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8bdabb37 | 1 | /* BPF Compile Once - Run Everywhere (CO-RE) support. |
7adcbafe | 2 | Copyright (C) 2021-2022 Free Software Foundation, Inc. |
8bdabb37 DF |
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 | |
12 | WITHOUT ANY WARRANTY; without even the implied warranty of | |
13 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU | |
14 | General Public 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 | #define IN_TARGET_CODE 1 | |
21 | ||
22 | #include "config.h" | |
23 | #include "system.h" | |
24 | #include "coretypes.h" | |
25 | #include "target.h" | |
26 | #include "memmodel.h" | |
27 | #include "tm_p.h" | |
28 | #include "output.h" | |
29 | #include "dwarf2asm.h" | |
30 | #include "ctfc.h" | |
31 | #include "btf.h" | |
32 | #include "rtl.h" | |
33 | ||
34 | #include "coreout.h" | |
35 | ||
36 | /* This file contains data structures and routines for construction and output | |
37 | of BPF Compile Once - Run Everywhere (BPF CO-RE) information. | |
38 | ||
39 | eBPF programs written in C usually include Linux kernel headers, so that | |
40 | they may interact with kernel data structures in a useful way. This | |
41 | intrudces two major portability issues: | |
42 | ||
43 | 1. Kernel data structures regularly change, with fields added, moved or | |
44 | deleted between versions. An eBPF program cannot in general be expected | |
45 | to run on any systems which does not share an identical kernel version to | |
46 | the system on which it was compiled. | |
47 | ||
48 | 2. Included kernel headers (and used data structures) may be internal, not | |
49 | exposed in an userspace API, and therefore target-specific. An eBPF | |
50 | program compiled on an x86_64 machine will include x86_64 kernel headers. | |
51 | The resulting program may not run well (or at all) in machines of | |
52 | another architecture. | |
53 | ||
54 | BPF CO-RE is designed to solve the first issue by leveraging the BPF loader | |
55 | to adjust references to kernel data structures made by the program as-needed | |
56 | according to versions of structures actually present on the host kernel. | |
57 | ||
58 | To achieve this, additional information is placed in a ".BTF.ext" section. | |
59 | This information tells the loader which references will require adjusting, | |
60 | and how to perform each necessary adjustment. | |
61 | ||
62 | For any access to a data structure which may require load-time adjustment, | |
63 | the following information is recorded (making up a CO-RE relocation record): | |
64 | - The BTF type ID of the outermost structure which is accessed. | |
65 | - An access string encoding the accessed member via a series of member and | |
66 | array indexes. These indexes are used to look up detailed BTF information | |
67 | about the member. | |
68 | - The offset of the appropriate instruction to patch in the BPF program. | |
69 | - An integer specifying what kind of relocation to perform. | |
70 | ||
71 | A CO-RE-capable BPF loader reads this information together with the BTF | |
72 | information of the program, compares it against BTF information of the host | |
73 | kernel, and determines the appropriate way to patch the specified | |
74 | instruction. | |
75 | ||
76 | Once all CO-RE relocations are resolved, the program is loaded and verified | |
77 | as usual. The process can be summarized with the following diagram: | |
78 | ||
79 | +------------+ | |
80 | | C compiler | | |
81 | +-----+------+ | |
82 | | BPF + BTF + CO-RE relocations | |
83 | v | |
84 | +------------+ | |
85 | +--->| BPF loader | | |
86 | | +-----+------+ | |
87 | | | BPF (adapted) | |
88 | BTF | v | |
89 | | +------------+ | |
90 | +----+ Kernel | | |
91 | +------------+ | |
92 | ||
93 | Note that a single ELF object may contain multiple eBPF programs. As a | |
94 | result, a single .BTF.ext section can contain CO-RE relocations for multiple | |
95 | programs in distinct sections. */ | |
96 | ||
97 | /* Internal representation of a BPF CO-RE relocation record. */ | |
98 | ||
99 | typedef struct GTY (()) bpf_core_reloc { | |
100 | unsigned int bpfcr_type; /* BTF type ID of container. */ | |
101 | unsigned int bpfcr_astr_off; /* Offset of access string in .BTF | |
102 | string table. */ | |
103 | rtx_code_label * bpfcr_insn_label; /* RTX label attached to instruction | |
104 | to patch. */ | |
105 | enum btf_core_reloc_kind bpfcr_kind; /* Kind of relocation to perform. */ | |
106 | } bpf_core_reloc_t; | |
107 | ||
108 | typedef bpf_core_reloc_t * bpf_core_reloc_ref; | |
109 | ||
110 | /* Internal representation of a CO-RE relocation (sub)section of the | |
111 | .BTF.ext information. One such section is generated for each ELF section | |
112 | in the output object having relocations that a BPF loader must resolve. */ | |
113 | ||
114 | typedef struct GTY (()) bpf_core_section { | |
115 | /* Name of ELF section to which these CO-RE relocations apply. */ | |
116 | const char * name; | |
117 | ||
118 | /* Offset of section name in .BTF string table. */ | |
119 | uint32_t name_offset; | |
120 | ||
121 | /* Relocations in the section. */ | |
122 | vec <bpf_core_reloc_ref, va_gc> * GTY (()) relocs; | |
123 | } bpf_core_section_t; | |
124 | ||
125 | typedef bpf_core_section_t * bpf_core_section_ref; | |
126 | ||
127 | /* BTF.ext debug info section. */ | |
128 | ||
129 | static GTY (()) section * btf_ext_info_section; | |
130 | ||
131 | static int btf_ext_label_num; | |
132 | ||
133 | #ifndef BTF_EXT_INFO_SECTION_NAME | |
134 | #define BTF_EXT_INFO_SECTION_NAME ".BTF.ext" | |
135 | #endif | |
136 | ||
137 | #define BTF_EXT_INFO_SECTION_FLAGS (SECTION_DEBUG) | |
138 | ||
139 | #define MAX_BTF_EXT_LABEL_BYTES 40 | |
140 | ||
141 | static char btf_ext_info_section_label[MAX_BTF_EXT_LABEL_BYTES]; | |
142 | ||
143 | #ifndef BTF_EXT_INFO_SECTION_LABEL | |
144 | #define BTF_EXT_INFO_SECTION_LABEL "Lbtfext" | |
145 | #endif | |
146 | ||
147 | static GTY (()) vec<bpf_core_section_ref, va_gc> *bpf_core_sections; | |
148 | ||
149 | ||
150 | /* Create a new BPF CO-RE relocation record, and add it to the appropriate | |
151 | CO-RE section. */ | |
152 | ||
153 | void | |
154 | bpf_core_reloc_add (const tree type, const char * section_name, | |
155 | vec<unsigned int> *accessors, rtx_code_label *label) | |
156 | { | |
157 | char buf[40]; | |
158 | unsigned int i, n = 0; | |
159 | ||
160 | /* A valid CO-RE access must have at least one accessor. */ | |
161 | if (accessors->length () < 1) | |
162 | return; | |
163 | ||
164 | for (i = 0; i < accessors->length () - 1; i++) | |
165 | n += snprintf (buf + n, sizeof (buf) - n, "%u:", (*accessors)[i]); | |
166 | snprintf (buf + n, sizeof (buf) - n, "%u", (*accessors)[i]); | |
167 | ||
168 | bpf_core_reloc_ref bpfcr = ggc_cleared_alloc<bpf_core_reloc_t> (); | |
169 | ctf_container_ref ctfc = ctf_get_tu_ctfc (); | |
170 | ||
171 | /* Buffer the access string in the auxiliary strtab. Since the two string | |
172 | tables are concatenated, add the length of the first to the offset. */ | |
173 | size_t strtab_len = ctfc_get_strtab_len (ctfc, CTF_STRTAB); | |
174 | ctf_add_string (ctfc, buf, &(bpfcr->bpfcr_astr_off), CTF_AUX_STRTAB); | |
175 | bpfcr->bpfcr_astr_off += strtab_len; | |
176 | ||
177 | bpfcr->bpfcr_type = get_btf_id (ctf_lookup_tree_type (ctfc, type)); | |
178 | bpfcr->bpfcr_insn_label = label; | |
179 | bpfcr->bpfcr_kind = BPF_RELO_FIELD_BYTE_OFFSET; | |
180 | ||
181 | /* Add the CO-RE reloc to the appropriate section. */ | |
182 | bpf_core_section_ref sec; | |
183 | FOR_EACH_VEC_ELT (*bpf_core_sections, i, sec) | |
184 | if (strcmp (sec->name, section_name) == 0) | |
185 | { | |
186 | vec_safe_push (sec->relocs, bpfcr); | |
187 | return; | |
188 | } | |
189 | ||
190 | /* If the CO-RE section does not yet exist, create it. */ | |
191 | sec = ggc_cleared_alloc<bpf_core_section_t> (); | |
192 | ||
193 | ctf_add_string (ctfc, section_name, &sec->name_offset, CTF_AUX_STRTAB); | |
194 | sec->name_offset += strtab_len; | |
195 | if (strcmp (section_name, "")) | |
196 | ctfc->ctfc_aux_strlen += strlen (section_name) + 1; | |
197 | ||
198 | sec->name = section_name; | |
199 | vec_alloc (sec->relocs, 1); | |
200 | vec_safe_push (sec->relocs, bpfcr); | |
201 | ||
202 | vec_safe_push (bpf_core_sections, sec); | |
203 | } | |
204 | ||
205 | /* Return the 0-based index of the field NODE in its containing struct or union | |
206 | type. */ | |
207 | ||
208 | int | |
209 | bpf_core_get_sou_member_index (ctf_container_ref ctfc, const tree node) | |
210 | { | |
211 | if (TREE_CODE (node) == FIELD_DECL) | |
212 | { | |
213 | const tree container = DECL_CONTEXT (node); | |
214 | const char * name = IDENTIFIER_POINTER (DECL_NAME (node)); | |
215 | ||
216 | /* Lookup the CTF type info for the containing type. */ | |
217 | dw_die_ref die = lookup_type_die (container); | |
218 | if (die == NULL) | |
219 | return -1; | |
220 | ||
221 | ctf_dtdef_ref dtd = ctf_dtd_lookup (ctfc, die); | |
222 | if (dtd == NULL) | |
223 | return -1; | |
224 | ||
225 | unsigned int kind = CTF_V2_INFO_KIND (dtd->dtd_data.ctti_info); | |
226 | if (kind != CTF_K_STRUCT && kind != CTF_K_UNION) | |
227 | return -1; | |
228 | ||
229 | int i = 0; | |
230 | ctf_dmdef_t * dmd; | |
231 | for (dmd = dtd->dtd_u.dtu_members; | |
232 | dmd != NULL; dmd = (ctf_dmdef_t *) ctf_dmd_list_next (dmd)) | |
233 | { | |
234 | if (get_btf_id (dmd->dmd_type) > BTF_MAX_TYPE) | |
235 | continue; | |
236 | if (strcmp (dmd->dmd_name, name) == 0) | |
237 | return i; | |
238 | i++; | |
239 | } | |
240 | } | |
241 | return -1; | |
242 | } | |
243 | ||
244 | /* Compute and output the header of a .BTF.ext debug info section. */ | |
245 | ||
246 | static void | |
247 | output_btfext_header (void) | |
248 | { | |
249 | switch_to_section (btf_ext_info_section); | |
250 | ASM_OUTPUT_LABEL (asm_out_file, btf_ext_info_section_label); | |
251 | ||
252 | dw2_asm_output_data (2, BTF_MAGIC, "btf_magic"); | |
253 | dw2_asm_output_data (1, BTF_VERSION, "btfext_version"); | |
254 | dw2_asm_output_data (1, 0, "btfext_flags"); | |
255 | dw2_asm_output_data (4, sizeof (struct btf_ext_header), "btfext_hdr_len"); | |
256 | ||
257 | uint32_t func_info_off = 0, func_info_len = 0; | |
258 | uint32_t line_info_off = 0, line_info_len = 0; | |
259 | uint32_t core_relo_off = 0, core_relo_len = 0; | |
260 | ||
261 | /* Header core_relo_len is the sum total length in bytes of all CO-RE | |
262 | relocation sections. */ | |
263 | size_t i; | |
264 | bpf_core_section_ref sec; | |
265 | core_relo_len += vec_safe_length (bpf_core_sections) | |
266 | * sizeof (struct btf_ext_section_header); | |
267 | ||
268 | FOR_EACH_VEC_ELT (*bpf_core_sections, i, sec) | |
269 | core_relo_len += | |
270 | vec_safe_length (sec->relocs) * sizeof (struct btf_ext_reloc); | |
271 | ||
272 | dw2_asm_output_data (4, func_info_off, "func_info_offset"); | |
273 | dw2_asm_output_data (4, func_info_len, "func_info_len"); | |
274 | ||
275 | dw2_asm_output_data (4, line_info_off, "line_info_offset"); | |
276 | dw2_asm_output_data (4, line_info_len, "line_info_len"); | |
277 | ||
278 | dw2_asm_output_data (4, core_relo_off, "core_relo_offset"); | |
279 | dw2_asm_output_data (4, core_relo_len, "core_relo_len"); | |
280 | } | |
281 | ||
282 | /* Output a single CO-RE relocation record. */ | |
283 | ||
284 | static void | |
285 | output_asm_btfext_core_reloc (bpf_core_reloc_ref bpfcr) | |
286 | { | |
287 | dw2_assemble_integer (4, gen_rtx_LABEL_REF (Pmode, bpfcr->bpfcr_insn_label)); | |
288 | fprintf (asm_out_file, "\t%s bpfcr_insn\n", ASM_COMMENT_START); | |
289 | ||
290 | dw2_asm_output_data (4, bpfcr->bpfcr_type, "bpfcr_type"); | |
291 | dw2_asm_output_data (4, bpfcr->bpfcr_astr_off, "bpfcr_astr_off"); | |
292 | dw2_asm_output_data (4, bpfcr->bpfcr_kind, "bpfcr_kind"); | |
293 | } | |
294 | ||
295 | /* Output all CO-RE relocation records for a section. */ | |
296 | ||
297 | static void | |
298 | output_btfext_core_relocs (bpf_core_section_ref sec) | |
299 | { | |
300 | size_t i; | |
301 | bpf_core_reloc_ref bpfcr; | |
302 | FOR_EACH_VEC_ELT (*(sec->relocs), i, bpfcr) | |
303 | output_asm_btfext_core_reloc (bpfcr); | |
304 | } | |
305 | ||
306 | /* Output all CO-RE relocation sections. */ | |
307 | ||
308 | static void | |
309 | output_btfext_core_sections (void) | |
310 | { | |
311 | size_t i; | |
312 | bpf_core_section_ref sec; | |
313 | FOR_EACH_VEC_ELT (*bpf_core_sections, i, sec) | |
314 | { | |
315 | /* BTF Ext section info. */ | |
316 | dw2_asm_output_data (4, sizeof (struct btf_ext_reloc), | |
317 | "btfext_secinfo_rec_size"); | |
318 | ||
319 | /* Section name offset, refers to the offset of a string with the name of | |
320 | the section to which these CORE relocations refer, e.g. '.text'. | |
321 | The string is buffered in the BTF strings table. */ | |
322 | dw2_asm_output_data (4, sec->name_offset, "btfext_secinfo_sec_name_off"); | |
323 | dw2_asm_output_data (4, vec_safe_length (sec->relocs), | |
324 | "btfext_secinfo_num_recs"); | |
325 | ||
326 | output_btfext_core_relocs (sec); | |
327 | } | |
328 | } | |
329 | ||
330 | /* Initialize sections, labels, and data structures for BTF.ext output. */ | |
331 | ||
332 | void | |
333 | btf_ext_init (void) | |
334 | { | |
335 | btf_ext_info_section = get_section (BTF_EXT_INFO_SECTION_NAME, | |
336 | BTF_EXT_INFO_SECTION_FLAGS, NULL); | |
337 | ||
338 | ASM_GENERATE_INTERNAL_LABEL (btf_ext_info_section_label, | |
339 | BTF_EXT_INFO_SECTION_LABEL, | |
340 | btf_ext_label_num++); | |
341 | ||
342 | vec_alloc (bpf_core_sections, 1); | |
343 | } | |
344 | ||
345 | /* Output the entire .BTF.ext section. */ | |
346 | ||
347 | void | |
348 | btf_ext_output (void) | |
349 | { | |
350 | output_btfext_header (); | |
351 | output_btfext_core_sections (); | |
352 | ||
353 | bpf_core_sections = NULL; | |
354 | } | |
355 | ||
356 | #include "gt-coreout.h" |