Line data Source code
1 : /*
2 : * Copyright (c) 2017-20 David Lamparter, for NetDEF, Inc.
3 : *
4 : * Permission to use, copy, modify, and distribute this software for any
5 : * purpose with or without fee is hereby granted, provided that the above
6 : * copyright notice and this permission notice appear in all copies.
7 : *
8 : * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
9 : * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
10 : * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
11 : * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
12 : * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
13 : * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
14 : * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
15 : */
16 :
17 : #ifndef _FRR_XREF_H
18 : #define _FRR_XREF_H
19 :
20 : #include <stdint.h>
21 : #include <stdlib.h>
22 : #include <limits.h>
23 : #include <errno.h>
24 : #include "compiler.h"
25 : #include "typesafe.h"
26 :
27 : #ifdef __cplusplus
28 : extern "C" {
29 : #endif
30 :
31 : enum xref_type {
32 : XREFT_NONE = 0,
33 :
34 : XREFT_THREADSCHED = 0x100,
35 :
36 : XREFT_LOGMSG = 0x200,
37 : XREFT_ASSERT = 0x280,
38 :
39 : XREFT_DEFUN = 0x300,
40 : XREFT_INSTALL_ELEMENT = 0x301,
41 : };
42 :
43 : /* struct xref is the "const" part; struct xrefdata is the writable part. */
44 : struct xref;
45 : struct xrefdata;
46 :
47 : struct xref {
48 : /* this may be NULL, depending on the type of the xref.
49 : * if it is NULL, the xref has no unique ID and cannot be accessed
50 : * through that mechanism.
51 : */
52 : struct xrefdata *xrefdata;
53 :
54 : /* type isn't generally needed at runtime */
55 : enum xref_type type;
56 :
57 : /* code location */
58 : int line;
59 : const char *file;
60 : const char *func;
61 :
62 : /* -- 32 bytes (on 64bit) -- */
63 :
64 : /* type-specific bits appended by embedding this struct */
65 : };
66 :
67 : PREDECL_RBTREE_UNIQ(xrefdata_uid);
68 :
69 : struct xrefdata {
70 : /* pointer back to the const part; this will be initialized at
71 : * program startup by xref_block_add(). (Creating structs with
72 : * cyclic pointers to each other is not easily possible for
73 : * function-scoped static variables.)
74 : *
75 : * There is no xrefdata w/o xref, but there are xref w/o xrefdata.
76 : */
77 : const struct xref *xref;
78 :
79 : /* base32(crockford) of unique ID. not all bytes are used, but
80 : * let's pad to 16 for simplicity
81 : */
82 : char uid[16];
83 :
84 : /* hash/uid input
85 : * if hashstr is NULL, no UID is assigned/calculated. Use macro
86 : * string concatenation if multiple values need to be fed in.
87 : * (This is here to not make the UID calculation independent of
88 : * xref type.)
89 : */
90 : const char *hashstr;
91 : uint32_t hashu32[2];
92 :
93 : /* -- 32 bytes (on 64bit) -- */
94 : struct xrefdata_uid_item xui;
95 : };
96 :
97 122994 : static inline int xrefdata_uid_cmp(const struct xrefdata *a,
98 : const struct xrefdata *b)
99 : {
100 122994 : return strcmp(a->uid, b->uid);
101 : }
102 :
103 135852 : DECLARE_RBTREE_UNIQ(xrefdata_uid, struct xrefdata, xui, xrefdata_uid_cmp);
104 : extern struct xrefdata_uid_head xrefdata_uid;
105 :
106 : /* linker "magic" is used to create an array of pointers to struct xref.
107 : * the result is a contiguous block of pointers, each pointing to an xref
108 : * somewhere in the code. The linker gives us start and end pointers, we
109 : * stuff those into the struct below and hook up a constructor to run at
110 : * program startup with the struct passed.
111 : *
112 : * Placing the xrefs themselves into an array doesn't work because they'd
113 : * need to be constant size, but we're embedding struct xref into other
114 : * container structs with extra data. Also this means that external code
115 : * (like the python xref dumper) can safely ignore extra data at the end of
116 : * xrefs without needing to account for size in iterating the array.
117 : *
118 : * If you're curious, this is also how __attribute__((constructor)) (and
119 : * destructor) are implemented - there are 2 arrays, ".init_array" and
120 : * ".fini_array", containing function pointers. The magic turns out to be
121 : * quite mundane, actually ;)
122 : *
123 : * The slightly tricky bit is that this is a per-object (i.e. per shared
124 : * library & daemon) thing and we need a bit of help (in XREF_SETUP) to
125 : * initialize correctly.
126 : */
127 :
128 : struct xref_block {
129 : struct xref_block *next;
130 : const struct xref * const *start;
131 : const struct xref * const *stop;
132 : };
133 :
134 : extern struct xref_block *xref_blocks;
135 : extern void xref_block_add(struct xref_block *block);
136 : extern void xref_gcc_workaround(const struct xref *xref);
137 :
138 : #ifndef HAVE_SECTION_SYMS
139 : /* we have a build system patch to use GNU ld on Solaris; if that doesn't
140 : * work we end up on Solaris ld which doesn't support the section start/end
141 : * symbols.
142 : */
143 : #define XREF_SETUP() \
144 : CPP_NOTICE("Missing linker support for section arrays. Solaris ld?")
145 : #else
146 : /* the actual symbols that the linker provides for us. Note these are
147 : * _symbols_ referring to the actual section start/end, i.e. they are very
148 : * much NOT _pointers_, rather the symbol *value* is the pointer. Declaring
149 : * them as size-1 arrays is the "best" / "right" thing.
150 : */
151 : extern const struct xref * const __start_xref_array[1] DSO_LOCAL;
152 : extern const struct xref * const __stop_xref_array[1] DSO_LOCAL;
153 :
154 : #if defined(__has_feature)
155 : #if __has_feature(address_sanitizer)
156 : /* no redzone around each of the xref_p please, we're building an array out
157 : * of variables here. kinda breaks things if there's redzones between each
158 : * array item.
159 : */
160 : #define xref_array_attr used, section("xref_array"), no_sanitize("address")
161 : #endif
162 : #endif
163 : #ifndef xref_array_attr
164 : #define xref_array_attr used, section("xref_array")
165 : #endif
166 :
167 : /* this macro is invoked once for each standalone DSO through
168 : * FRR_MODULE_SETUP \
169 : * }-> FRR_COREMOD_SETUP -> XREF_SETUP
170 : * FRR_DAEMON_INFO /
171 : */
172 : #define XREF_SETUP() \
173 : static const struct xref _dummy_xref = { \
174 : /* .xrefdata = */ NULL, \
175 : /* .type = */ XREFT_NONE, \
176 : /* .line = */ __LINE__, \
177 : /* .file = */ __FILE__, \
178 : /* .func = */ "dummy", \
179 : }; \
180 : static const struct xref * const _dummy_xref_p \
181 : __attribute__((xref_array_attr)) = &_dummy_xref; \
182 : static void __attribute__((used, _CONSTRUCTOR(1100))) \
183 : _xref_init(void) { \
184 : static struct xref_block _xref_block = { \
185 : .next = NULL, \
186 : .start = __start_xref_array, \
187 : .stop = __stop_xref_array, \
188 : }; \
189 : xref_block_add(&_xref_block); \
190 : } \
191 : asm(XREF_NOTE); \
192 : MACRO_REQUIRE_SEMICOLON() /* end */
193 :
194 : /* the following blurb emits an ELF note indicating start and end of the xref
195 : * array in the binary. This is technically the "correct" entry point for
196 : * external tools reading xrefs out of an ELF shared library or executable.
197 : *
198 : * right now, the extraction tools use the section header for "xref_array"
199 : * instead; however, section headers are technically not necessarily preserved
200 : * for fully linked libraries or executables. (In practice they are only
201 : * stripped by obfuscation tools.)
202 : *
203 : * conversely, for reading xrefs out of a single relocatable object file (e.g.
204 : * bar.o), section headers are the right thing to look at since the note is
205 : * only emitted for the final binary once.
206 : *
207 : * FRR itself does not need this note to operate correctly, so if you have
208 : * some build issue with it just add -DFRR_XREF_NO_NOTE to your build flags
209 : * to disable it.
210 : */
211 : #if defined(FRR_XREF_NO_NOTE) || defined(__mips64)
212 : #define XREF_NOTE ""
213 :
214 : /* mips64 note: MIPS64 (regardless of endianness, both mips64 & mips64el)
215 : * does not have a 64-bit PC-relative relocation type. Unfortunately, a
216 : * 64-bit PC-relative relocation is exactly what the below asm magic emits.
217 : * Therefore, the xref ELF note is permanently disabled on MIPS64.
218 : *
219 : * For some context, refer to https://reviews.llvm.org/D80390
220 : *
221 : * As noted above, xref extraction still works through the section header
222 : * path, so no functionality is lost.
223 : */
224 : #else
225 :
226 : #if __SIZEOF_POINTER__ == 4
227 : #define _NOTE_2PTRSIZE "8"
228 : #define _NOTE_PTR ".long"
229 : #elif __SIZEOF_POINTER__ == 8
230 : #define _NOTE_2PTRSIZE "16"
231 : #define _NOTE_PTR ".quad"
232 : #else
233 : #error unsupported pointer size
234 : #endif
235 :
236 : #ifdef __arm__
237 : # define asmspecial "%"
238 : #else
239 : # define asmspecial "@"
240 : #endif
241 :
242 : #define XREF_NOTE \
243 : "" "\n"\
244 : " .type _frr_xref_note," asmspecial "object" "\n"\
245 : " .pushsection .note.FRR,\"a\"," asmspecial "note" "\n"\
246 : " .p2align 2" "\n"\
247 : "_frr_xref_note:" "\n"\
248 : " .long 9" "\n"\
249 : " .long " _NOTE_2PTRSIZE "\n"\
250 : " .ascii \"XREF\"" "\n"\
251 : " .ascii \"FRRouting\\0\\0\\0\"" "\n"\
252 : " " _NOTE_PTR " __start_xref_array-." "\n"\
253 : " " _NOTE_PTR " __stop_xref_array-." "\n"\
254 : " .size _frr_xref_note, .-_frr_xref_note" "\n"\
255 : " .popsection" "\n"\
256 : "" "\n"\
257 : /* end */
258 : #endif
259 :
260 : #endif /* HAVE_SECTION_SYMS */
261 :
262 : /* emit the array entry / pointer to xref */
263 : #if defined(__clang__) || !defined(__cplusplus)
264 : #define XREF_LINK(dst) \
265 : static const struct xref * const NAMECTR(xref_p_) \
266 : __attribute__((xref_array_attr)) \
267 : = &(dst) \
268 : /* end */
269 :
270 : #else /* GCC && C++ */
271 : /* workaround for GCC bug 41091 (dated 2009), added in 2021...
272 : *
273 : * this breaks extraction of xrefs with xrelfo.py (because the xref_array
274 : * entry will be missing), but provides full runtime functionality. To get
275 : * the proper list of xrefs from C++ code, build with clang...
276 : */
277 : struct _xref_p {
278 : const struct xref * const ptr;
279 :
280 : _xref_p(const struct xref *_ptr) : ptr(_ptr)
281 : {
282 : xref_gcc_workaround(_ptr);
283 : }
284 : };
285 :
286 : #define XREF_LINK(dst) \
287 : static const struct _xref_p __attribute__((used)) \
288 : NAMECTR(xref_p_)(&(dst)) \
289 : /* end */
290 : #endif
291 :
292 : /* initializer for a "struct xref" */
293 : #define XREF_INIT(type_, xrefdata_, func_) \
294 : { \
295 : /* .xrefdata = */ (xrefdata_), \
296 : /* .type = */ (type_), \
297 : /* .line = */ __LINE__, \
298 : /* .file = */ __FILE__, \
299 : /* .func = */ func_, \
300 : } \
301 : /* end */
302 :
303 : /* use with XREF_INIT when outside of a function, i.e. no __func__ */
304 : #define XREF_NO_FUNC "<global>"
305 :
306 : #ifdef __cplusplus
307 : }
308 : #endif
309 :
310 : #endif /* _FRR_XREF_H */
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