include/sframe.h

   1 /* SFrame format description.
   2    Copyright (C) 2022-2024 Free Software Foundation, Inc.
   3
   4    This file is part of libsframe.
   5
   6    libsframe is free software; you can redistribute it and/or modify it
   7    under the terms of the GNU General Public License as published by the Free
   8    Software Foundation; either version 3, or (at your option) any later
   9    version.
  10
  11    This program is distributed in the hope that it will be useful, but
  12    WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
  14    See the GNU General Public License for more details.
  15
  16    You should have received a copy of the GNU General Public License
  17    along with this program; see the file COPYING.  If not see
  18    <http://www.gnu.org/licenses/>.  */
  19
  20 #ifndef _SFRAME_H
  21 #define _SFRAME_H
  22
  23 #include <sys/types.h>
  24 #include <limits.h>
  25 #include <stdint.h>
  26
  27 #include "ansidecl.h"
  28
  29 #ifdef  __cplusplus
  30 extern "C"
  31 {
  32 #endif
  33
  34 /* SFrame format.
  35
  36    SFrame format is a simple format to represent the information needed
  37    for generating vanilla backtraces.  SFrame format keeps track of the
  38    minimal necessary information needed for stack tracing:
  39      - Canonical Frame Address (CFA)
  40      - Frame Pointer (FP)
  41      - Return Address (RA)
  42
  43    The SFrame section itself has the following structure:
  44
  45        +--------+------------+---------+
  46        |  file  |  function  | frame   |
  47        | header | descriptor |  row    |
  48        |        |   entries  | entries |
  49        +--------+------------+---------+
  50
  51    The file header stores a magic number and version information, flags, and
  52    the byte offset of each of the sections relative to the end of the header
  53    itself.  The file header also specifies the total number of Function
  54    Descriptor Entries, Frame Row Entries and length of the FRE sub-section.
  55
  56    Following the header is a list of Function Descriptor Entries (FDEs).
  57    This list may be sorted if the flags in the file header indicate it to be
  58    so.  The sort order, if applicable, is the order of functions in the
  59    .text.* sections in the resulting binary artifact.  Each Function
  60    Descriptor Entry specifies the start PC of a function, the size in bytes
  61    of the function and an offset to its first Frame Row Entry (FRE).  Each FDE
  62    additionally also specifies the type of FRE it uses to encode the stack
  63    trace information.
  64
  65    Next, the SFrame Frame Row Entry sub-section is a list of variable size
  66    records.  Each entry represents stack trace information for a set of PCs
  67    of the function.  A singular Frame Row Entry is a self-sufficient record
  68    which contains information on how to generate stack trace from the
  69    applicable set of PCs.
  70
  71    */
  72
  73
  74 /* SFrame format versions.  */
  75 #define SFRAME_VERSION_1        1
  76 #define SFRAME_VERSION_2        2
  77 /* SFrame magic number.  */
  78 #define SFRAME_MAGIC            0xdee2
  79 /* Current version of SFrame format.  */
  80 #define SFRAME_VERSION  SFRAME_VERSION_2
  81
  82 /* Various flags for SFrame.  */
  83
  84 /* Function Descriptor Entries are sorted on PC.  */
  85 #define SFRAME_F_FDE_SORTED     0x1
  86 /* Functions preserve frame pointer.  */
  87 #define SFRAME_F_FRAME_POINTER 0x2
  88
  89 #define SFRAME_CFA_FIXED_FP_INVALID 0
  90 #define SFRAME_CFA_FIXED_RA_INVALID 0
  91
  92 /* Supported ABIs/Arch.  */
  93 #define SFRAME_ABI_AARCH64_ENDIAN_BIG      1 /* AARCH64 big endian.  */
  94 #define SFRAME_ABI_AARCH64_ENDIAN_LITTLE   2 /* AARCH64 little endian.  */
  95 #define SFRAME_ABI_AMD64_ENDIAN_LITTLE     3 /* AMD64 little endian.  */
  96
  97 /* SFrame FRE types.  */
  98 #define SFRAME_FRE_TYPE_ADDR1   0
  99 #define SFRAME_FRE_TYPE_ADDR2   1
 100 #define SFRAME_FRE_TYPE_ADDR4   2
 101
 102 /* SFrame Function Descriptor Entry types.
 103
 104    The SFrame format has two possible representations for functions.  The
 105    choice of which type to use is made according to the instruction patterns
 106    in the relevant program stub.
 107
 108    An SFrame FDE of type SFRAME_FDE_TYPE_PCINC is an indication
 109    that the PCs in the FREs should be treated as increments in bytes.  This is
 110    used for a bulk of the executable code of a program, which contains
 111    instructions with no specific pattern.
 112
 113    An SFrame FDE of type SFRAME_FDE_TYPE_PCMASK is an indication
 114    that the PCs in the FREs should be treated as masks.  This type is useful
 115    for the cases when a small pattern of instructions in a program stub is
 116    repeatedly to cover a specific functionality.  Typical usescases are pltN
 117    entries, trampolines etc.  */
 118
 119 /* Unwinders perform a (PC >= FRE_START_ADDR) to look up a matching FRE.  */
 120 #define SFRAME_FDE_TYPE_PCINC   0
 121 /* Unwinders perform a (PC % REP_BLOCK_SIZE >= FRE_START_ADDR) to look up a
 122    matching FRE.  */
 123 #define SFRAME_FDE_TYPE_PCMASK  1
 124
 125 typedef struct sframe_preamble
 126 {
 127   uint16_t sfp_magic;   /* Magic number (SFRAME_MAGIC).  */
 128   uint8_t sfp_version;  /* Data format version number (SFRAME_VERSION).  */
 129   uint8_t sfp_flags;    /* Flags.  */
 130 } ATTRIBUTE_PACKED sframe_preamble;
 131
 132 typedef struct sframe_header
 133 {
 134   sframe_preamble sfh_preamble;
 135   /* Information about the arch (endianness) and ABI.  */
 136   uint8_t sfh_abi_arch;
 137   /* Offset for the Frame Pointer (FP) from CFA may be fixed for some
 138      ABIs (e.g, in AMD64 when -fno-omit-frame-pointer is used).  When fixed,
 139      this field specifies the fixed stack frame offset and the individual
 140      FREs do not need to track it.  When not fixed, it is set to
 141      SFRAME_CFA_FIXED_FP_INVALID, and the individual FREs may provide
 142      the applicable stack frame offset, if any.  */
 143   int8_t sfh_cfa_fixed_fp_offset;
 144   /* Offset for the Return Address from CFA is fixed for some ABIs
 145      (e.g., AMD64 has it as CFA-8).  When fixed, the header specifies the
 146      fixed stack frame offset and the individual FREs do not track it.  When
 147      not fixed, it is set to SFRAME_CFA_FIXED_RA_INVALID, and individual
 148      FREs provide the applicable stack frame offset, if any.  */
 149   int8_t sfh_cfa_fixed_ra_offset;
 150   /* Number of bytes making up the auxiliary header, if any.
 151      Some ABI/arch, in the future, may use this space for extending the
 152      information in SFrame header.  Auxiliary header is contained in
 153      bytes sequentially following the sframe_header.  */
 154   uint8_t sfh_auxhdr_len;
 155   /* Number of SFrame FDEs in this SFrame section.  */
 156   uint32_t sfh_num_fdes;
 157   /* Number of SFrame Frame Row Entries.  */
 158   uint32_t sfh_num_fres;
 159   /* Number of bytes in the SFrame Frame Row Entry section. */
 160   uint32_t sfh_fre_len;
 161   /* Offset of SFrame Function Descriptor Entry section.  */
 162   uint32_t sfh_fdeoff;
 163   /* Offset of SFrame Frame Row Entry section.  */
 164   uint32_t sfh_freoff;
 165 } ATTRIBUTE_PACKED sframe_header;
 166
 167 #define SFRAME_V1_HDR_SIZE(sframe_hdr)  \
 168   ((sizeof (sframe_header) + (sframe_hdr).sfh_auxhdr_len))
 169
 170 /* Two possible keys for executable (instruction) pointers signing.  */
 171 #define SFRAME_AARCH64_PAUTH_KEY_A    0 /* Key A.  */
 172 #define SFRAME_AARCH64_PAUTH_KEY_B    1 /* Key B.  */
 173
 174 typedef struct sframe_func_desc_entry
 175 {
 176   /* Function start address.  Encoded as a signed offset, relative to the
 177      beginning of the current FDE.  */
 178   int32_t sfde_func_start_address;
 179   /* Size of the function in bytes.  */
 180   uint32_t sfde_func_size;
 181   /* Offset of the first SFrame Frame Row Entry of the function, relative to the
 182      beginning of the SFrame Frame Row Entry sub-section.  */
 183   uint32_t sfde_func_start_fre_off;
 184   /* Number of frame row entries for the function.  */
 185   uint32_t sfde_func_num_fres;
 186   /* Additional information for stack tracing from the function:
 187      - 4-bits: Identify the FRE type used for the function.
 188      - 1-bit: Identify the FDE type of the function - mask or inc.
 189      - 1-bit: PAC authorization A/B key (aarch64).
 190      - 2-bits: Unused.
 191      ------------------------------------------------------------------------
 192      |     Unused    |  PAC auth A/B key (aarch64) |  FDE type |   FRE type   |
 193      |               |        Unused (amd64)       |           |              |
 194      ------------------------------------------------------------------------
 195      8               6                             5           4              0     */
 196   uint8_t sfde_func_info;
 197   /* Size of the block of repeating insns.  Used for SFrame FDEs of type
 198      SFRAME_FDE_TYPE_PCMASK.  */
 199   uint8_t sfde_func_rep_size;
 200   uint16_t sfde_func_padding2;
 201 } ATTRIBUTE_PACKED sframe_func_desc_entry;
 202
 203 /* Macros to compose and decompose function info in FDE.  */
 204
 205 /* Note: Set PAC auth key to SFRAME_AARCH64_PAUTH_KEY_A by default.  */
 206 #define SFRAME_V1_FUNC_INFO(fde_type, fre_enc_type) \
 207   (((SFRAME_AARCH64_PAUTH_KEY_A & 0x1) << 5) | \
 208    (((fde_type) & 0x1) << 4) | ((fre_enc_type) & 0xf))
 209
 210 #define SFRAME_V1_FUNC_FRE_TYPE(data)     ((data) & 0xf)
 211 #define SFRAME_V1_FUNC_FDE_TYPE(data)     (((data) >> 4) & 0x1)
 212 #define SFRAME_V1_FUNC_PAUTH_KEY(data)    (((data) >> 5) & 0x1)
 213
 214 /* Set the pauth key as indicated.  */
 215 #define SFRAME_V1_FUNC_INFO_UPDATE_PAUTH_KEY(pauth_key, fde_info) \
 216   ((((pauth_key) & 0x1) << 5) | ((fde_info) & 0xdf))
 217
 218 /* Size of stack frame offsets in an SFrame Frame Row Entry.  A single
 219    SFrame FRE has all offsets of the same size.  Offset size may vary
 220    across frame row entries.  */
 221 #define SFRAME_FRE_OFFSET_1B      0
 222 #define SFRAME_FRE_OFFSET_2B      1
 223 #define SFRAME_FRE_OFFSET_4B      2
 224
 225 /* An SFrame Frame Row Entry can be SP or FP based.  */
 226 #define SFRAME_BASE_REG_FP      0
 227 #define SFRAME_BASE_REG_SP      1
 228
 229 /* The index at which a specific offset is presented in the variable length
 230    bytes of an FRE.  */
 231 #define SFRAME_FRE_CFA_OFFSET_IDX   0
 232 /* The RA stack offset, if present, will always be at index 1 in the variable
 233    length bytes of the FRE.  */
 234 #define SFRAME_FRE_RA_OFFSET_IDX    1
 235 /* The FP stack offset may appear at offset 1 or 2, depending on the ABI as RA
 236    may or may not be tracked.  */
 237 #define SFRAME_FRE_FP_OFFSET_IDX    2
 238
 239 typedef struct sframe_fre_info
 240 {
 241   /* Information about
 242      - 1 bit: base reg for CFA
 243      - 4 bits: Number of offsets (N).  A value of upto 3 is allowed to track
 244      all three of CFA, FP and RA (fixed implicit order).
 245      - 2 bits: information about size of the offsets (S) in bytes.
 246      Valid values are SFRAME_FRE_OFFSET_1B, SFRAME_FRE_OFFSET_2B,
 247      SFRAME_FRE_OFFSET_4B
 248      - 1 bit: Mangled RA state bit (aarch64 only).
 249      ----------------------------------------------------------------------------------
 250      | Mangled-RA (aarch64) |  Size of offsets   |   Number of offsets    |   base_reg |
 251      |  Unused (amd64)      |                    |                        |            |
 252      ----------------------------------------------------------------------------------
 253      8                     7                    5                        1            0
 254
 255      */
 256   uint8_t fre_info;
 257 } sframe_fre_info;
 258
 259 /* Macros to compose and decompose FRE info.  */
 260
 261 /* Note: Set mangled_ra_p to zero by default.  */
 262 #define SFRAME_V1_FRE_INFO(base_reg_id, offset_num, offset_size) \
 263   (((0 & 0x1) << 7) | (((offset_size) & 0x3) << 5) | \
 264    (((offset_num) & 0xf) << 1) | ((base_reg_id) & 0x1))
 265
 266 /* Set the mangled_ra_p bit as indicated.  */
 267 #define SFRAME_V1_FRE_INFO_UPDATE_MANGLED_RA_P(mangled_ra_p, fre_info) \
 268   ((((mangled_ra_p) & 0x1) << 7) | ((fre_info) & 0x7f))
 269
 270 #define SFRAME_V1_FRE_CFA_BASE_REG_ID(data)       ((data) & 0x1)
 271 #define SFRAME_V1_FRE_OFFSET_COUNT(data)          (((data) >> 1) & 0xf)
 272 #define SFRAME_V1_FRE_OFFSET_SIZE(data)           (((data) >> 5) & 0x3)
 273 #define SFRAME_V1_FRE_MANGLED_RA_P(data)          (((data) >> 7) & 0x1)
 274
 275 /* SFrame Frame Row Entry definitions.
 276
 277    Used for both AMD64 and AARCH64.
 278
 279    An SFrame Frame Row Entry is a self-sufficient record which contains
 280    information on how to generate the stack trace for the specified range of
 281    PCs.  Each SFrame Frame Row Entry is followed by S*N bytes, where:
 282      S is the size of the stack frame offset for the FRE, and
 283      N is the number of stack frame offsets in the FRE
 284
 285    The interpretation of FRE stack offsets is ABI-specific:
 286
 287    AMD64:
 288      offset1 (interpreted as CFA = BASE_REG + offset1)
 289       if FP is being tracked
 290         offset2 (intrepreted as FP = CFA + offset2)
 291       fi
 292
 293     AARCH64:
 294      offset1 (interpreted as CFA = BASE_REG + offset1)
 295      if FP is being tracked (in other words, if frame record created)
 296        offset2 (interpreted as RA = CFA + offset2)
 297        offset3 (intrepreted as FP = CFA + offset3)
 298      fi
 299      Note that in AAPCS64, a frame record, if created, will save both FP and
 300      LR on stack.
 301 */
 302
 303 /* Used when SFRAME_FRE_TYPE_ADDR1 is specified as FRE type.  */
 304 typedef struct sframe_frame_row_entry_addr1
 305 {
 306   /* Start address of the frame row entry.  Encoded as an 1-byte unsigned
 307      offset, relative to the start address of the function.  */
 308   uint8_t sfre_start_address;
 309   sframe_fre_info sfre_info;
 310 } ATTRIBUTE_PACKED sframe_frame_row_entry_addr1;
 311
 312 /* Upper limit of start address in sframe_frame_row_entry_addr1
 313    is 0x100 (not inclusive).  */
 314 #define SFRAME_FRE_TYPE_ADDR1_LIMIT   \
 315   (1ULL << ((SFRAME_FRE_TYPE_ADDR1 + 1) * 8))
 316
 317 /* Used when SFRAME_FRE_TYPE_ADDR2 is specified as FRE type.  */
 318 typedef struct sframe_frame_row_entry_addr2
 319 {
 320   /* Start address of the frame row entry.  Encoded as an 2-byte unsigned
 321      offset, relative to the start address of the function.  */
 322   uint16_t sfre_start_address;
 323   sframe_fre_info sfre_info;
 324 } ATTRIBUTE_PACKED sframe_frame_row_entry_addr2;
 325
 326 /* Upper limit of start address in sframe_frame_row_entry_addr2
 327    is 0x10000 (not inclusive).  */
 328 #define SFRAME_FRE_TYPE_ADDR2_LIMIT   \
 329   (1ULL << ((SFRAME_FRE_TYPE_ADDR2 * 2) * 8))
 330
 331 /* Used when SFRAME_FRE_TYPE_ADDR4 is specified as FRE type.  */
 332 typedef struct sframe_frame_row_entry_addr4
 333 {
 334   /* Start address of the frame row entry.  Encoded as a 4-byte unsigned
 335      offset, relative to the start address of the function.  */
 336   uint32_t sfre_start_address;
 337   sframe_fre_info sfre_info;
 338 } ATTRIBUTE_PACKED sframe_frame_row_entry_addr4;
 339
 340 /* Upper limit of start address in sframe_frame_row_entry_addr2
 341    is 0x100000000 (not inclusive).  */
 342 #define SFRAME_FRE_TYPE_ADDR4_LIMIT   \
 343   (1ULL << ((SFRAME_FRE_TYPE_ADDR4 * 2) * 8))
 344
 345 #ifdef  __cplusplus
 346 }
 347 #endif
 348
 349 #endif                          /* _SFRAME_H */