1 /* Handle SVR4 shared libraries for GDB, the GNU Debugger.
3 Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1998, 1999, 2000,
4 2001, 2003, 2004, 2005, 2006, 2007 Free Software Foundation, Inc.
6 This file is part of GDB.
8 This program is free software; you can redistribute it and/or modify
9 it under the terms of the GNU General Public License as published by
10 the Free Software Foundation; either version 2 of the License, or
11 (at your option) any later version.
13 This program is distributed in the hope that it will be useful,
14 but WITHOUT ANY WARRANTY; without even the implied warranty of
15 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
16 GNU General Public License for more details.
18 You should have received a copy of the GNU General Public License
19 along with this program; if not, write to the Free Software
20 Foundation, Inc., 51 Franklin Street, Fifth Floor,
21 Boston, MA 02110-1301, USA. */
25 #include "elf/external.h"
26 #include "elf/common.h"
37 #include "gdb_assert.h"
41 #include "solib-svr4.h"
43 #include "bfd-target.h"
47 static struct link_map_offsets *svr4_fetch_link_map_offsets (void);
48 static int svr4_have_link_map_offsets (void);
50 /* This hook is set to a function that provides native link map
51 offsets if the code in solib-legacy.c is linked in. */
52 struct link_map_offsets *(*legacy_svr4_fetch_link_map_offsets_hook) (void);
54 /* Link map info to include in an allocated so_list entry */
58 /* Pointer to copy of link map from inferior. The type is char *
59 rather than void *, so that we may use byte offsets to find the
60 various fields without the need for a cast. */
63 /* Amount by which addresses in the binary should be relocated to
64 match the inferior. This could most often be taken directly
65 from lm, but when prelinking is involved and the prelink base
66 address changes, we may need a different offset, we want to
67 warn about the difference and compute it only once. */
71 /* On SVR4 systems, a list of symbols in the dynamic linker where
72 GDB can try to place a breakpoint to monitor shared library
75 If none of these symbols are found, or other errors occur, then
76 SVR4 systems will fall back to using a symbol as the "startup
77 mapping complete" breakpoint address. */
79 static char *solib_break_names[] =
90 #define BKPT_AT_SYMBOL 1
92 #if defined (BKPT_AT_SYMBOL)
93 static char *bkpt_names[] =
95 #ifdef SOLIB_BKPT_NAME
96 SOLIB_BKPT_NAME, /* Prefer configured name if it exists. */
105 static char *main_name_list[] =
111 /* link map access functions */
114 LM_ADDR_FROM_LINK_MAP (struct so_list *so)
116 struct link_map_offsets *lmo = svr4_fetch_link_map_offsets ();
118 return extract_typed_address (so->lm_info->lm + lmo->l_addr_offset,
119 builtin_type_void_data_ptr);
123 HAS_LM_DYNAMIC_FROM_LINK_MAP ()
125 struct link_map_offsets *lmo = svr4_fetch_link_map_offsets ();
127 return lmo->l_ld_offset >= 0;
131 LM_DYNAMIC_FROM_LINK_MAP (struct so_list *so)
133 struct link_map_offsets *lmo = svr4_fetch_link_map_offsets ();
135 return extract_typed_address (so->lm_info->lm + lmo->l_ld_offset,
136 builtin_type_void_data_ptr);
140 LM_ADDR_CHECK (struct so_list *so, bfd *abfd)
142 if (so->lm_info->l_addr == (CORE_ADDR)-1)
144 struct bfd_section *dyninfo_sect;
145 CORE_ADDR l_addr, l_dynaddr, dynaddr, align = 0x1000;
147 l_addr = LM_ADDR_FROM_LINK_MAP (so);
149 if (! abfd || ! HAS_LM_DYNAMIC_FROM_LINK_MAP ())
152 l_dynaddr = LM_DYNAMIC_FROM_LINK_MAP (so);
154 dyninfo_sect = bfd_get_section_by_name (abfd, ".dynamic");
155 if (dyninfo_sect == NULL)
158 dynaddr = bfd_section_vma (abfd, dyninfo_sect);
160 if (dynaddr + l_addr != l_dynaddr)
162 if (bfd_get_flavour (abfd) == bfd_target_elf_flavour)
164 Elf_Internal_Ehdr *ehdr = elf_tdata (abfd)->elf_header;
165 Elf_Internal_Phdr *phdr = elf_tdata (abfd)->phdr;
170 for (i = 0; i < ehdr->e_phnum; i++)
171 if (phdr[i].p_type == PT_LOAD && phdr[i].p_align > align)
172 align = phdr[i].p_align;
175 /* Turn it into a mask. */
178 /* If the changes match the alignment requirements, we
179 assume we're using a core file that was generated by the
180 same binary, just prelinked with a different base offset.
181 If it doesn't match, we may have a different binary, the
182 same binary with the dynamic table loaded at an unrelated
183 location, or anything, really. To avoid regressions,
184 don't adjust the base offset in the latter case, although
185 odds are that, if things really changed, debugging won't
187 if ((l_addr & align) == ((l_dynaddr - dynaddr) & align))
189 l_addr = l_dynaddr - dynaddr;
191 warning (_(".dynamic section for \"%s\" "
192 "is not at the expected address"), so->so_name);
193 warning (_("difference appears to be caused by prelink, "
194 "adjusting expectations"));
197 warning (_(".dynamic section for \"%s\" "
198 "is not at the expected address "
199 "(wrong library or version mismatch?)"), so->so_name);
203 so->lm_info->l_addr = l_addr;
206 return so->lm_info->l_addr;
210 LM_NEXT (struct so_list *so)
212 struct link_map_offsets *lmo = svr4_fetch_link_map_offsets ();
214 return extract_typed_address (so->lm_info->lm + lmo->l_next_offset,
215 builtin_type_void_data_ptr);
219 LM_NAME (struct so_list *so)
221 struct link_map_offsets *lmo = svr4_fetch_link_map_offsets ();
223 return extract_typed_address (so->lm_info->lm + lmo->l_name_offset,
224 builtin_type_void_data_ptr);
228 IGNORE_FIRST_LINK_MAP_ENTRY (struct so_list *so)
230 struct link_map_offsets *lmo = svr4_fetch_link_map_offsets ();
232 /* Assume that everything is a library if the dynamic loader was loaded
233 late by a static executable. */
234 if (bfd_get_section_by_name (exec_bfd, ".dynamic") == NULL)
237 return extract_typed_address (so->lm_info->lm + lmo->l_prev_offset,
238 builtin_type_void_data_ptr) == 0;
241 static CORE_ADDR debug_base; /* Base of dynamic linker structures */
243 /* Validity flag for debug_loader_offset. */
244 static int debug_loader_offset_p;
246 /* Load address for the dynamic linker, inferred. */
247 static CORE_ADDR debug_loader_offset;
249 /* Name of the dynamic linker, valid if debug_loader_offset_p. */
250 static char *debug_loader_name;
252 /* Local function prototypes */
254 static int match_main (char *);
256 static CORE_ADDR bfd_lookup_symbol (bfd *, char *);
262 bfd_lookup_symbol -- lookup the value for a specific symbol
266 CORE_ADDR bfd_lookup_symbol (bfd *abfd, char *symname)
270 An expensive way to lookup the value of a single symbol for
271 bfd's that are only temporary anyway. This is used by the
272 shared library support to find the address of the debugger
273 notification routine in the shared library.
275 The returned symbol may be in a code or data section; functions
276 will normally be in a code section, but may be in a data section
277 if this architecture uses function descriptors.
279 Note that 0 is specifically allowed as an error return (no
284 bfd_lookup_symbol (bfd *abfd, char *symname)
288 asymbol **symbol_table;
289 unsigned int number_of_symbols;
291 struct cleanup *back_to;
292 CORE_ADDR symaddr = 0;
294 storage_needed = bfd_get_symtab_upper_bound (abfd);
296 if (storage_needed > 0)
298 symbol_table = (asymbol **) xmalloc (storage_needed);
299 back_to = make_cleanup (xfree, symbol_table);
300 number_of_symbols = bfd_canonicalize_symtab (abfd, symbol_table);
302 for (i = 0; i < number_of_symbols; i++)
304 sym = *symbol_table++;
305 if (strcmp (sym->name, symname) == 0
306 && (sym->section->flags & (SEC_CODE | SEC_DATA)) != 0)
308 /* BFD symbols are section relative. */
309 symaddr = sym->value + sym->section->vma;
313 do_cleanups (back_to);
319 /* On FreeBSD, the dynamic linker is stripped by default. So we'll
320 have to check the dynamic string table too. */
322 storage_needed = bfd_get_dynamic_symtab_upper_bound (abfd);
324 if (storage_needed > 0)
326 symbol_table = (asymbol **) xmalloc (storage_needed);
327 back_to = make_cleanup (xfree, symbol_table);
328 number_of_symbols = bfd_canonicalize_dynamic_symtab (abfd, symbol_table);
330 for (i = 0; i < number_of_symbols; i++)
332 sym = *symbol_table++;
334 if (strcmp (sym->name, symname) == 0
335 && (sym->section->flags & (SEC_CODE | SEC_DATA)) != 0)
337 /* BFD symbols are section relative. */
338 symaddr = sym->value + sym->section->vma;
342 do_cleanups (back_to);
348 /* Scan for DYNTAG in .dynamic section of ABFD. If DYNTAG is found 1 is
349 returned and the corresponding PTR is set. */
352 scan_dyntag (int dyntag, bfd *abfd, CORE_ADDR *ptr)
354 int arch_size, step, sect_size;
356 CORE_ADDR dyn_ptr, dyn_addr;
357 gdb_byte *bufend, *buf;
358 Elf32_External_Dyn *x_dynp_32;
359 Elf64_External_Dyn *x_dynp_64;
360 struct bfd_section *sect;
364 arch_size = bfd_get_arch_size (abfd);
368 /* Find the start address of the .dynamic section. */
369 sect = bfd_get_section_by_name (abfd, ".dynamic");
372 dyn_addr = bfd_section_vma (abfd, sect);
374 /* Read in .dynamic section, silently ignore errors. */
375 sect_size = bfd_section_size (abfd, sect);
376 buf = alloca (sect_size);
377 if (target_read_memory (dyn_addr, buf, sect_size))
379 /* If target_read_memory fails, try reading the BFD file. */
380 if (!bfd_get_section_contents (abfd, sect,
385 /* Iterate over BUF and scan for DYNTAG. If found, set PTR and return. */
386 step = (arch_size == 32) ? sizeof (Elf32_External_Dyn)
387 : sizeof (Elf64_External_Dyn);
388 for (bufend = buf + sect_size;
394 x_dynp_32 = (Elf32_External_Dyn *) buf;
395 dyn_tag = bfd_h_get_32 (abfd, (bfd_byte *) x_dynp_32->d_tag);
396 dyn_ptr = bfd_h_get_32 (abfd, (bfd_byte *) x_dynp_32->d_un.d_ptr);
400 x_dynp_64 = (Elf64_External_Dyn *) buf;
401 dyn_tag = bfd_h_get_64 (abfd, (bfd_byte *) x_dynp_64->d_tag);
402 dyn_ptr = bfd_h_get_64 (abfd, (bfd_byte *) x_dynp_64->d_un.d_ptr);
404 if (dyn_tag == DT_NULL)
406 if (dyn_tag == dyntag)
422 elf_locate_base -- locate the base address of dynamic linker structs
423 for SVR4 elf targets.
427 CORE_ADDR elf_locate_base (void)
431 For SVR4 elf targets the address of the dynamic linker's runtime
432 structure is contained within the dynamic info section in the
433 executable file. The dynamic section is also mapped into the
434 inferior address space. Because the runtime loader fills in the
435 real address before starting the inferior, we have to read in the
436 dynamic info section from the inferior address space.
437 If there are any errors while trying to find the address, we
438 silently return 0, otherwise the found address is returned.
443 elf_locate_base (void)
445 struct minimal_symbol *msymbol;
449 if (scan_dyntag (DT_DEBUG, exec_bfd, &dyn_ptr))
452 /* Find DT_MIPS_RLD_MAP. */
453 if (scan_dyntag (DT_MIPS_RLD_MAP, exec_bfd, &dyn_ptr))
456 int pbuf_size = TYPE_LENGTH (builtin_type_void_data_ptr);
457 pbuf = alloca (pbuf_size);
458 /* DT_MIPS_RLD_MAP contains a pointer to the address
459 of the dynamic link structure. */
460 if (target_read_memory (dyn_ptr, pbuf, pbuf_size))
462 return extract_typed_address (pbuf, builtin_type_void_data_ptr);
465 /* This may be a static executable. Look for the symbol
466 conventionally named _r_debug, as a last resort. */
467 msymbol = lookup_minimal_symbol ("_r_debug", NULL, symfile_objfile);
469 return SYMBOL_VALUE_ADDRESS (msymbol);
471 /* DT_DEBUG entry not found. */
479 locate_base -- locate the base address of dynamic linker structs
483 CORE_ADDR locate_base (void)
487 For both the SunOS and SVR4 shared library implementations, if the
488 inferior executable has been linked dynamically, there is a single
489 address somewhere in the inferior's data space which is the key to
490 locating all of the dynamic linker's runtime structures. This
491 address is the value of the debug base symbol. The job of this
492 function is to find and return that address, or to return 0 if there
493 is no such address (the executable is statically linked for example).
495 For SunOS, the job is almost trivial, since the dynamic linker and
496 all of it's structures are statically linked to the executable at
497 link time. Thus the symbol for the address we are looking for has
498 already been added to the minimal symbol table for the executable's
499 objfile at the time the symbol file's symbols were read, and all we
500 have to do is look it up there. Note that we explicitly do NOT want
501 to find the copies in the shared library.
503 The SVR4 version is a bit more complicated because the address
504 is contained somewhere in the dynamic info section. We have to go
505 to a lot more work to discover the address of the debug base symbol.
506 Because of this complexity, we cache the value we find and return that
507 value on subsequent invocations. Note there is no copy in the
508 executable symbol tables.
515 /* Check to see if we have a currently valid address, and if so, avoid
516 doing all this work again and just return the cached address. If
517 we have no cached address, try to locate it in the dynamic info
518 section for ELF executables. There's no point in doing any of this
519 though if we don't have some link map offsets to work with. */
521 if (debug_base == 0 && svr4_have_link_map_offsets ())
524 && bfd_get_flavour (exec_bfd) == bfd_target_elf_flavour)
525 debug_base = elf_locate_base ();
530 /* Find the first element in the inferior's dynamic link map, and
531 return its address in the inferior.
533 FIXME: Perhaps we should validate the info somehow, perhaps by
534 checking r_version for a known version number, or r_state for
538 solib_svr4_r_map (void)
540 struct link_map_offsets *lmo = svr4_fetch_link_map_offsets ();
542 return read_memory_typed_address (debug_base + lmo->r_map_offset,
543 builtin_type_void_data_ptr);
546 /* Find the link map for the dynamic linker (if it is not in the
547 normal list of loaded shared objects). */
550 solib_svr4_r_ldsomap (void)
552 struct link_map_offsets *lmo = svr4_fetch_link_map_offsets ();
555 /* Check version, and return zero if `struct r_debug' doesn't have
556 the r_ldsomap member. */
557 version = read_memory_unsigned_integer (debug_base + lmo->r_version_offset,
558 lmo->r_version_size);
559 if (version < 2 || lmo->r_ldsomap_offset == -1)
562 return read_memory_typed_address (debug_base + lmo->r_ldsomap_offset,
563 builtin_type_void_data_ptr);
570 open_symbol_file_object
574 void open_symbol_file_object (void *from_tty)
578 If no open symbol file, attempt to locate and open the main symbol
579 file. On SVR4 systems, this is the first link map entry. If its
580 name is here, we can open it. Useful when attaching to a process
581 without first loading its symbol file.
583 If FROM_TTYP dereferences to a non-zero integer, allow messages to
584 be printed. This parameter is a pointer rather than an int because
585 open_symbol_file_object() is called via catch_errors() and
586 catch_errors() requires a pointer argument. */
589 open_symbol_file_object (void *from_ttyp)
591 CORE_ADDR lm, l_name;
594 int from_tty = *(int *)from_ttyp;
595 struct link_map_offsets *lmo = svr4_fetch_link_map_offsets ();
596 int l_name_size = TYPE_LENGTH (builtin_type_void_data_ptr);
597 gdb_byte *l_name_buf = xmalloc (l_name_size);
598 struct cleanup *cleanups = make_cleanup (xfree, l_name_buf);
601 if (!query ("Attempt to reload symbols from process? "))
604 if ((debug_base = locate_base ()) == 0)
605 return 0; /* failed somehow... */
607 /* First link map member should be the executable. */
608 lm = solib_svr4_r_map ();
610 return 0; /* failed somehow... */
612 /* Read address of name from target memory to GDB. */
613 read_memory (lm + lmo->l_name_offset, l_name_buf, l_name_size);
615 /* Convert the address to host format. */
616 l_name = extract_typed_address (l_name_buf, builtin_type_void_data_ptr);
618 /* Free l_name_buf. */
619 do_cleanups (cleanups);
622 return 0; /* No filename. */
624 /* Now fetch the filename from target memory. */
625 target_read_string (l_name, &filename, SO_NAME_MAX_PATH_SIZE - 1, &errcode);
629 warning (_("failed to read exec filename from attached file: %s"),
630 safe_strerror (errcode));
634 make_cleanup (xfree, filename);
635 /* Have a pathname: read the symbol file. */
636 symbol_file_add_main (filename, from_tty);
641 /* If no shared library information is available from the dynamic
642 linker, build a fallback list from other sources. */
644 static struct so_list *
645 svr4_default_sos (void)
647 struct so_list *head = NULL;
648 struct so_list **link_ptr = &head;
650 if (debug_loader_offset_p)
652 struct so_list *new = XZALLOC (struct so_list);
654 new->lm_info = xmalloc (sizeof (struct lm_info));
656 /* Nothing will ever check the cached copy of the link
657 map if we set l_addr. */
658 new->lm_info->l_addr = debug_loader_offset;
659 new->lm_info->lm = NULL;
661 strncpy (new->so_name, debug_loader_name, SO_NAME_MAX_PATH_SIZE - 1);
662 new->so_name[SO_NAME_MAX_PATH_SIZE - 1] = '\0';
663 strcpy (new->so_original_name, new->so_name);
666 link_ptr = &new->next;
674 current_sos -- build a list of currently loaded shared objects
678 struct so_list *current_sos ()
682 Build a list of `struct so_list' objects describing the shared
683 objects currently loaded in the inferior. This list does not
684 include an entry for the main executable file.
686 Note that we only gather information directly available from the
687 inferior --- we don't examine any of the shared library files
688 themselves. The declaration of `struct so_list' says which fields
689 we provide values for. */
691 static struct so_list *
692 svr4_current_sos (void)
695 struct so_list *head = 0;
696 struct so_list **link_ptr = &head;
697 CORE_ADDR ldsomap = 0;
699 /* Make sure we've looked up the inferior's dynamic linker's base
703 debug_base = locate_base ();
705 /* If we can't find the dynamic linker's base structure, this
706 must not be a dynamically linked executable. Hmm. */
708 return svr4_default_sos ();
711 /* Walk the inferior's link map list, and build our list of
712 `struct so_list' nodes. */
713 lm = solib_svr4_r_map ();
717 struct link_map_offsets *lmo = svr4_fetch_link_map_offsets ();
718 struct so_list *new = XZALLOC (struct so_list);
719 struct cleanup *old_chain = make_cleanup (xfree, new);
721 new->lm_info = xmalloc (sizeof (struct lm_info));
722 make_cleanup (xfree, new->lm_info);
724 new->lm_info->l_addr = (CORE_ADDR)-1;
725 new->lm_info->lm = xzalloc (lmo->link_map_size);
726 make_cleanup (xfree, new->lm_info->lm);
728 read_memory (lm, new->lm_info->lm, lmo->link_map_size);
732 /* For SVR4 versions, the first entry in the link map is for the
733 inferior executable, so we must ignore it. For some versions of
734 SVR4, it has no name. For others (Solaris 2.3 for example), it
735 does have a name, so we can no longer use a missing name to
736 decide when to ignore it. */
737 if (IGNORE_FIRST_LINK_MAP_ENTRY (new) && ldsomap == 0)
744 /* Extract this shared object's name. */
745 target_read_string (LM_NAME (new), &buffer,
746 SO_NAME_MAX_PATH_SIZE - 1, &errcode);
748 warning (_("Can't read pathname for load map: %s."),
749 safe_strerror (errcode));
752 strncpy (new->so_name, buffer, SO_NAME_MAX_PATH_SIZE - 1);
753 new->so_name[SO_NAME_MAX_PATH_SIZE - 1] = '\0';
755 strcpy (new->so_original_name, new->so_name);
758 /* If this entry has no name, or its name matches the name
759 for the main executable, don't include it in the list. */
760 if (! new->so_name[0]
761 || match_main (new->so_name))
767 link_ptr = &new->next;
771 /* On Solaris, the dynamic linker is not in the normal list of
772 shared objects, so make sure we pick it up too. Having
773 symbol information for the dynamic linker is quite crucial
774 for skipping dynamic linker resolver code. */
775 if (lm == 0 && ldsomap == 0)
776 lm = ldsomap = solib_svr4_r_ldsomap ();
778 discard_cleanups (old_chain);
782 return svr4_default_sos ();
787 /* Get the address of the link_map for a given OBJFILE. Loop through
788 the link maps, and return the address of the one corresponding to
789 the given objfile. Note that this function takes into account that
790 objfile can be the main executable, not just a shared library. The
791 main executable has always an empty name field in the linkmap. */
794 svr4_fetch_objfile_link_map (struct objfile *objfile)
798 if ((debug_base = locate_base ()) == 0)
799 return 0; /* failed somehow... */
801 /* Position ourselves on the first link map. */
802 lm = solib_svr4_r_map ();
805 /* Get info on the layout of the r_debug and link_map structures. */
806 struct link_map_offsets *lmo = svr4_fetch_link_map_offsets ();
809 struct lm_info objfile_lm_info;
810 struct cleanup *old_chain;
811 CORE_ADDR name_address;
812 int l_name_size = TYPE_LENGTH (builtin_type_void_data_ptr);
813 gdb_byte *l_name_buf = xmalloc (l_name_size);
814 old_chain = make_cleanup (xfree, l_name_buf);
816 /* Set up the buffer to contain the portion of the link_map
817 structure that gdb cares about. Note that this is not the
818 whole link_map structure. */
819 objfile_lm_info.lm = xzalloc (lmo->link_map_size);
820 make_cleanup (xfree, objfile_lm_info.lm);
822 /* Read the link map into our internal structure. */
823 read_memory (lm, objfile_lm_info.lm, lmo->link_map_size);
825 /* Read address of name from target memory to GDB. */
826 read_memory (lm + lmo->l_name_offset, l_name_buf, l_name_size);
828 /* Extract this object's name. */
829 name_address = extract_typed_address (l_name_buf,
830 builtin_type_void_data_ptr);
831 target_read_string (name_address, &buffer,
832 SO_NAME_MAX_PATH_SIZE - 1, &errcode);
833 make_cleanup (xfree, buffer);
835 warning (_("Can't read pathname for load map: %s."),
836 safe_strerror (errcode));
839 /* Is this the linkmap for the file we want? */
840 /* If the file is not a shared library and has no name,
841 we are sure it is the main executable, so we return that. */
844 && ((strcmp (buffer, objfile->name) == 0)
845 || (!(objfile->flags & OBJF_SHARED)
846 && (strcmp (buffer, "") == 0))))
848 do_cleanups (old_chain);
852 /* Not the file we wanted, continue checking. */
853 lm = extract_typed_address (objfile_lm_info.lm + lmo->l_next_offset,
854 builtin_type_void_data_ptr);
855 do_cleanups (old_chain);
860 /* On some systems, the only way to recognize the link map entry for
861 the main executable file is by looking at its name. Return
862 non-zero iff SONAME matches one of the known main executable names. */
865 match_main (char *soname)
869 for (mainp = main_name_list; *mainp != NULL; mainp++)
871 if (strcmp (soname, *mainp) == 0)
878 /* Return 1 if PC lies in the dynamic symbol resolution code of the
879 SVR4 run time loader. */
880 static CORE_ADDR interp_text_sect_low;
881 static CORE_ADDR interp_text_sect_high;
882 static CORE_ADDR interp_plt_sect_low;
883 static CORE_ADDR interp_plt_sect_high;
886 svr4_in_dynsym_resolve_code (CORE_ADDR pc)
888 return ((pc >= interp_text_sect_low && pc < interp_text_sect_high)
889 || (pc >= interp_plt_sect_low && pc < interp_plt_sect_high)
890 || in_plt_section (pc, NULL));
893 /* Given an executable's ABFD and target, compute the entry-point
897 exec_entry_point (struct bfd *abfd, struct target_ops *targ)
899 /* KevinB wrote ... for most targets, the address returned by
900 bfd_get_start_address() is the entry point for the start
901 function. But, for some targets, bfd_get_start_address() returns
902 the address of a function descriptor from which the entry point
903 address may be extracted. This address is extracted by
904 gdbarch_convert_from_func_ptr_addr(). The method
905 gdbarch_convert_from_func_ptr_addr() is the merely the identify
906 function for targets which don't use function descriptors. */
907 return gdbarch_convert_from_func_ptr_addr (current_gdbarch,
908 bfd_get_start_address (abfd),
916 enable_break -- arrange for dynamic linker to hit breakpoint
920 int enable_break (void)
924 Both the SunOS and the SVR4 dynamic linkers have, as part of their
925 debugger interface, support for arranging for the inferior to hit
926 a breakpoint after mapping in the shared libraries. This function
927 enables that breakpoint.
929 For SunOS, there is a special flag location (in_debugger) which we
930 set to 1. When the dynamic linker sees this flag set, it will set
931 a breakpoint at a location known only to itself, after saving the
932 original contents of that place and the breakpoint address itself,
933 in it's own internal structures. When we resume the inferior, it
934 will eventually take a SIGTRAP when it runs into the breakpoint.
935 We handle this (in a different place) by restoring the contents of
936 the breakpointed location (which is only known after it stops),
937 chasing around to locate the shared libraries that have been
938 loaded, then resuming.
940 For SVR4, the debugger interface structure contains a member (r_brk)
941 which is statically initialized at the time the shared library is
942 built, to the offset of a function (_r_debug_state) which is guaran-
943 teed to be called once before mapping in a library, and again when
944 the mapping is complete. At the time we are examining this member,
945 it contains only the unrelocated offset of the function, so we have
946 to do our own relocation. Later, when the dynamic linker actually
947 runs, it relocates r_brk to be the actual address of _r_debug_state().
949 The debugger interface structure also contains an enumeration which
950 is set to either RT_ADD or RT_DELETE prior to changing the mapping,
951 depending upon whether or not the library is being mapped or unmapped,
952 and then set to RT_CONSISTENT after the library is mapped/unmapped.
958 #ifdef BKPT_AT_SYMBOL
960 struct minimal_symbol *msymbol;
962 asection *interp_sect;
964 /* First, remove all the solib event breakpoints. Their addresses
965 may have changed since the last time we ran the program. */
966 remove_solib_event_breakpoints ();
968 interp_text_sect_low = interp_text_sect_high = 0;
969 interp_plt_sect_low = interp_plt_sect_high = 0;
971 /* Find the .interp section; if not found, warn the user and drop
972 into the old breakpoint at symbol code. */
973 interp_sect = bfd_get_section_by_name (exec_bfd, ".interp");
976 unsigned int interp_sect_size;
978 CORE_ADDR load_addr = 0;
979 int load_addr_found = 0;
982 struct target_ops *tmp_bfd_target;
984 char *tmp_pathname = NULL;
985 CORE_ADDR sym_addr = 0;
987 /* Read the contents of the .interp section into a local buffer;
988 the contents specify the dynamic linker this program uses. */
989 interp_sect_size = bfd_section_size (exec_bfd, interp_sect);
990 buf = alloca (interp_sect_size);
991 bfd_get_section_contents (exec_bfd, interp_sect,
992 buf, 0, interp_sect_size);
994 /* Now we need to figure out where the dynamic linker was
995 loaded so that we can load its symbols and place a breakpoint
996 in the dynamic linker itself.
998 This address is stored on the stack. However, I've been unable
999 to find any magic formula to find it for Solaris (appears to
1000 be trivial on GNU/Linux). Therefore, we have to try an alternate
1001 mechanism to find the dynamic linker's base address. */
1003 /* TODO drow/2006-09-12: This is somewhat fragile, because it
1004 relies on read_pc. On both Solaris and GNU/Linux we can use
1005 the AT_BASE auxilliary entry, which GDB now knows how to
1006 access, to find the base address. */
1008 tmp_fd = solib_open (buf, &tmp_pathname);
1010 tmp_bfd = bfd_fopen (tmp_pathname, gnutarget, FOPEN_RB, tmp_fd);
1012 if (tmp_bfd == NULL)
1013 goto bkpt_at_symbol;
1015 /* Make sure the dynamic linker's really a useful object. */
1016 if (!bfd_check_format (tmp_bfd, bfd_object))
1018 warning (_("Unable to grok dynamic linker %s as an object file"), buf);
1019 bfd_close (tmp_bfd);
1020 goto bkpt_at_symbol;
1023 /* Now convert the TMP_BFD into a target. That way target, as
1024 well as BFD operations can be used. Note that closing the
1025 target will also close the underlying bfd. */
1026 tmp_bfd_target = target_bfd_reopen (tmp_bfd);
1028 /* On a running target, we can get the dynamic linker's base
1029 address from the shared library table. */
1030 solib_add (NULL, 0, ¤t_target, auto_solib_add);
1031 so = master_so_list ();
1034 if (strcmp (buf, so->so_original_name) == 0)
1036 load_addr_found = 1;
1037 load_addr = LM_ADDR_CHECK (so, tmp_bfd);
1043 /* Otherwise we find the dynamic linker's base address by examining
1044 the current pc (which should point at the entry point for the
1045 dynamic linker) and subtracting the offset of the entry point. */
1046 if (!load_addr_found)
1048 load_addr = (read_pc ()
1049 - exec_entry_point (tmp_bfd, tmp_bfd_target));
1050 debug_loader_name = xstrdup (buf);
1051 debug_loader_offset_p = 1;
1052 debug_loader_offset = load_addr;
1053 solib_add (NULL, 0, ¤t_target, auto_solib_add);
1056 /* Record the relocated start and end address of the dynamic linker
1057 text and plt section for svr4_in_dynsym_resolve_code. */
1058 interp_sect = bfd_get_section_by_name (tmp_bfd, ".text");
1061 interp_text_sect_low =
1062 bfd_section_vma (tmp_bfd, interp_sect) + load_addr;
1063 interp_text_sect_high =
1064 interp_text_sect_low + bfd_section_size (tmp_bfd, interp_sect);
1066 interp_sect = bfd_get_section_by_name (tmp_bfd, ".plt");
1069 interp_plt_sect_low =
1070 bfd_section_vma (tmp_bfd, interp_sect) + load_addr;
1071 interp_plt_sect_high =
1072 interp_plt_sect_low + bfd_section_size (tmp_bfd, interp_sect);
1075 /* Now try to set a breakpoint in the dynamic linker. */
1076 for (bkpt_namep = solib_break_names; *bkpt_namep != NULL; bkpt_namep++)
1078 sym_addr = bfd_lookup_symbol (tmp_bfd, *bkpt_namep);
1084 /* Convert 'sym_addr' from a function pointer to an address.
1085 Because we pass tmp_bfd_target instead of the current
1086 target, this will always produce an unrelocated value. */
1087 sym_addr = gdbarch_convert_from_func_ptr_addr (current_gdbarch,
1091 /* We're done with both the temporary bfd and target. Remember,
1092 closing the target closes the underlying bfd. */
1093 target_close (tmp_bfd_target, 0);
1097 create_solib_event_breakpoint (load_addr + sym_addr);
1101 /* For whatever reason we couldn't set a breakpoint in the dynamic
1102 linker. Warn and drop into the old code. */
1104 warning (_("Unable to find dynamic linker breakpoint function.\n"
1105 "GDB will be unable to debug shared library initializers\n"
1106 "and track explicitly loaded dynamic code."));
1109 /* Scan through the lists of symbols, trying to look up the symbol and
1110 set a breakpoint there. Terminate loop when we/if we succeed. */
1112 for (bkpt_namep = solib_break_names; *bkpt_namep != NULL; bkpt_namep++)
1114 msymbol = lookup_minimal_symbol (*bkpt_namep, NULL, symfile_objfile);
1115 if ((msymbol != NULL) && (SYMBOL_VALUE_ADDRESS (msymbol) != 0))
1117 create_solib_event_breakpoint (SYMBOL_VALUE_ADDRESS (msymbol));
1122 for (bkpt_namep = bkpt_names; *bkpt_namep != NULL; bkpt_namep++)
1124 msymbol = lookup_minimal_symbol (*bkpt_namep, NULL, symfile_objfile);
1125 if ((msymbol != NULL) && (SYMBOL_VALUE_ADDRESS (msymbol) != 0))
1127 create_solib_event_breakpoint (SYMBOL_VALUE_ADDRESS (msymbol));
1131 #endif /* BKPT_AT_SYMBOL */
1140 special_symbol_handling -- additional shared library symbol handling
1144 void special_symbol_handling ()
1148 Once the symbols from a shared object have been loaded in the usual
1149 way, we are called to do any system specific symbol handling that
1152 For SunOS4, this consisted of grunging around in the dynamic
1153 linkers structures to find symbol definitions for "common" symbols
1154 and adding them to the minimal symbol table for the runtime common
1157 However, for SVR4, there's nothing to do.
1162 svr4_special_symbol_handling (void)
1166 /* Relocate the main executable. This function should be called upon
1167 stopping the inferior process at the entry point to the program.
1168 The entry point from BFD is compared to the PC and if they are
1169 different, the main executable is relocated by the proper amount.
1171 As written it will only attempt to relocate executables which
1172 lack interpreter sections. It seems likely that only dynamic
1173 linker executables will get relocated, though it should work
1174 properly for a position-independent static executable as well. */
1177 svr4_relocate_main_executable (void)
1179 asection *interp_sect;
1180 CORE_ADDR pc = read_pc ();
1182 /* Decide if the objfile needs to be relocated. As indicated above,
1183 we will only be here when execution is stopped at the beginning
1184 of the program. Relocation is necessary if the address at which
1185 we are presently stopped differs from the start address stored in
1186 the executable AND there's no interpreter section. The condition
1187 regarding the interpreter section is very important because if
1188 there *is* an interpreter section, execution will begin there
1189 instead. When there is an interpreter section, the start address
1190 is (presumably) used by the interpreter at some point to start
1191 execution of the program.
1193 If there is an interpreter, it is normal for it to be set to an
1194 arbitrary address at the outset. The job of finding it is
1195 handled in enable_break().
1197 So, to summarize, relocations are necessary when there is no
1198 interpreter section and the start address obtained from the
1199 executable is different from the address at which GDB is
1202 [ The astute reader will note that we also test to make sure that
1203 the executable in question has the DYNAMIC flag set. It is my
1204 opinion that this test is unnecessary (undesirable even). It
1205 was added to avoid inadvertent relocation of an executable
1206 whose e_type member in the ELF header is not ET_DYN. There may
1207 be a time in the future when it is desirable to do relocations
1208 on other types of files as well in which case this condition
1209 should either be removed or modified to accomodate the new file
1210 type. (E.g, an ET_EXEC executable which has been built to be
1211 position-independent could safely be relocated by the OS if
1212 desired. It is true that this violates the ABI, but the ABI
1213 has been known to be bent from time to time.) - Kevin, Nov 2000. ]
1216 interp_sect = bfd_get_section_by_name (exec_bfd, ".interp");
1217 if (interp_sect == NULL
1218 && (bfd_get_file_flags (exec_bfd) & DYNAMIC) != 0
1219 && (exec_entry_point (exec_bfd, &exec_ops) != pc))
1221 struct cleanup *old_chain;
1222 struct section_offsets *new_offsets;
1224 CORE_ADDR displacement;
1226 /* It is necessary to relocate the objfile. The amount to
1227 relocate by is simply the address at which we are stopped
1228 minus the starting address from the executable.
1230 We relocate all of the sections by the same amount. This
1231 behavior is mandated by recent editions of the System V ABI.
1232 According to the System V Application Binary Interface,
1233 Edition 4.1, page 5-5:
1235 ... Though the system chooses virtual addresses for
1236 individual processes, it maintains the segments' relative
1237 positions. Because position-independent code uses relative
1238 addressesing between segments, the difference between
1239 virtual addresses in memory must match the difference
1240 between virtual addresses in the file. The difference
1241 between the virtual address of any segment in memory and
1242 the corresponding virtual address in the file is thus a
1243 single constant value for any one executable or shared
1244 object in a given process. This difference is the base
1245 address. One use of the base address is to relocate the
1246 memory image of the program during dynamic linking.
1248 The same language also appears in Edition 4.0 of the System V
1249 ABI and is left unspecified in some of the earlier editions. */
1251 displacement = pc - exec_entry_point (exec_bfd, &exec_ops);
1254 new_offsets = xcalloc (symfile_objfile->num_sections,
1255 sizeof (struct section_offsets));
1256 old_chain = make_cleanup (xfree, new_offsets);
1258 for (i = 0; i < symfile_objfile->num_sections; i++)
1260 if (displacement != ANOFFSET (symfile_objfile->section_offsets, i))
1262 new_offsets->offsets[i] = displacement;
1266 objfile_relocate (symfile_objfile, new_offsets);
1268 do_cleanups (old_chain);
1276 svr4_solib_create_inferior_hook -- shared library startup support
1280 void svr4_solib_create_inferior_hook ()
1284 When gdb starts up the inferior, it nurses it along (through the
1285 shell) until it is ready to execute it's first instruction. At this
1286 point, this function gets called via expansion of the macro
1287 SOLIB_CREATE_INFERIOR_HOOK.
1289 For SunOS executables, this first instruction is typically the
1290 one at "_start", or a similar text label, regardless of whether
1291 the executable is statically or dynamically linked. The runtime
1292 startup code takes care of dynamically linking in any shared
1293 libraries, once gdb allows the inferior to continue.
1295 For SVR4 executables, this first instruction is either the first
1296 instruction in the dynamic linker (for dynamically linked
1297 executables) or the instruction at "start" for statically linked
1298 executables. For dynamically linked executables, the system
1299 first exec's /lib/libc.so.N, which contains the dynamic linker,
1300 and starts it running. The dynamic linker maps in any needed
1301 shared libraries, maps in the actual user executable, and then
1302 jumps to "start" in the user executable.
1304 For both SunOS shared libraries, and SVR4 shared libraries, we
1305 can arrange to cooperate with the dynamic linker to discover the
1306 names of shared libraries that are dynamically linked, and the
1307 base addresses to which they are linked.
1309 This function is responsible for discovering those names and
1310 addresses, and saving sufficient information about them to allow
1311 their symbols to be read at a later time.
1315 Between enable_break() and disable_break(), this code does not
1316 properly handle hitting breakpoints which the user might have
1317 set in the startup code or in the dynamic linker itself. Proper
1318 handling will probably have to wait until the implementation is
1319 changed to use the "breakpoint handler function" method.
1321 Also, what if child has exit()ed? Must exit loop somehow.
1325 svr4_solib_create_inferior_hook (void)
1327 /* Relocate the main executable if necessary. */
1328 svr4_relocate_main_executable ();
1330 if (!svr4_have_link_map_offsets ())
1333 if (!enable_break ())
1336 #if defined(_SCO_DS)
1337 /* SCO needs the loop below, other systems should be using the
1338 special shared library breakpoints and the shared library breakpoint
1341 Now run the target. It will eventually hit the breakpoint, at
1342 which point all of the libraries will have been mapped in and we
1343 can go groveling around in the dynamic linker structures to find
1344 out what we need to know about them. */
1346 clear_proceed_status ();
1347 stop_soon = STOP_QUIETLY;
1348 stop_signal = TARGET_SIGNAL_0;
1351 target_resume (pid_to_ptid (-1), 0, stop_signal);
1352 wait_for_inferior ();
1354 while (stop_signal != TARGET_SIGNAL_TRAP);
1355 stop_soon = NO_STOP_QUIETLY;
1356 #endif /* defined(_SCO_DS) */
1360 svr4_clear_solib (void)
1363 debug_loader_offset_p = 0;
1364 debug_loader_offset = 0;
1365 xfree (debug_loader_name);
1366 debug_loader_name = NULL;
1370 svr4_free_so (struct so_list *so)
1372 xfree (so->lm_info->lm);
1373 xfree (so->lm_info);
1377 /* Clear any bits of ADDR that wouldn't fit in a target-format
1378 data pointer. "Data pointer" here refers to whatever sort of
1379 address the dynamic linker uses to manage its sections. At the
1380 moment, we don't support shared libraries on any processors where
1381 code and data pointers are different sizes.
1383 This isn't really the right solution. What we really need here is
1384 a way to do arithmetic on CORE_ADDR values that respects the
1385 natural pointer/address correspondence. (For example, on the MIPS,
1386 converting a 32-bit pointer to a 64-bit CORE_ADDR requires you to
1387 sign-extend the value. There, simply truncating the bits above
1388 gdbarch_ptr_bit, as we do below, is no good.) This should probably
1389 be a new gdbarch method or something. */
1391 svr4_truncate_ptr (CORE_ADDR addr)
1393 if (gdbarch_ptr_bit (current_gdbarch) == sizeof (CORE_ADDR) * 8)
1394 /* We don't need to truncate anything, and the bit twiddling below
1395 will fail due to overflow problems. */
1398 return addr & (((CORE_ADDR) 1 << gdbarch_ptr_bit (current_gdbarch)) - 1);
1403 svr4_relocate_section_addresses (struct so_list *so,
1404 struct section_table *sec)
1406 sec->addr = svr4_truncate_ptr (sec->addr + LM_ADDR_CHECK (so,
1408 sec->endaddr = svr4_truncate_ptr (sec->endaddr + LM_ADDR_CHECK (so,
1413 /* Architecture-specific operations. */
1415 /* Per-architecture data key. */
1416 static struct gdbarch_data *solib_svr4_data;
1418 struct solib_svr4_ops
1420 /* Return a description of the layout of `struct link_map'. */
1421 struct link_map_offsets *(*fetch_link_map_offsets)(void);
1424 /* Return a default for the architecture-specific operations. */
1427 solib_svr4_init (struct obstack *obstack)
1429 struct solib_svr4_ops *ops;
1431 ops = OBSTACK_ZALLOC (obstack, struct solib_svr4_ops);
1432 ops->fetch_link_map_offsets = legacy_svr4_fetch_link_map_offsets_hook;
1436 /* Set the architecture-specific `struct link_map_offsets' fetcher for
1440 set_solib_svr4_fetch_link_map_offsets (struct gdbarch *gdbarch,
1441 struct link_map_offsets *(*flmo) (void))
1443 struct solib_svr4_ops *ops = gdbarch_data (gdbarch, solib_svr4_data);
1445 ops->fetch_link_map_offsets = flmo;
1448 /* Fetch a link_map_offsets structure using the architecture-specific
1449 `struct link_map_offsets' fetcher. */
1451 static struct link_map_offsets *
1452 svr4_fetch_link_map_offsets (void)
1454 struct solib_svr4_ops *ops = gdbarch_data (current_gdbarch, solib_svr4_data);
1456 gdb_assert (ops->fetch_link_map_offsets);
1457 return ops->fetch_link_map_offsets ();
1460 /* Return 1 if a link map offset fetcher has been defined, 0 otherwise. */
1463 svr4_have_link_map_offsets (void)
1465 struct solib_svr4_ops *ops = gdbarch_data (current_gdbarch, solib_svr4_data);
1466 return (ops->fetch_link_map_offsets != NULL);
1470 /* Most OS'es that have SVR4-style ELF dynamic libraries define a
1471 `struct r_debug' and a `struct link_map' that are binary compatible
1472 with the origional SVR4 implementation. */
1474 /* Fetch (and possibly build) an appropriate `struct link_map_offsets'
1475 for an ILP32 SVR4 system. */
1477 struct link_map_offsets *
1478 svr4_ilp32_fetch_link_map_offsets (void)
1480 static struct link_map_offsets lmo;
1481 static struct link_map_offsets *lmp = NULL;
1487 lmo.r_version_offset = 0;
1488 lmo.r_version_size = 4;
1489 lmo.r_map_offset = 4;
1490 lmo.r_ldsomap_offset = 20;
1492 /* Everything we need is in the first 20 bytes. */
1493 lmo.link_map_size = 20;
1494 lmo.l_addr_offset = 0;
1495 lmo.l_name_offset = 4;
1496 lmo.l_ld_offset = 8;
1497 lmo.l_next_offset = 12;
1498 lmo.l_prev_offset = 16;
1504 /* Fetch (and possibly build) an appropriate `struct link_map_offsets'
1505 for an LP64 SVR4 system. */
1507 struct link_map_offsets *
1508 svr4_lp64_fetch_link_map_offsets (void)
1510 static struct link_map_offsets lmo;
1511 static struct link_map_offsets *lmp = NULL;
1517 lmo.r_version_offset = 0;
1518 lmo.r_version_size = 4;
1519 lmo.r_map_offset = 8;
1520 lmo.r_ldsomap_offset = 40;
1522 /* Everything we need is in the first 40 bytes. */
1523 lmo.link_map_size = 40;
1524 lmo.l_addr_offset = 0;
1525 lmo.l_name_offset = 8;
1526 lmo.l_ld_offset = 16;
1527 lmo.l_next_offset = 24;
1528 lmo.l_prev_offset = 32;
1535 struct target_so_ops svr4_so_ops;
1537 /* Lookup global symbol for ELF DSOs linked with -Bsymbolic. Those DSOs have a
1538 different rule for symbol lookup. The lookup begins here in the DSO, not in
1539 the main executable. */
1541 static struct symbol *
1542 elf_lookup_lib_symbol (const struct objfile *objfile,
1544 const char *linkage_name,
1545 const domain_enum domain, struct symtab **symtab)
1547 if (objfile->obfd == NULL
1548 || scan_dyntag (DT_SYMBOLIC, objfile->obfd, NULL) != 1)
1551 return lookup_global_symbol_from_objfile
1552 (objfile, name, linkage_name, domain, symtab);
1555 extern initialize_file_ftype _initialize_svr4_solib; /* -Wmissing-prototypes */
1558 _initialize_svr4_solib (void)
1560 solib_svr4_data = gdbarch_data_register_pre_init (solib_svr4_init);
1562 svr4_so_ops.relocate_section_addresses = svr4_relocate_section_addresses;
1563 svr4_so_ops.free_so = svr4_free_so;
1564 svr4_so_ops.clear_solib = svr4_clear_solib;
1565 svr4_so_ops.solib_create_inferior_hook = svr4_solib_create_inferior_hook;
1566 svr4_so_ops.special_symbol_handling = svr4_special_symbol_handling;
1567 svr4_so_ops.current_sos = svr4_current_sos;
1568 svr4_so_ops.open_symbol_file_object = open_symbol_file_object;
1569 svr4_so_ops.in_dynsym_resolve_code = svr4_in_dynsym_resolve_code;
1570 svr4_so_ops.lookup_lib_global_symbol = elf_lookup_lib_symbol;
1572 /* FIXME: Don't do this here. *_gdbarch_init() should set so_ops. */
1573 current_target_so_ops = &svr4_so_ops;