1 /* Copyright (C) 2001-2023 Free Software Foundation, Inc.
2
3 This file is part of the GNU C Library.
4
5 The GNU C Library is free software; you can redistribute it and/or
6 modify it under the terms of the GNU Lesser General Public
7 License as published by the Free Software Foundation; either
8 version 2.1 of the License, or (at your option) any later version.
9
10 The GNU C Library is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 Lesser General Public License for more details.
14
15 You should have received a copy of the GNU Lesser General Public
16 License along with the GNU C Library; if not, see
17 <https://www.gnu.org/licenses/>. */
18
19 /* Locate the FDE entry for a given address, using PT_GNU_EH_FRAME ELF
20 segment and dl_iterate_phdr to avoid register/deregister calls at
21 DSO load/unload. */
22
23 #ifdef _LIBC
24 # include <shlib-compat.h>
25 #endif
26
27 #if !defined _LIBC || SHLIB_COMPAT (libc, GLIBC_2_0, GLIBC_2_2_5)
28
29 #include <link.h>
30 #include <stddef.h>
31
32 #define _Unwind_Find_FDE _Unwind_Find_registered_FDE
33
34 #include <unwind-dw2-fde.c>
35
36 #undef _Unwind_Find_FDE
37
38 extern fde * _Unwind_Find_registered_FDE (void *pc,
39 struct dwarf_eh_bases *bases);
40 extern fde * _Unwind_Find_FDE (void *, struct dwarf_eh_bases *);
41
42 struct unw_eh_callback_data
43 {
44 _Unwind_Ptr pc;
45 void *tbase;
46 void *dbase;
47 void *func;
48 fde *ret;
49 };
50
51 struct unw_eh_frame_hdr
52 {
53 unsigned char version;
54 unsigned char eh_frame_ptr_enc;
55 unsigned char fde_count_enc;
56 unsigned char table_enc;
57 };
58
59 /* Like base_of_encoded_value, but take the base from a struct object
60 instead of an _Unwind_Context. */
61
62 static _Unwind_Ptr
63 base_from_cb_data (unsigned char encoding, struct unw_eh_callback_data *data)
64 {
65 if (encoding == DW_EH_PE_omit)
66 return 0;
67
68 switch (encoding & 0x70)
69 {
70 case DW_EH_PE_absptr:
71 case DW_EH_PE_pcrel:
72 case DW_EH_PE_aligned:
73 return 0;
74
75 case DW_EH_PE_textrel:
76 return (_Unwind_Ptr) data->tbase;
77 case DW_EH_PE_datarel:
78 return (_Unwind_Ptr) data->dbase;
79 }
80 abort ();
81 }
82
83 static int
84 _Unwind_IteratePhdrCallback (struct dl_phdr_info *info, size_t size, void *ptr)
85 {
86 struct unw_eh_callback_data *data = (struct unw_eh_callback_data *) ptr;
87 const ElfW(Phdr) *phdr, *p_eh_frame_hdr;
88 const ElfW(Phdr) *p_dynamic __attribute__ ((unused));
89 long n, match;
90 _Unwind_Ptr load_base;
91 const unsigned char *p;
92 const struct unw_eh_frame_hdr *hdr;
93 _Unwind_Ptr eh_frame;
94 struct object ob;
95
96 /* Make sure struct dl_phdr_info is at least as big as we need. */
97 if (size < offsetof (struct dl_phdr_info, dlpi_phnum)
98 + sizeof (info->dlpi_phnum))
99 return -1;
100
101 match = 0;
102 phdr = info->dlpi_phdr;
103 load_base = info->dlpi_addr;
104 p_eh_frame_hdr = NULL;
105 p_dynamic = NULL;
106
107 /* See if PC falls into one of the loaded segments. Find the eh_frame
108 segment at the same time. */
109 for (n = info->dlpi_phnum; --n >= 0; phdr++)
110 {
111 if (phdr->p_type == PT_LOAD)
112 {
113 _Unwind_Ptr vaddr = phdr->p_vaddr + load_base;
114 if (data->pc >= vaddr && data->pc < vaddr + phdr->p_memsz)
115 match = 1;
116 }
117 else if (phdr->p_type == PT_GNU_EH_FRAME)
118 p_eh_frame_hdr = phdr;
119 else if (phdr->p_type == PT_DYNAMIC)
120 p_dynamic = phdr;
121 }
122 if (!match || !p_eh_frame_hdr)
123 return 0;
124
125 /* Read .eh_frame_hdr header. */
126 hdr = (const struct unw_eh_frame_hdr *)
127 (p_eh_frame_hdr->p_vaddr + load_base);
128 if (hdr->version != 1)
129 return 1;
130
131 #ifdef CRT_GET_RFIB_DATA
132 # ifdef __i386__
133 data->dbase = NULL;
134 if (p_dynamic)
135 {
136 /* For dynamically linked executables and shared libraries,
137 DT_PLTGOT is the gp value for that object. */
138 ElfW(Dyn) *dyn = (ElfW(Dyn) *)(p_dynamic->p_vaddr + load_base);
139 for (; dyn->d_tag != DT_NULL ; dyn++)
140 if (dyn->d_tag == DT_PLTGOT)
141 {
142 /* On IA-32, _DYNAMIC is writable and GLIBC has relocated it. */
143 data->dbase = (void *) dyn->d_un.d_ptr;
144 break;
145 }
146 }
147 # else
148 # error What is DW_EH_PE_datarel base on this platform?
149 # endif
150 #endif
151 #ifdef CRT_GET_RFIB_TEXT
152 # error What is DW_EH_PE_textrel base on this platform?
153 #endif
154
155 p = read_encoded_value_with_base (hdr->eh_frame_ptr_enc,
156 base_from_cb_data (hdr->eh_frame_ptr_enc,
157 data),
158 (const unsigned char *) (hdr + 1),
159 &eh_frame);
160
161 /* We require here specific table encoding to speed things up.
162 Also, DW_EH_PE_datarel here means using PT_GNU_EH_FRAME start
163 as base, not the processor specific DW_EH_PE_datarel. */
164 if (hdr->fde_count_enc != DW_EH_PE_omit
165 && hdr->table_enc == (DW_EH_PE_datarel | DW_EH_PE_sdata4))
166 {
167 _Unwind_Ptr fde_count;
168
169 p = read_encoded_value_with_base (hdr->fde_count_enc,
170 base_from_cb_data (hdr->fde_count_enc,
171 data),
172 p, &fde_count);
173 /* Shouldn't happen. */
174 if (fde_count == 0)
175 return 1;
176 if ((((_Unwind_Ptr) p) & 3) == 0)
177 {
178 struct fde_table {
179 signed initial_loc __attribute__ ((mode (SI)));
180 signed fde __attribute__ ((mode (SI)));
181 };
182 const struct fde_table *table = (const struct fde_table *) p;
183 size_t lo, hi, mid;
184 _Unwind_Ptr data_base = (_Unwind_Ptr) hdr;
185 fde *f;
186 unsigned int f_enc, f_enc_size;
187 _Unwind_Ptr range;
188
189 mid = fde_count - 1;
190 if (data->pc < table[0].initial_loc + data_base)
191 return 1;
192 else if (data->pc < table[mid].initial_loc + data_base)
193 {
194 lo = 0;
195 hi = mid;
196
197 while (lo < hi)
198 {
199 mid = (lo + hi) / 2;
200 if (data->pc < table[mid].initial_loc + data_base)
201 hi = mid;
202 else if (data->pc >= table[mid + 1].initial_loc + data_base)
203 lo = mid + 1;
204 else
205 break;
206 }
207
208 if (lo >= hi)
209 __gxx_abort ();
210 }
211
212 f = (fde *) (table[mid].fde + data_base);
213 f_enc = get_fde_encoding (f);
214 f_enc_size = size_of_encoded_value (f_enc);
215 read_encoded_value_with_base (f_enc & 0x0f, 0,
216 &f->pc_begin[f_enc_size], &range);
217 if (data->pc < table[mid].initial_loc + data_base + range)
218 data->ret = f;
219 data->func = (void *) (table[mid].initial_loc + data_base);
220 return 1;
221 }
222 }
223
224 /* We have no sorted search table, so need to go the slow way.
225 As soon as GLIBC will provide API so to notify that a library has been
226 removed, we could cache this (and thus use search_object). */
227 ob.pc_begin = NULL;
228 ob.tbase = data->tbase;
229 ob.dbase = data->dbase;
230 ob.u.single = (fde *) eh_frame;
231 ob.s.i = 0;
232 ob.s.b.mixed_encoding = 1; /* Need to assume worst case. */
233 data->ret = linear_search_fdes (&ob, (fde *) eh_frame, (void *) data->pc);
234 if (data->ret != NULL)
235 {
236 unsigned int encoding = get_fde_encoding (data->ret);
237 _Unwind_Ptr func;
238 read_encoded_value_with_base (encoding,
239 base_from_cb_data (encoding, data),
240 data->ret->pc_begin, &func);
241 data->func = (void *) func;
242 }
243 return 1;
244 }
245
246 # ifdef _LIBC
247 # define dl_iterate_phdr __dl_iterate_phdr
248 # endif
249
250 fde *
251 _Unwind_Find_FDE (void *pc, struct dwarf_eh_bases *bases)
252 {
253 struct unw_eh_callback_data data;
254 fde *ret;
255
256 ret = _Unwind_Find_registered_FDE (pc, bases);
257 if (ret != NULL)
258 return ret;
259
260 data.pc = (_Unwind_Ptr) pc;
261 data.tbase = NULL;
262 data.dbase = NULL;
263 data.func = NULL;
264 data.ret = NULL;
265
266 if (dl_iterate_phdr (_Unwind_IteratePhdrCallback, &data) < 0)
267 return NULL;
268
269 if (data.ret)
270 {
271 bases->tbase = data.tbase;
272 bases->dbase = data.dbase;
273 bases->func = data.func;
274 }
275 return data.ret;
276 }
277
278 #endif