, vlen) \
  93   ((((kflag) ? 1 : 0 ) << 31) | ((kind) << 24) | ((vlen) & 0xffff))
  94
  95 #define BTF_KIND_UNKN           0       /* Unknown or invalid.  */
  96 #define BTF_KIND_INT            1       /* Integer.  */
  97 #define BTF_KIND_PTR            2       /* Pointer.  */
  98 #define BTF_KIND_ARRAY          3       /* Array.  */
  99 #define BTF_KIND_STRUCT         4       /* Struct.  */
 100 #define BTF_KIND_UNION          5       /* Union.  */
 101 #define BTF_KIND_ENUM           6       /* Enumeration.  */
 102 #define BTF_KIND_FWD            7       /* Forward.  */
 103 #define BTF_KIND_TYPEDEF        8       /* Typedef.  */
 104 #define BTF_KIND_VOLATILE       9       /* Referenced type is volatile.  */
 105 #define BTF_KIND_CONST          10      /* Referenced type is const.  */
 106 #define BTF_KIND_RESTRICT       11      /* Restrict.  */
 107 #define BTF_KIND_FUNC           12      /* Subprogram.  */
 108 #define BTF_KIND_FUNC_PROTO     13      /* Function Prototype.  */
 109 #define BTF_KIND_VAR            14      /* Variable.  */
 110 #define BTF_KIND_DATASEC        15      /* Section such as .bss or .data.  */
 111 #define BTF_KIND_FLOAT          16      /* Floating point.  */
 112 #define BTF_KIND_MAX            BTF_KIND_FLOAT
 113 #define NR_BTF_KINDS            (BTF_KIND_MAX + 1)
 114
 115 /* For some BTF_KINDs, struct btf_type is immediately followed by
 116    additional data describing the type.  */
 117
 118 /* BTF_KIND_INT is followed by a 32-bit word, with the following
 119    bit arrangement.  */
 120 #define BTF_INT_ENCODING(VAL)   (((VAL) & 0x0f000000) >> 24)
 121 #define BTF_INT_OFFSET(VAL)     (((VAL) & 0x00ff0000) >> 16)
 122 #define BTF_INT_BITS(VAL)       ((VAL)  & 0x000000ff)
 123
 124 #define BTF_INT_DATA(encoding, offset, bits) \
 125   ((((encoding) & 0x0f) << 24) | (((offset) & 0xff) << 16) | ((bits) & 0xff))
 126
 127 /* BTF_INT_ENCODING holds the following attribute flags.  */
 128 #define BTF_INT_SIGNED  (1 << 0)
 129 #define BTF_INT_CHAR    (1 << 1)
 130 #define BTF_INT_BOOL    (1 << 2)
 131
 132 /* BTF_KIND_ENUM is followed by VLEN struct btf_enum entries,
 133    which describe the enumerators. Note that BTF currently only
 134    supports signed 32-bit enumerator values.  */
 135 struct btf_enum
 136 {
 137   uint32_t name_off;    /* Offset in string section of enumerator name.  */
 138   int32_t  val;         /* Enumerator value.  */
 139 };
 140
 141 /* BTF_KIND_ARRAY is followed by a single struct btf_array.  */
 142 struct btf_array
 143 {
 144   uint32_t type;        /* Type of array elements.  */
 145   uint32_t index_type;  /* Type of array index.  */
 146   uint32_t nelems;      /* Number of elements. 0 for unsized/variable length.  */
 147 };
 148
 149 /* BTF_KIND_STRUCT and BTF_KIND_UNION are followed by VLEN
 150    struct btf_member.  */
 151 struct btf_member
 152 {
 153   uint32_t name_off;    /* Offset in string section of member name.  */
 154   uint32_t type;        /* Type of member.  */
 155   uint32_t offset;      /* If the type info kind_flag is set, this contains
 156                            both the member bitfield size and bit offset,
 157                            according to the macros below. If kind_flag is not
 158                            set, offset contains only the bit offset (from the
 159                            beginning of the struct).  */
 160 };
 161
 162 /* If struct or union type info kind_flag is set, used to access member
 163    bitfield size from btf_member.offset.  */
 164 #define BTF_MEMBER_BITFIELD_SIZE (val)  ((val) >> 24)
 165 /* If struct or union type info kind_flag is set, used to access member
 166    bit offset from btf_member.offset.  */
 167 #define BTF_MEMBER_BIT_OFFSET (val)     ((val) & 0x00ffffff)
 168
 169 /* BTF_KIND_FUNC_PROTO is followed by VLEN struct btf_param entries, which
 170    describe the types of the function parameters.  */
 171 struct btf_param
 172 {
 173   uint32_t name_off;    /* Offset in string section of parameter name.  */
 174   uint32_t type;        /* Type of parameter.  */
 175 };
 176
 177 /* BTF_KIND_VAR is followed by a single struct btf_var, which describes
 178    information about the variable.  */
 179 struct btf_var
 180 {
 181   uint32_t linkage;     /* Currently only 0=static or 1=global.  */
 182 };
 183
 184 /* BTF_KIND_DATASEC is followed by VLEN struct btf_var_secinfo entries,
 185    which describe all BTF_KIND_VAR types contained in the section.  */
 186 struct btf_var_secinfo
 187 {
 188   uint32_t type;        /* Type of variable.  */
 189   uint32_t offset;      /* In-section offset of variable (in bytes).  */
 190   uint32_t size;        /* Size (in bytes) of variable.  */
 191 };
 192
 193 #ifdef  __cplusplus
 194 }
 195 #endif
 196
 197 #endif /* _BTF_H_ */