1 /* Machine-dependent ELF dynamic relocation inline functions. i386 version.
2 Copyright (C) 1995-2023 Free Software Foundation, Inc.
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 #ifndef dl_machine_h
20 #define dl_machine_h
21
22 #define ELF_MACHINE_NAME "i386"
23
24 #include <assert.h>
25 #include <sys/param.h>
26 #include <sysdep.h>
27 #include <tls.h>
28 #include <dl-tlsdesc.h>
29 #include <dl-static-tls.h>
30 #include <dl-machine-rel.h>
31
32 /* Return nonzero iff ELF header is compatible with the running host. */
33 static inline int __attribute__ ((unused))
34 elf_machine_matches_host (const Elf32_Ehdr *ehdr)
35 {
36 return ehdr->e_machine == EM_386;
37 }
38
39
40 /* Return the run-time load address of the shared object. */
41 static inline Elf32_Addr __attribute__ ((unused))
42 elf_machine_load_address (void)
43 {
44 extern const Elf32_Ehdr __ehdr_start attribute_hidden;
45 return (Elf32_Addr) &__ehdr_start;
46 }
47
48 /* Return the link-time address of _DYNAMIC. */
49 static inline Elf32_Addr __attribute__ ((unused))
50 elf_machine_dynamic (void)
51 {
52 extern Elf32_Dyn _DYNAMIC[] attribute_hidden;
53 return (Elf32_Addr) _DYNAMIC - elf_machine_load_address ();
54 }
55
56 /* Set up the loaded object described by L so its unrelocated PLT
57 entries will jump to the on-demand fixup code in dl-runtime.c. */
58
59 static inline int __attribute__ ((unused, always_inline))
60 elf_machine_runtime_setup (struct link_map *l, struct r_scope_elem *scope[],
61 int lazy, int profile)
62 {
63 Elf32_Addr *got;
64 extern void _dl_runtime_resolve (Elf32_Word) attribute_hidden;
65 extern void _dl_runtime_profile (Elf32_Word) attribute_hidden;
66 extern void _dl_runtime_resolve_shstk (Elf32_Word) attribute_hidden;
67 extern void _dl_runtime_profile_shstk (Elf32_Word) attribute_hidden;
68 /* Check if SHSTK is enabled by kernel. */
69 bool shstk_enabled
70 = (GL(dl_x86_feature_1) & GNU_PROPERTY_X86_FEATURE_1_SHSTK) != 0;
71
72 if (l->l_info[DT_JMPREL] && lazy)
73 {
74 /* The GOT entries for functions in the PLT have not yet been filled
75 in. Their initial contents will arrange when called to push an
76 offset into the .rel.plt section, push _GLOBAL_OFFSET_TABLE_[1],
77 and then jump to _GLOBAL_OFFSET_TABLE[2]. */
78 got = (Elf32_Addr *) D_PTR (l, l_info[DT_PLTGOT]);
79 /* If a library is prelinked but we have to relocate anyway,
80 we have to be able to undo the prelinking of .got.plt.
81 The prelinker saved us here address of .plt + 0x16. */
82 if (got[1])
83 {
84 l->l_mach.plt = got[1] + l->l_addr;
85 l->l_mach.gotplt = (Elf32_Addr) &got[3];
86 }
87 got[1] = (Elf32_Addr) l; /* Identify this shared object. */
88
89 /* The got[2] entry contains the address of a function which gets
90 called to get the address of a so far unresolved function and
91 jump to it. The profiling extension of the dynamic linker allows
92 to intercept the calls to collect information. In this case we
93 don't store the address in the GOT so that all future calls also
94 end in this function. */
95 if (__glibc_unlikely (profile))
96 {
97 got[2] = (shstk_enabled
98 ? (Elf32_Addr) &_dl_runtime_profile_shstk
99 : (Elf32_Addr) &_dl_runtime_profile);
100
101 if (GLRO(dl_profile) != NULL
102 && _dl_name_match_p (GLRO(dl_profile), l))
103 /* This is the object we are looking for. Say that we really
104 want profiling and the timers are started. */
105 GL(dl_profile_map) = l;
106 }
107 else
108 /* This function will get called to fix up the GOT entry indicated by
109 the offset on the stack, and then jump to the resolved address. */
110 got[2] = (shstk_enabled
111 ? (Elf32_Addr) &_dl_runtime_resolve_shstk
112 : (Elf32_Addr) &_dl_runtime_resolve);
113 }
114
115 return lazy;
116 }
117
118 /* Mask identifying addresses reserved for the user program,
119 where the dynamic linker should not map anything. */
120 #define ELF_MACHINE_USER_ADDRESS_MASK 0xf8000000UL
121
122 /* Initial entry point code for the dynamic linker.
123 The C function `_dl_start' is the real entry point;
124 its return value is the user program's entry point. */
125
126 #define RTLD_START asm ("\n\
127 .text\n\
128 .align 16\n\
129 0: movl (%esp), %ebx\n\
130 ret\n\
131 .align 16\n\
132 .globl _start\n\
133 .globl _dl_start_user\n\
134 _start:\n\
135 movl %esp, %eax\n\
136 subl $12, %esp\n\
137 pushl %eax\n\
138 call _dl_start\n\
139 addl $16, %esp\n\
140 _dl_start_user:\n\
141 # Save the user entry point address in %edi.\n\
142 movl %eax, %edi\n\
143 # Point %ebx at the GOT.\n\
144 call 0b\n\
145 addl $_GLOBAL_OFFSET_TABLE_, %ebx\n\
146 # Read the original argument count.\n\
147 movl (%esp), %edx\n\
148 # The special initializer gets called with the stack just\n\
149 # as the application's entry point will see it; it can\n\
150 # switch stacks if it moves these contents over.\n\
151 " RTLD_START_SPECIAL_INIT "\n\
152 # Load the parameters again.\n\
153 # (eax, edx, ecx, esi) = (_dl_loaded, argc, argv, envp)\n\
154 movl _rtld_local@GOTOFF(%ebx), %eax\n\
155 leal 8(%esp,%edx,4), %esi\n\
156 leal 4(%esp), %ecx\n\
157 movl %esp, %ebp\n\
158 # Make sure _dl_init is run with 16 byte aligned stack.\n\
159 andl $-16, %esp\n\
160 subl $12, %esp\n\
161 pushl %ebp\n\
162 # Arguments for _dl_init.\n\
163 pushl %esi\n\
164 pushl %ecx\n\
165 pushl %edx\n\
166 pushl %eax\n\
167 # Clear %ebp, so that even constructors have terminated backchain.\n\
168 xorl %ebp, %ebp\n\
169 # Call the function to run the initializers.\n\
170 call _dl_init\n\
171 # Pass our finalizer function to the user in %edx, as per ELF ABI.\n\
172 leal _dl_fini@GOTOFF(%ebx), %edx\n\
173 # Restore %esp _start expects.\n\
174 movl 16(%esp), %esp\n\
175 # Jump to the user's entry point.\n\
176 jmp *%edi\n\
177 .previous\n\
178 ");
179
180 #ifndef RTLD_START_SPECIAL_INIT
181 # define RTLD_START_SPECIAL_INIT /* nothing */
182 #endif
183
184 /* ELF_RTYPE_CLASS_PLT iff TYPE describes relocation of a PLT entry or
185 TLS variable, so undefined references should not be allowed to
186 define the value.
187 ELF_RTYPE_CLASS_COPY iff TYPE should not be allowed to resolve to one
188 of the main executable's symbols, as for a COPY reloc. */
189 # define elf_machine_type_class(type) \
190 ((((type) == R_386_JMP_SLOT || (type) == R_386_TLS_DTPMOD32 \
191 || (type) == R_386_TLS_DTPOFF32 || (type) == R_386_TLS_TPOFF32 \
192 || (type) == R_386_TLS_TPOFF || (type) == R_386_TLS_DESC) \
193 * ELF_RTYPE_CLASS_PLT) \
194 | (((type) == R_386_COPY) * ELF_RTYPE_CLASS_COPY))
195
196 /* A reloc type used for ld.so cmdline arg lookups to reject PLT entries. */
197 #define ELF_MACHINE_JMP_SLOT R_386_JMP_SLOT
198
199 /* We define an initialization functions. This is called very early in
200 _dl_sysdep_start. */
201 #define DL_PLATFORM_INIT dl_platform_init ()
202
203 static inline void __attribute__ ((unused))
204 dl_platform_init (void)
205 {
206 #if IS_IN (rtld)
207 /* _dl_x86_init_cpu_features is a wrapper for init_cpu_features which
208 has been called early from __libc_start_main in static executable. */
209 _dl_x86_init_cpu_features ();
210 #else
211 if (GLRO(dl_platform) != NULL && *GLRO(dl_platform) == '\0')
212 /* Avoid an empty string which would disturb us. */
213 GLRO(dl_platform) = NULL;
214 #endif
215 }
216
217 static inline Elf32_Addr
218 elf_machine_fixup_plt (struct link_map *map, lookup_t t,
219 const ElfW(Sym) *refsym, const ElfW(Sym) *sym,
220 const Elf32_Rel *reloc,
221 Elf32_Addr *reloc_addr, Elf32_Addr value)
222 {
223 return *reloc_addr = value;
224 }
225
226 /* Return the final value of a plt relocation. */
227 static inline Elf32_Addr
228 elf_machine_plt_value (struct link_map *map, const Elf32_Rel *reloc,
229 Elf32_Addr value)
230 {
231 return value;
232 }
233
234
235 /* Names of the architecture-specific auditing callback functions. */
236 #define ARCH_LA_PLTENTER i86_gnu_pltenter
237 #define ARCH_LA_PLTEXIT i86_gnu_pltexit
238
239 #endif /* !dl_machine_h */
240
241 #ifdef RESOLVE_MAP
242
243 /* Perform the relocation specified by RELOC and SYM (which is fully resolved).
244 MAP is the object containing the reloc. */
245
246 static inline void
247 __attribute ((always_inline))
248 elf_machine_rel (struct link_map *map, struct r_scope_elem *scope[],
249 const Elf32_Rel *reloc,
250 const Elf32_Sym *sym, const struct r_found_version *version,
251 void *const reloc_addr_arg, int skip_ifunc)
252 {
253 Elf32_Addr *const reloc_addr = reloc_addr_arg;
254 const unsigned int r_type = ELF32_R_TYPE (reloc->r_info);
255
256 # if !defined RTLD_BOOTSTRAP
257 if (__glibc_unlikely (r_type == R_386_RELATIVE))
258 *reloc_addr += map->l_addr;
259 # ifndef RTLD_BOOTSTRAP
260 else if (__glibc_unlikely (r_type == R_386_NONE))
261 return;
262 # endif
263 else
264 # endif /* !RTLD_BOOTSTRAP */
265 {
266 # ifndef RTLD_BOOTSTRAP
267 const Elf32_Sym *const refsym = sym;
268 # endif
269 struct link_map *sym_map = RESOLVE_MAP (map, scope, &sym, version,
270 r_type);
271 Elf32_Addr value = SYMBOL_ADDRESS (sym_map, sym, true);
272
273 if (sym != NULL
274 && __glibc_unlikely (ELFW(ST_TYPE) (sym->st_info) == STT_GNU_IFUNC)
275 && __glibc_likely (sym->st_shndx != SHN_UNDEF)
276 && __glibc_likely (!skip_ifunc))
277 {
278 # ifndef RTLD_BOOTSTRAP
279 if (sym_map != map
280 && !sym_map->l_relocated)
281 {
282 const char *strtab
283 = (const char *) D_PTR (map, l_info[DT_STRTAB]);
284 if (sym_map->l_type == lt_executable)
285 _dl_fatal_printf ("\
286 %s: IFUNC symbol '%s' referenced in '%s' is defined in the executable \
287 and creates an unsatisfiable circular dependency.\n",
288 RTLD_PROGNAME, strtab + refsym->st_name,
289 map->l_name);
290 else
291 _dl_error_printf ("\
292 %s: Relink `%s' with `%s' for IFUNC symbol `%s'\n",
293 RTLD_PROGNAME, map->l_name,
294 sym_map->l_name,
295 strtab + refsym->st_name);
296 }
297 # endif
298 value = ((Elf32_Addr (*) (void)) value) ();
299 }
300
301 switch (r_type)
302 {
303 # ifndef RTLD_BOOTSTRAP
304 case R_386_SIZE32:
305 /* Set to symbol size plus addend. */
306 *reloc_addr += sym->st_size;
307 break;
308 # endif
309 case R_386_GLOB_DAT:
310 case R_386_JMP_SLOT:
311 *reloc_addr = value;
312 break;
313
314 case R_386_TLS_DTPMOD32:
315 # ifdef RTLD_BOOTSTRAP
316 /* During startup the dynamic linker is always the module
317 with index 1.
318 XXX If this relocation is necessary move before RESOLVE
319 call. */
320 *reloc_addr = 1;
321 # else
322 /* Get the information from the link map returned by the
323 resolv function. */
324 if (sym_map != NULL)
325 *reloc_addr = sym_map->l_tls_modid;
326 # endif
327 break;
328 case R_386_TLS_DTPOFF32:
329 # ifndef RTLD_BOOTSTRAP
330 /* During relocation all TLS symbols are defined and used.
331 Therefore the offset is already correct. */
332 if (sym != NULL)
333 *reloc_addr = sym->st_value;
334 # endif
335 break;
336 case R_386_TLS_DESC:
337 {
338 struct tlsdesc volatile *td =
339 (struct tlsdesc volatile *)reloc_addr;
340
341 # ifndef RTLD_BOOTSTRAP
342 if (! sym)
343 td->entry = _dl_tlsdesc_undefweak;
344 else
345 # endif
346 {
347 # ifndef RTLD_BOOTSTRAP
348 # ifndef SHARED
349 CHECK_STATIC_TLS (map, sym_map);
350 # else
351 if (!TRY_STATIC_TLS (map, sym_map))
352 {
353 td->arg = _dl_make_tlsdesc_dynamic
354 (sym_map, sym->st_value + (ElfW(Word))td->arg);
355 td->entry = _dl_tlsdesc_dynamic;
356 }
357 else
358 # endif
359 # endif
360 {
361 td->arg = (void*)(sym->st_value - sym_map->l_tls_offset
362 + (ElfW(Word))td->arg);
363 td->entry = _dl_tlsdesc_return;
364 }
365 }
366 break;
367 }
368 case R_386_TLS_TPOFF32:
369 /* The offset is positive, backward from the thread pointer. */
370 # ifdef RTLD_BOOTSTRAP
371 *reloc_addr += map->l_tls_offset - sym->st_value;
372 # else
373 /* We know the offset of object the symbol is contained in.
374 It is a positive value which will be subtracted from the
375 thread pointer. To get the variable position in the TLS
376 block we subtract the offset from that of the TLS block. */
377 if (sym != NULL)
378 {
379 CHECK_STATIC_TLS (map, sym_map);
380 *reloc_addr += sym_map->l_tls_offset - sym->st_value;
381 }
382 # endif
383 break;
384 case R_386_TLS_TPOFF:
385 /* The offset is negative, forward from the thread pointer. */
386 # ifdef RTLD_BOOTSTRAP
387 *reloc_addr += sym->st_value - map->l_tls_offset;
388 # else
389 /* We know the offset of object the symbol is contained in.
390 It is a negative value which will be added to the
391 thread pointer. */
392 if (sym != NULL)
393 {
394 CHECK_STATIC_TLS (map, sym_map);
395 *reloc_addr += sym->st_value - sym_map->l_tls_offset;
396 }
397 # endif
398 break;
399
400 # ifndef RTLD_BOOTSTRAP
401 case R_386_32:
402 *reloc_addr += value;
403 break;
404 case R_386_PC32:
405 *reloc_addr += (value - (Elf32_Addr) reloc_addr);
406 break;
407 case R_386_COPY:
408 if (sym == NULL)
409 /* This can happen in trace mode if an object could not be
410 found. */
411 break;
412 if (__glibc_unlikely (sym->st_size > refsym->st_size)
413 || (__glibc_unlikely(sym->st_size < refsym->st_size)
414 && GLRO(dl_verbose)))
415 {
416 const char *strtab;
417
418 strtab = (const char *) D_PTR (map, l_info[DT_STRTAB]);
419 _dl_error_printf ("\
420 %s: Symbol `%s' has different size in shared object, consider re-linking\n",
421 RTLD_PROGNAME, strtab + refsym->st_name);
422 }
423 memcpy (reloc_addr_arg, (void *) value,
424 MIN (sym->st_size, refsym->st_size));
425 break;
426 case R_386_IRELATIVE:
427 value = map->l_addr + *reloc_addr;
428 if (__glibc_likely (!skip_ifunc))
429 value = ((Elf32_Addr (*) (void)) value) ();
430 *reloc_addr = value;
431 break;
432 default:
433 _dl_reloc_bad_type (map, r_type, 0);
434 break;
435 # endif /* !RTLD_BOOTSTRAP */
436 }
437 }
438 }
439
440
441 static inline void
442 __attribute ((always_inline))
443 elf_machine_rel_relative (Elf32_Addr l_addr, const Elf32_Rel *reloc,
444 void *const reloc_addr_arg)
445 {
446 Elf32_Addr *const reloc_addr = reloc_addr_arg;
447 assert (ELF32_R_TYPE (reloc->r_info) == R_386_RELATIVE);
448 *reloc_addr += l_addr;
449 }
450
451 # ifndef RTLD_BOOTSTRAP
452 static inline void
453 __attribute__ ((always_inline))
454 elf_machine_rela_relative (Elf32_Addr l_addr, const Elf32_Rela *reloc,
455 void *const reloc_addr_arg)
456 {
457 Elf32_Addr *const reloc_addr = reloc_addr_arg;
458 *reloc_addr = l_addr + reloc->r_addend;
459 }
460 # endif /* !RTLD_BOOTSTRAP */
461
462 static inline void
463 __attribute__ ((always_inline))
464 elf_machine_lazy_rel (struct link_map *map, struct r_scope_elem *scope[],
465 Elf32_Addr l_addr, const Elf32_Rel *reloc,
466 int skip_ifunc)
467 {
468 Elf32_Addr *const reloc_addr = (void *) (l_addr + reloc->r_offset);
469 const unsigned int r_type = ELF32_R_TYPE (reloc->r_info);
470 /* Check for unexpected PLT reloc type. */
471 if (__glibc_likely (r_type == R_386_JMP_SLOT))
472 {
473 /* Prelink has been deprecated. */
474 if (__glibc_likely (map->l_mach.plt == 0))
475 *reloc_addr += l_addr;
476 else
477 *reloc_addr = (map->l_mach.plt
478 + (((Elf32_Addr) reloc_addr) - map->l_mach.gotplt) * 4);
479 }
480 else if (__glibc_likely (r_type == R_386_TLS_DESC))
481 {
482 const Elf32_Rel *const r = reloc;
483 /* The code below was borrowed from elf_dynamic_do_rel(). */
484 const ElfW(Sym) *const symtab =
485 (const void *) D_PTR (map, l_info[DT_SYMTAB]);
486
487 /* Always initialize TLS descriptors completely at load time, in
488 case static TLS is allocated for it that requires locking. */
489 # ifdef RTLD_BOOTSTRAP
490 /* The dynamic linker always uses versioning. */
491 assert (map->l_info[VERSYMIDX (DT_VERSYM)] != NULL);
492 # else
493 if (map->l_info[VERSYMIDX (DT_VERSYM)])
494 # endif
495 {
496 const ElfW(Half) *const version =
497 (const void *) D_PTR (map, l_info[VERSYMIDX (DT_VERSYM)]);
498 ElfW(Half) ndx = version[ELFW(R_SYM) (r->r_info)] & 0x7fff;
499 elf_machine_rel (map, scope, r, &symtab[ELFW(R_SYM) (r->r_info)],
500 &map->l_versions[ndx],
501 (void *) (l_addr + r->r_offset), skip_ifunc);
502 }
503 # ifndef RTLD_BOOTSTRAP
504 else
505 elf_machine_rel (map, scope, r, &symtab[ELFW(R_SYM) (r->r_info)], NULL,
506 (void *) (l_addr + r->r_offset), skip_ifunc);
507 # endif
508 }
509 else if (__glibc_unlikely (r_type == R_386_IRELATIVE))
510 {
511 Elf32_Addr value = map->l_addr + *reloc_addr;
512 if (__glibc_likely (!skip_ifunc))
513 value = ((Elf32_Addr (*) (void)) value) ();
514 *reloc_addr = value;
515 }
516 else
517 _dl_reloc_bad_type (map, r_type, 1);
518 }
519
520 #endif /* RESOLVE_MAP */