1 /* SFrame format description.
2 Copyright (C) 2022-2023 Free Software Foundation, Inc.
4 This file is part of libsframe.
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
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.
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/>. */
23 #include <sys/types.h>
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)
43 The SFrame section itself has the following structure:
45 +--------+------------+---------+
46 | file | function | frame |
47 | header | descriptor | row |
48 | | entries | entries |
49 +--------+------------+---------+
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.
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
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.
74 /* SFrame format versions. */
75 #define SFRAME_VERSION_1 1
76 /* SFrame magic number. */
77 #define SFRAME_MAGIC 0xdee2
78 /* Current version of SFrame format. */
79 #define SFRAME_VERSION SFRAME_VERSION_1
81 /* Various flags for SFrame. */
83 /* Function Descriptor Entries are sorted on PC. */
84 #define SFRAME_F_FDE_SORTED 0x1
85 /* Functions preserve frame pointer. */
86 #define SFRAME_F_FRAME_POINTER 0x2
88 #define SFRAME_CFA_FIXED_FP_INVALID 0
89 #define SFRAME_CFA_FIXED_RA_INVALID 0
91 /* Supported ABIs/Arch. */
92 #define SFRAME_ABI_AARCH64_ENDIAN_BIG 1 /* AARCH64 big endian. */
93 #define SFRAME_ABI_AARCH64_ENDIAN_LITTLE 2 /* AARCH64 little endian. */
94 #define SFRAME_ABI_AMD64_ENDIAN_LITTLE 3 /* AMD64 little endian. */
96 /* SFrame FRE types. */
97 #define SFRAME_FRE_TYPE_ADDR1 0
98 #define SFRAME_FRE_TYPE_ADDR2 1
99 #define SFRAME_FRE_TYPE_ADDR4 2
101 /* SFrame Function Descriptor Entry types.
103 The SFrame format has two possible representations for functions. The
104 choice of which type to use is made according to the instruction patterns
105 in the relevant program stub.
107 An SFrame FDE of type SFRAME_FDE_TYPE_PCINC is an indication
108 that the PCs in the FREs should be treated as increments in bytes. This is
109 used for a bulk of the executable code of a program, which contains
110 instructions with no specific pattern.
112 An SFrame FDE of type SFRAME_FDE_TYPE_PCMASK is an indication
113 that the PCs in the FREs should be treated as masks. This type is useful
114 for the cases when a small pattern of instructions in a program stub is
115 repeatedly to cover a specific functionality. Typical usescases are pltN
116 entries, trampolines etc. */
118 /* Unwinders perform a (PC >= FRE_START_ADDR) to look up a matching FRE. */
119 #define SFRAME_FDE_TYPE_PCINC 0
120 /* Unwinders perform a (PC & FRE_START_ADDR_AS_MASK >= FRE_START_ADDR_AS_MASK)
121 to look up a matching FRE. */
122 #define SFRAME_FDE_TYPE_PCMASK 1
124 typedef struct sframe_preamble
126 uint16_t sfp_magic
; /* Magic number (SFRAME_MAGIC). */
127 uint8_t sfp_version
; /* Data format version number (SFRAME_VERSION). */
128 uint8_t sfp_flags
; /* Flags. */
129 } ATTRIBUTE_PACKED sframe_preamble
;
131 typedef struct sframe_header
133 sframe_preamble sfh_preamble
;
134 /* Information about the arch (endianness) and ABI. */
135 uint8_t sfh_abi_arch
;
136 /* Offset for the Frame Pointer (FP) from CFA may be fixed for some
137 ABIs (e.g, in AMD64 when -fno-omit-frame-pointer is used). When fixed,
138 this field specifies the fixed stack frame offset and the individual
139 FREs do not need to track it. When not fixed, it is set to
140 SFRAME_CFA_FIXED_FP_INVALID, and the individual FREs may provide
141 the applicable stack frame offset, if any. */
142 int8_t sfh_cfa_fixed_fp_offset
;
143 /* Offset for the Return Address from CFA is fixed for some ABIs
144 (e.g., AMD64 has it as CFA-8). When fixed, the header specifies the
145 fixed stack frame offset and the individual FREs do not track it. When
146 not fixed, it is set to SFRAME_CFA_FIXED_RA_INVALID, and individual
147 FREs provide the applicable stack frame offset, if any. */
148 int8_t sfh_cfa_fixed_ra_offset
;
149 /* Number of bytes making up the auxilliary header, if any.
150 Some ABI/arch, in the future, may use this space for extending the
151 information in SFrame header. Auxilliary header is contained in
152 bytes sequentially following the sframe_header. */
153 uint8_t sfh_auxhdr_len
;
154 /* Number of SFrame FDEs in this SFrame section. */
155 uint32_t sfh_num_fdes
;
156 /* Number of SFrame Frame Row Entries. */
157 uint32_t sfh_num_fres
;
158 /* Number of bytes in the SFrame Frame Row Entry section. */
159 uint32_t sfh_fre_len
;
160 /* Offset of SFrame Function Descriptor Entry section. */
162 /* Offset of SFrame Frame Row Entry section. */
164 } ATTRIBUTE_PACKED sframe_header
;
166 #define SFRAME_V1_HDR_SIZE(sframe_hdr) \
167 ((sizeof (sframe_header) + (sframe_hdr).sfh_auxhdr_len))
169 /* Two possible keys for executable (instruction) pointers signing. */
170 #define SFRAME_AARCH64_PAUTH_KEY_A 0 /* Key A. */
171 #define SFRAME_AARCH64_PAUTH_KEY_B 1 /* Key B. */
173 typedef struct sframe_func_desc_entry
175 /* Function start address. Encoded as a signed offset, relative to the
176 beginning of the current FDE. */
177 int32_t sfde_func_start_address
;
178 /* Size of the function in bytes. */
179 uint32_t sfde_func_size
;
180 /* Offset of the first SFrame Frame Row Entry of the function, relative to the
181 beginning of the SFrame Frame Row Entry sub-section. */
182 uint32_t sfde_func_start_fre_off
;
183 /* Number of frame row entries for the function. */
184 uint32_t sfde_func_num_fres
;
185 /* Additional information for stack tracing from the function:
186 - 4-bits: Identify the FRE type used for the function.
187 - 1-bit: Identify the FDE type of the function - mask or inc.
188 - 1-bit: PAC authorization A/B key (aarch64).
190 ------------------------------------------------------------------------
191 | Unused | PAC auth A/B key (aarch64) | FDE type | FRE type |
192 | | Unused (amd64) | | |
193 ------------------------------------------------------------------------
195 uint8_t sfde_func_info
;
196 } ATTRIBUTE_PACKED sframe_func_desc_entry
;
198 /* Macros to compose and decompose function info in FDE. */
200 /* Note: Set PAC auth key to SFRAME_AARCH64_PAUTH_KEY_A by default. */
201 #define SFRAME_V1_FUNC_INFO(fde_type, fre_enc_type) \
202 (((SFRAME_AARCH64_PAUTH_KEY_A & 0x1) << 5) | \
203 (((fde_type) & 0x1) << 4) | ((fre_enc_type) & 0xf))
205 #define SFRAME_V1_FUNC_FRE_TYPE(data) ((data) & 0xf)
206 #define SFRAME_V1_FUNC_FDE_TYPE(data) (((data) >> 4) & 0x1)
207 #define SFRAME_V1_FUNC_PAUTH_KEY(data) (((data) >> 5) & 0x1)
209 /* Set the pauth key as indicated. */
210 #define SFRAME_V1_FUNC_INFO_UPDATE_PAUTH_KEY(pauth_key, fde_info) \
211 ((((pauth_key) & 0x1) << 5) | ((fde_info) & 0xdf))
213 /* Size of stack frame offsets in an SFrame Frame Row Entry. A single
214 SFrame FRE has all offsets of the same size. Offset size may vary
215 across frame row entries. */
216 #define SFRAME_FRE_OFFSET_1B 0
217 #define SFRAME_FRE_OFFSET_2B 1
218 #define SFRAME_FRE_OFFSET_4B 2
220 /* An SFrame Frame Row Entry can be SP or FP based. */
221 #define SFRAME_BASE_REG_FP 0
222 #define SFRAME_BASE_REG_SP 1
224 /* The index at which a specific offset is presented in the variable length
226 #define SFRAME_FRE_CFA_OFFSET_IDX 0
227 /* The RA stack offset, if present, will always be at index 1 in the variable
228 length bytes of the FRE. */
229 #define SFRAME_FRE_RA_OFFSET_IDX 1
230 /* The FP stack offset may appear at offset 1 or 2, depending on the ABI as RA
231 may or may not be tracked. */
232 #define SFRAME_FRE_FP_OFFSET_IDX 2
234 typedef struct sframe_fre_info
237 - 1 bit: base reg for CFA
238 - 4 bits: Number of offsets (N). A value of upto 3 is allowed to track
239 all three of CFA, FP and RA (fixed implicit order).
240 - 2 bits: information about size of the offsets (S) in bytes.
241 Valid values are SFRAME_FRE_OFFSET_1B, SFRAME_FRE_OFFSET_2B,
243 - 1 bit: Mangled RA state bit (aarch64 only).
244 ----------------------------------------------------------------------------------
245 | Mangled-RA (aarch64) | Size of offsets | Number of offsets | base_reg |
246 | Unused (amd64) | | | |
247 ----------------------------------------------------------------------------------
254 /* Macros to compose and decompose FRE info. */
256 /* Note: Set mangled_ra_p to zero by default. */
257 #define SFRAME_V1_FRE_INFO(base_reg_id, offset_num, offset_size) \
258 (((0 & 0x1) << 7) | (((offset_size) & 0x3) << 5) | \
259 (((offset_num) & 0xf) << 1) | ((base_reg_id) & 0x1))
261 /* Set the mangled_ra_p bit as indicated. */
262 #define SFRAME_V1_FRE_INFO_UPDATE_MANGLED_RA_P(mangled_ra_p, fre_info) \
263 ((((mangled_ra_p) & 0x1) << 7) | ((fre_info) & 0x7f))
265 #define SFRAME_V1_FRE_CFA_BASE_REG_ID(data) ((data) & 0x1)
266 #define SFRAME_V1_FRE_OFFSET_COUNT(data) (((data) >> 1) & 0xf)
267 #define SFRAME_V1_FRE_OFFSET_SIZE(data) (((data) >> 5) & 0x3)
268 #define SFRAME_V1_FRE_MANGLED_RA_P(data) (((data) >> 7) & 0x1)
270 /* SFrame Frame Row Entry definitions.
272 Used for both AMD64 and AARCH64.
274 An SFrame Frame Row Entry is a self-sufficient record which contains
275 information on how to generate the stack trace for the specified range of
276 PCs. Each SFrame Frame Row Entry is followed by S*N bytes, where:
277 S is the size of the stack frame offset for the FRE, and
278 N is the number of stack frame offsets in the FRE
280 The offsets are interpreted in order as follows:
282 offset1 (interpreted as CFA = BASE_REG + offset1)
284 if RA is being tracked
285 offset2 (interpreted as RA = CFA + offset2)
286 if FP is being tracked
287 offset3 (intrepreted as FP = CFA + offset2)
290 if FP is being tracked
291 offset2 (intrepreted as FP = CFA + offset2)
296 /* Used when SFRAME_FRE_TYPE_ADDR1 is specified as FRE type. */
297 typedef struct sframe_frame_row_entry_addr1
299 /* Start address of the frame row entry. Encoded as an 1-byte unsigned
300 offset, relative to the start address of the function. */
301 uint8_t sfre_start_address
;
302 sframe_fre_info sfre_info
;
303 } ATTRIBUTE_PACKED sframe_frame_row_entry_addr1
;
305 /* Upper limit of start address in sframe_frame_row_entry_addr1
306 is 0x100 (not inclusive). */
307 #define SFRAME_FRE_TYPE_ADDR1_LIMIT \
308 (1ULL << ((SFRAME_FRE_TYPE_ADDR1 + 1) * 8))
310 /* Used when SFRAME_FRE_TYPE_ADDR2 is specified as FRE type. */
311 typedef struct sframe_frame_row_entry_addr2
313 /* Start address of the frame row entry. Encoded as an 2-byte unsigned
314 offset, relative to the start address of the function. */
315 uint16_t sfre_start_address
;
316 sframe_fre_info sfre_info
;
317 } ATTRIBUTE_PACKED sframe_frame_row_entry_addr2
;
319 /* Upper limit of start address in sframe_frame_row_entry_addr2
320 is 0x10000 (not inclusive). */
321 #define SFRAME_FRE_TYPE_ADDR2_LIMIT \
322 (1ULL << ((SFRAME_FRE_TYPE_ADDR2 * 2) * 8))
324 /* Used when SFRAME_FRE_TYPE_ADDR4 is specified as FRE type. */
325 typedef struct sframe_frame_row_entry_addr4
327 /* Start address of the frame row entry. Encoded as a 4-byte unsigned
328 offset, relative to the start address of the function. */
329 uint32_t sfre_start_address
;
330 sframe_fre_info sfre_info
;
331 } ATTRIBUTE_PACKED sframe_frame_row_entry_addr4
;
333 /* Upper limit of start address in sframe_frame_row_entry_addr2
334 is 0x100000000 (not inclusive). */
335 #define SFRAME_FRE_TYPE_ADDR4_LIMIT \
336 (1ULL << ((SFRAME_FRE_TYPE_ADDR4 * 2) * 8))
342 #endif /* _SFRAME_H */