1 /* Handle SVR4 shared libraries for GDB, the GNU Debugger.
3 Copyright 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1998, 1999,
4 2000, 2001, 2003, 2004, 2005
5 Free Software Foundation, Inc.
7 This file is part of GDB.
9 This program is free software; you can redistribute it and/or modify
10 it under the terms of the GNU General Public License as published by
11 the Free Software Foundation; either version 2 of the License, or
12 (at your option) any later version.
14 This program is distributed in the hope that it will be useful,
15 but WITHOUT ANY WARRANTY; without even the implied warranty of
16 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
17 GNU General Public License for more details.
19 You should have received a copy of the GNU General Public License
20 along with this program; if not, write to the Free Software
21 Foundation, Inc., 59 Temple Place - Suite 330,
22 Boston, MA 02111-1307, USA. */
26 #include "elf/external.h"
27 #include "elf/common.h"
38 #include "gdb_assert.h"
41 #include "solib-svr4.h"
43 #include "bfd-target.h"
46 static struct link_map_offsets *svr4_fetch_link_map_offsets (void);
47 static int svr4_have_link_map_offsets (void);
49 /* This hook is set to a function that provides native link map
50 offsets if the code in solib-legacy.c is linked in. */
51 struct link_map_offsets *(*legacy_svr4_fetch_link_map_offsets_hook) (void);
53 /* Link map info to include in an allocated so_list entry */
57 /* Pointer to copy of link map from inferior. The type is char *
58 rather than void *, so that we may use byte offsets to find the
59 various fields without the need for a cast. */
63 /* On SVR4 systems, a list of symbols in the dynamic linker where
64 GDB can try to place a breakpoint to monitor shared library
67 If none of these symbols are found, or other errors occur, then
68 SVR4 systems will fall back to using a symbol as the "startup
69 mapping complete" breakpoint address. */
71 static char *solib_break_names[] =
79 /* On the 64-bit PowerPC, the linker symbol with the same name as
80 the C function points to a function descriptor, not to the entry
81 point. The linker symbol whose name is the C function name
82 prefixed with a '.' points to the function's entry point. So
83 when we look through this table, we ignore symbols that point
84 into the data section (thus skipping the descriptor's symbol),
85 and eventually try this one, giving us the real entry point
92 #define BKPT_AT_SYMBOL 1
94 #if defined (BKPT_AT_SYMBOL)
95 static char *bkpt_names[] =
97 #ifdef SOLIB_BKPT_NAME
98 SOLIB_BKPT_NAME, /* Prefer configured name if it exists. */
107 static char *main_name_list[] =
113 /* Macro to extract an address from a solib structure. When GDB is
114 configured for some 32-bit targets (e.g. Solaris 2.7 sparc), BFD is
115 configured to handle 64-bit targets, so CORE_ADDR is 64 bits. We
116 have to extract only the significant bits of addresses to get the
117 right address when accessing the core file BFD.
119 Assume that the address is unsigned. */
121 #define SOLIB_EXTRACT_ADDRESS(MEMBER) \
122 extract_unsigned_integer (&(MEMBER), sizeof (MEMBER))
124 /* local data declarations */
126 /* link map access functions */
129 LM_ADDR (struct so_list *so)
131 struct link_map_offsets *lmo = svr4_fetch_link_map_offsets ();
133 return (CORE_ADDR) extract_signed_integer (so->lm_info->lm + lmo->l_addr_offset,
138 LM_NEXT (struct so_list *so)
140 struct link_map_offsets *lmo = svr4_fetch_link_map_offsets ();
142 /* Assume that the address is unsigned. */
143 return extract_unsigned_integer (so->lm_info->lm + lmo->l_next_offset,
148 LM_NAME (struct so_list *so)
150 struct link_map_offsets *lmo = svr4_fetch_link_map_offsets ();
152 /* Assume that the address is unsigned. */
153 return extract_unsigned_integer (so->lm_info->lm + lmo->l_name_offset,
158 IGNORE_FIRST_LINK_MAP_ENTRY (struct so_list *so)
160 struct link_map_offsets *lmo = svr4_fetch_link_map_offsets ();
162 /* Assume that the address is unsigned. */
163 return extract_unsigned_integer (so->lm_info->lm + lmo->l_prev_offset,
164 lmo->l_prev_size) == 0;
167 static CORE_ADDR debug_base; /* Base of dynamic linker structures */
168 static CORE_ADDR breakpoint_addr; /* Address where end bkpt is set */
170 /* Local function prototypes */
172 static int match_main (char *);
174 static CORE_ADDR bfd_lookup_symbol (bfd *, char *, flagword);
180 bfd_lookup_symbol -- lookup the value for a specific symbol
184 CORE_ADDR bfd_lookup_symbol (bfd *abfd, char *symname, flagword sect_flags)
188 An expensive way to lookup the value of a single symbol for
189 bfd's that are only temporary anyway. This is used by the
190 shared library support to find the address of the debugger
191 interface structures in the shared library.
193 If SECT_FLAGS is non-zero, only match symbols in sections whose
194 flags include all those in SECT_FLAGS.
196 Note that 0 is specifically allowed as an error return (no
201 bfd_lookup_symbol (bfd *abfd, char *symname, flagword sect_flags)
205 asymbol **symbol_table;
206 unsigned int number_of_symbols;
208 struct cleanup *back_to;
209 CORE_ADDR symaddr = 0;
211 storage_needed = bfd_get_symtab_upper_bound (abfd);
213 if (storage_needed > 0)
215 symbol_table = (asymbol **) xmalloc (storage_needed);
216 back_to = make_cleanup (xfree, symbol_table);
217 number_of_symbols = bfd_canonicalize_symtab (abfd, symbol_table);
219 for (i = 0; i < number_of_symbols; i++)
221 sym = *symbol_table++;
222 if (strcmp (sym->name, symname) == 0
223 && (sym->section->flags & sect_flags) == sect_flags)
225 /* Bfd symbols are section relative. */
226 symaddr = sym->value + sym->section->vma;
230 do_cleanups (back_to);
236 /* On FreeBSD, the dynamic linker is stripped by default. So we'll
237 have to check the dynamic string table too. */
239 storage_needed = bfd_get_dynamic_symtab_upper_bound (abfd);
241 if (storage_needed > 0)
243 symbol_table = (asymbol **) xmalloc (storage_needed);
244 back_to = make_cleanup (xfree, symbol_table);
245 number_of_symbols = bfd_canonicalize_dynamic_symtab (abfd, symbol_table);
247 for (i = 0; i < number_of_symbols; i++)
249 sym = *symbol_table++;
251 if (strcmp (sym->name, symname) == 0
252 && (sym->section->flags & sect_flags) == sect_flags)
254 /* Bfd symbols are section relative. */
255 symaddr = sym->value + sym->section->vma;
259 do_cleanups (back_to);
269 elf_locate_base -- locate the base address of dynamic linker structs
270 for SVR4 elf targets.
274 CORE_ADDR elf_locate_base (void)
278 For SVR4 elf targets the address of the dynamic linker's runtime
279 structure is contained within the dynamic info section in the
280 executable file. The dynamic section is also mapped into the
281 inferior address space. Because the runtime loader fills in the
282 real address before starting the inferior, we have to read in the
283 dynamic info section from the inferior address space.
284 If there are any errors while trying to find the address, we
285 silently return 0, otherwise the found address is returned.
290 elf_locate_base (void)
292 struct bfd_section *dyninfo_sect;
293 int dyninfo_sect_size;
294 CORE_ADDR dyninfo_addr;
299 /* Find the start address of the .dynamic section. */
300 dyninfo_sect = bfd_get_section_by_name (exec_bfd, ".dynamic");
301 if (dyninfo_sect == NULL)
303 dyninfo_addr = bfd_section_vma (exec_bfd, dyninfo_sect);
305 /* Read in .dynamic section, silently ignore errors. */
306 dyninfo_sect_size = bfd_section_size (exec_bfd, dyninfo_sect);
307 buf = alloca (dyninfo_sect_size);
308 if (target_read_memory (dyninfo_addr, buf, dyninfo_sect_size))
311 /* Find the DT_DEBUG entry in the the .dynamic section.
312 For mips elf we look for DT_MIPS_RLD_MAP, mips elf apparently has
313 no DT_DEBUG entries. */
315 arch_size = bfd_get_arch_size (exec_bfd);
316 if (arch_size == -1) /* failure */
321 for (bufend = buf + dyninfo_sect_size;
323 buf += sizeof (Elf32_External_Dyn))
325 Elf32_External_Dyn *x_dynp = (Elf32_External_Dyn *) buf;
329 dyn_tag = bfd_h_get_32 (exec_bfd, (bfd_byte *) x_dynp->d_tag);
330 if (dyn_tag == DT_NULL)
332 else if (dyn_tag == DT_DEBUG)
334 dyn_ptr = bfd_h_get_32 (exec_bfd,
335 (bfd_byte *) x_dynp->d_un.d_ptr);
338 else if (dyn_tag == DT_MIPS_RLD_MAP)
341 int pbuf_size = TARGET_PTR_BIT / HOST_CHAR_BIT;
343 pbuf = alloca (pbuf_size);
344 /* DT_MIPS_RLD_MAP contains a pointer to the address
345 of the dynamic link structure. */
346 dyn_ptr = bfd_h_get_32 (exec_bfd,
347 (bfd_byte *) x_dynp->d_un.d_ptr);
348 if (target_read_memory (dyn_ptr, pbuf, pbuf_size))
350 return extract_unsigned_integer (pbuf, pbuf_size);
354 else /* 64-bit elf */
356 for (bufend = buf + dyninfo_sect_size;
358 buf += sizeof (Elf64_External_Dyn))
360 Elf64_External_Dyn *x_dynp = (Elf64_External_Dyn *) buf;
364 dyn_tag = bfd_h_get_64 (exec_bfd, (bfd_byte *) x_dynp->d_tag);
365 if (dyn_tag == DT_NULL)
367 else if (dyn_tag == DT_DEBUG)
369 dyn_ptr = bfd_h_get_64 (exec_bfd,
370 (bfd_byte *) x_dynp->d_un.d_ptr);
373 else if (dyn_tag == DT_MIPS_RLD_MAP)
376 int pbuf_size = TARGET_PTR_BIT / HOST_CHAR_BIT;
378 pbuf = alloca (pbuf_size);
379 /* DT_MIPS_RLD_MAP contains a pointer to the address
380 of the dynamic link structure. */
381 dyn_ptr = bfd_h_get_64 (exec_bfd,
382 (bfd_byte *) x_dynp->d_un.d_ptr);
383 if (target_read_memory (dyn_ptr, pbuf, pbuf_size))
385 return extract_unsigned_integer (pbuf, pbuf_size);
390 /* DT_DEBUG entry not found. */
398 locate_base -- locate the base address of dynamic linker structs
402 CORE_ADDR locate_base (void)
406 For both the SunOS and SVR4 shared library implementations, if the
407 inferior executable has been linked dynamically, there is a single
408 address somewhere in the inferior's data space which is the key to
409 locating all of the dynamic linker's runtime structures. This
410 address is the value of the debug base symbol. The job of this
411 function is to find and return that address, or to return 0 if there
412 is no such address (the executable is statically linked for example).
414 For SunOS, the job is almost trivial, since the dynamic linker and
415 all of it's structures are statically linked to the executable at
416 link time. Thus the symbol for the address we are looking for has
417 already been added to the minimal symbol table for the executable's
418 objfile at the time the symbol file's symbols were read, and all we
419 have to do is look it up there. Note that we explicitly do NOT want
420 to find the copies in the shared library.
422 The SVR4 version is a bit more complicated because the address
423 is contained somewhere in the dynamic info section. We have to go
424 to a lot more work to discover the address of the debug base symbol.
425 Because of this complexity, we cache the value we find and return that
426 value on subsequent invocations. Note there is no copy in the
427 executable symbol tables.
434 /* Check to see if we have a currently valid address, and if so, avoid
435 doing all this work again and just return the cached address. If
436 we have no cached address, try to locate it in the dynamic info
437 section for ELF executables. There's no point in doing any of this
438 though if we don't have some link map offsets to work with. */
440 if (debug_base == 0 && svr4_have_link_map_offsets ())
443 && bfd_get_flavour (exec_bfd) == bfd_target_elf_flavour)
444 debug_base = elf_locate_base ();
453 first_link_map_member -- locate first member in dynamic linker's map
457 static CORE_ADDR first_link_map_member (void)
461 Find the first element in the inferior's dynamic link map, and
462 return its address in the inferior. This function doesn't copy the
463 link map entry itself into our address space; current_sos actually
467 first_link_map_member (void)
470 struct link_map_offsets *lmo = svr4_fetch_link_map_offsets ();
471 gdb_byte *r_map_buf = xmalloc (lmo->r_map_size);
472 struct cleanup *cleanups = make_cleanup (xfree, r_map_buf);
474 read_memory (debug_base + lmo->r_map_offset, r_map_buf, lmo->r_map_size);
476 /* Assume that the address is unsigned. */
477 lm = extract_unsigned_integer (r_map_buf, lmo->r_map_size);
479 /* FIXME: Perhaps we should validate the info somehow, perhaps by
480 checking r_version for a known version number, or r_state for
483 do_cleanups (cleanups);
492 open_symbol_file_object
496 void open_symbol_file_object (void *from_tty)
500 If no open symbol file, attempt to locate and open the main symbol
501 file. On SVR4 systems, this is the first link map entry. If its
502 name is here, we can open it. Useful when attaching to a process
503 without first loading its symbol file.
505 If FROM_TTYP dereferences to a non-zero integer, allow messages to
506 be printed. This parameter is a pointer rather than an int because
507 open_symbol_file_object() is called via catch_errors() and
508 catch_errors() requires a pointer argument. */
511 open_symbol_file_object (void *from_ttyp)
513 CORE_ADDR lm, l_name;
516 int from_tty = *(int *)from_ttyp;
517 struct link_map_offsets *lmo = svr4_fetch_link_map_offsets ();
518 gdb_byte *l_name_buf = xmalloc (lmo->l_name_size);
519 struct cleanup *cleanups = make_cleanup (xfree, l_name_buf);
522 if (!query ("Attempt to reload symbols from process? "))
525 if ((debug_base = locate_base ()) == 0)
526 return 0; /* failed somehow... */
528 /* First link map member should be the executable. */
529 if ((lm = first_link_map_member ()) == 0)
530 return 0; /* failed somehow... */
532 /* Read address of name from target memory to GDB. */
533 read_memory (lm + lmo->l_name_offset, l_name_buf, lmo->l_name_size);
535 /* Convert the address to host format. Assume that the address is
537 l_name = extract_unsigned_integer (l_name_buf, lmo->l_name_size);
539 /* Free l_name_buf. */
540 do_cleanups (cleanups);
543 return 0; /* No filename. */
545 /* Now fetch the filename from target memory. */
546 target_read_string (l_name, &filename, SO_NAME_MAX_PATH_SIZE - 1, &errcode);
550 warning (_("failed to read exec filename from attached file: %s"),
551 safe_strerror (errcode));
555 make_cleanup (xfree, filename);
556 /* Have a pathname: read the symbol file. */
557 symbol_file_add_main (filename, from_tty);
564 current_sos -- build a list of currently loaded shared objects
568 struct so_list *current_sos ()
572 Build a list of `struct so_list' objects describing the shared
573 objects currently loaded in the inferior. This list does not
574 include an entry for the main executable file.
576 Note that we only gather information directly available from the
577 inferior --- we don't examine any of the shared library files
578 themselves. The declaration of `struct so_list' says which fields
579 we provide values for. */
581 static struct so_list *
582 svr4_current_sos (void)
585 struct so_list *head = 0;
586 struct so_list **link_ptr = &head;
588 /* Make sure we've looked up the inferior's dynamic linker's base
592 debug_base = locate_base ();
594 /* If we can't find the dynamic linker's base structure, this
595 must not be a dynamically linked executable. Hmm. */
600 /* Walk the inferior's link map list, and build our list of
601 `struct so_list' nodes. */
602 lm = first_link_map_member ();
605 struct link_map_offsets *lmo = svr4_fetch_link_map_offsets ();
607 = (struct so_list *) xmalloc (sizeof (struct so_list));
608 struct cleanup *old_chain = make_cleanup (xfree, new);
610 memset (new, 0, sizeof (*new));
612 new->lm_info = xmalloc (sizeof (struct lm_info));
613 make_cleanup (xfree, new->lm_info);
615 new->lm_info->lm = xmalloc (lmo->link_map_size);
616 make_cleanup (xfree, new->lm_info->lm);
617 memset (new->lm_info->lm, 0, lmo->link_map_size);
619 read_memory (lm, new->lm_info->lm, lmo->link_map_size);
623 /* For SVR4 versions, the first entry in the link map is for the
624 inferior executable, so we must ignore it. For some versions of
625 SVR4, it has no name. For others (Solaris 2.3 for example), it
626 does have a name, so we can no longer use a missing name to
627 decide when to ignore it. */
628 if (IGNORE_FIRST_LINK_MAP_ENTRY (new))
635 /* Extract this shared object's name. */
636 target_read_string (LM_NAME (new), &buffer,
637 SO_NAME_MAX_PATH_SIZE - 1, &errcode);
639 warning (_("Can't read pathname for load map: %s."),
640 safe_strerror (errcode));
643 strncpy (new->so_name, buffer, SO_NAME_MAX_PATH_SIZE - 1);
644 new->so_name[SO_NAME_MAX_PATH_SIZE - 1] = '\0';
646 strcpy (new->so_original_name, new->so_name);
649 /* If this entry has no name, or its name matches the name
650 for the main executable, don't include it in the list. */
651 if (! new->so_name[0]
652 || match_main (new->so_name))
658 link_ptr = &new->next;
662 discard_cleanups (old_chain);
668 /* Get the address of the link_map for a given OBJFILE. Loop through
669 the link maps, and return the address of the one corresponding to
670 the given objfile. Note that this function takes into account that
671 objfile can be the main executable, not just a shared library. The
672 main executable has always an empty name field in the linkmap. */
675 svr4_fetch_objfile_link_map (struct objfile *objfile)
679 if ((debug_base = locate_base ()) == 0)
680 return 0; /* failed somehow... */
682 /* Position ourselves on the first link map. */
683 lm = first_link_map_member ();
686 /* Get info on the layout of the r_debug and link_map structures. */
687 struct link_map_offsets *lmo = svr4_fetch_link_map_offsets ();
690 struct lm_info objfile_lm_info;
691 struct cleanup *old_chain;
692 CORE_ADDR name_address;
693 gdb_byte *l_name_buf = xmalloc (lmo->l_name_size);
694 old_chain = make_cleanup (xfree, l_name_buf);
696 /* Set up the buffer to contain the portion of the link_map
697 structure that gdb cares about. Note that this is not the
698 whole link_map structure. */
699 objfile_lm_info.lm = xmalloc (lmo->link_map_size);
700 make_cleanup (xfree, objfile_lm_info.lm);
701 memset (objfile_lm_info.lm, 0, lmo->link_map_size);
703 /* Read the link map into our internal structure. */
704 read_memory (lm, objfile_lm_info.lm, lmo->link_map_size);
706 /* Read address of name from target memory to GDB. */
707 read_memory (lm + lmo->l_name_offset, l_name_buf, lmo->l_name_size);
709 /* Extract this object's name. Assume that the address is
711 name_address = extract_unsigned_integer (l_name_buf, lmo->l_name_size);
712 target_read_string (name_address, &buffer,
713 SO_NAME_MAX_PATH_SIZE - 1, &errcode);
714 make_cleanup (xfree, buffer);
716 warning (_("Can't read pathname for load map: %s."),
717 safe_strerror (errcode));
720 /* Is this the linkmap for the file we want? */
721 /* If the file is not a shared library and has no name,
722 we are sure it is the main executable, so we return that. */
723 if ((buffer && strcmp (buffer, objfile->name) == 0)
724 || (!(objfile->flags & OBJF_SHARED) && (strcmp (buffer, "") == 0)))
726 do_cleanups (old_chain);
730 /* Not the file we wanted, continue checking. Assume that the
731 address is unsigned. */
732 lm = extract_unsigned_integer (objfile_lm_info.lm + lmo->l_next_offset,
734 do_cleanups (old_chain);
739 /* On some systems, the only way to recognize the link map entry for
740 the main executable file is by looking at its name. Return
741 non-zero iff SONAME matches one of the known main executable names. */
744 match_main (char *soname)
748 for (mainp = main_name_list; *mainp != NULL; mainp++)
750 if (strcmp (soname, *mainp) == 0)
757 /* Return 1 if PC lies in the dynamic symbol resolution code of the
758 SVR4 run time loader. */
759 static CORE_ADDR interp_text_sect_low;
760 static CORE_ADDR interp_text_sect_high;
761 static CORE_ADDR interp_plt_sect_low;
762 static CORE_ADDR interp_plt_sect_high;
765 svr4_in_dynsym_resolve_code (CORE_ADDR pc)
767 return ((pc >= interp_text_sect_low && pc < interp_text_sect_high)
768 || (pc >= interp_plt_sect_low && pc < interp_plt_sect_high)
769 || in_plt_section (pc, NULL));
772 /* Given an executable's ABFD and target, compute the entry-point
776 exec_entry_point (struct bfd *abfd, struct target_ops *targ)
778 /* KevinB wrote ... for most targets, the address returned by
779 bfd_get_start_address() is the entry point for the start
780 function. But, for some targets, bfd_get_start_address() returns
781 the address of a function descriptor from which the entry point
782 address may be extracted. This address is extracted by
783 gdbarch_convert_from_func_ptr_addr(). The method
784 gdbarch_convert_from_func_ptr_addr() is the merely the identify
785 function for targets which don't use function descriptors. */
786 return gdbarch_convert_from_func_ptr_addr (current_gdbarch,
787 bfd_get_start_address (abfd),
795 enable_break -- arrange for dynamic linker to hit breakpoint
799 int enable_break (void)
803 Both the SunOS and the SVR4 dynamic linkers have, as part of their
804 debugger interface, support for arranging for the inferior to hit
805 a breakpoint after mapping in the shared libraries. This function
806 enables that breakpoint.
808 For SunOS, there is a special flag location (in_debugger) which we
809 set to 1. When the dynamic linker sees this flag set, it will set
810 a breakpoint at a location known only to itself, after saving the
811 original contents of that place and the breakpoint address itself,
812 in it's own internal structures. When we resume the inferior, it
813 will eventually take a SIGTRAP when it runs into the breakpoint.
814 We handle this (in a different place) by restoring the contents of
815 the breakpointed location (which is only known after it stops),
816 chasing around to locate the shared libraries that have been
817 loaded, then resuming.
819 For SVR4, the debugger interface structure contains a member (r_brk)
820 which is statically initialized at the time the shared library is
821 built, to the offset of a function (_r_debug_state) which is guaran-
822 teed to be called once before mapping in a library, and again when
823 the mapping is complete. At the time we are examining this member,
824 it contains only the unrelocated offset of the function, so we have
825 to do our own relocation. Later, when the dynamic linker actually
826 runs, it relocates r_brk to be the actual address of _r_debug_state().
828 The debugger interface structure also contains an enumeration which
829 is set to either RT_ADD or RT_DELETE prior to changing the mapping,
830 depending upon whether or not the library is being mapped or unmapped,
831 and then set to RT_CONSISTENT after the library is mapped/unmapped.
839 #ifdef BKPT_AT_SYMBOL
841 struct minimal_symbol *msymbol;
843 asection *interp_sect;
845 /* First, remove all the solib event breakpoints. Their addresses
846 may have changed since the last time we ran the program. */
847 remove_solib_event_breakpoints ();
849 interp_text_sect_low = interp_text_sect_high = 0;
850 interp_plt_sect_low = interp_plt_sect_high = 0;
852 /* Find the .interp section; if not found, warn the user and drop
853 into the old breakpoint at symbol code. */
854 interp_sect = bfd_get_section_by_name (exec_bfd, ".interp");
857 unsigned int interp_sect_size;
859 CORE_ADDR load_addr = 0;
860 int load_addr_found = 0;
863 struct target_ops *tmp_bfd_target;
865 char *tmp_pathname = NULL;
866 CORE_ADDR sym_addr = 0;
868 /* Read the contents of the .interp section into a local buffer;
869 the contents specify the dynamic linker this program uses. */
870 interp_sect_size = bfd_section_size (exec_bfd, interp_sect);
871 buf = alloca (interp_sect_size);
872 bfd_get_section_contents (exec_bfd, interp_sect,
873 buf, 0, interp_sect_size);
875 /* Now we need to figure out where the dynamic linker was
876 loaded so that we can load its symbols and place a breakpoint
877 in the dynamic linker itself.
879 This address is stored on the stack. However, I've been unable
880 to find any magic formula to find it for Solaris (appears to
881 be trivial on GNU/Linux). Therefore, we have to try an alternate
882 mechanism to find the dynamic linker's base address. */
884 tmp_fd = solib_open (buf, &tmp_pathname);
886 tmp_bfd = bfd_fdopenr (tmp_pathname, gnutarget, tmp_fd);
891 /* Make sure the dynamic linker's really a useful object. */
892 if (!bfd_check_format (tmp_bfd, bfd_object))
894 warning (_("Unable to grok dynamic linker %s as an object file"), buf);
899 /* Now convert the TMP_BFD into a target. That way target, as
900 well as BFD operations can be used. Note that closing the
901 target will also close the underlying bfd. */
902 tmp_bfd_target = target_bfd_reopen (tmp_bfd);
904 /* On a running target, we can get the dynamic linker's base
905 address from the shared library table. */
906 solib_add (NULL, 0, NULL, auto_solib_add);
907 so = master_so_list ();
910 if (strcmp (buf, so->so_original_name) == 0)
913 load_addr = LM_ADDR (so);
919 /* Otherwise we find the dynamic linker's base address by examining
920 the current pc (which should point at the entry point for the
921 dynamic linker) and subtracting the offset of the entry point. */
922 if (!load_addr_found)
923 load_addr = (read_pc ()
924 - exec_entry_point (tmp_bfd, tmp_bfd_target));
926 /* Record the relocated start and end address of the dynamic linker
927 text and plt section for svr4_in_dynsym_resolve_code. */
928 interp_sect = bfd_get_section_by_name (tmp_bfd, ".text");
931 interp_text_sect_low =
932 bfd_section_vma (tmp_bfd, interp_sect) + load_addr;
933 interp_text_sect_high =
934 interp_text_sect_low + bfd_section_size (tmp_bfd, interp_sect);
936 interp_sect = bfd_get_section_by_name (tmp_bfd, ".plt");
939 interp_plt_sect_low =
940 bfd_section_vma (tmp_bfd, interp_sect) + load_addr;
941 interp_plt_sect_high =
942 interp_plt_sect_low + bfd_section_size (tmp_bfd, interp_sect);
945 /* Now try to set a breakpoint in the dynamic linker. */
946 for (bkpt_namep = solib_break_names; *bkpt_namep != NULL; bkpt_namep++)
948 /* On ABI's that use function descriptors, there are usually
949 two linker symbols associated with each C function: one
950 pointing at the actual entry point of the machine code,
951 and one pointing at the function's descriptor. The
952 latter symbol has the same name as the C function.
954 What we're looking for here is the machine code entry
955 point, so we are only interested in symbols in code
957 sym_addr = bfd_lookup_symbol (tmp_bfd, *bkpt_namep, SEC_CODE);
962 /* We're done with both the temporary bfd and target. Remember,
963 closing the target closes the underlying bfd. */
964 target_close (tmp_bfd_target, 0);
968 create_solib_event_breakpoint (load_addr + sym_addr);
972 /* For whatever reason we couldn't set a breakpoint in the dynamic
973 linker. Warn and drop into the old code. */
975 warning (_("Unable to find dynamic linker breakpoint function.\nGDB will be unable to debug shared library initializers\nand track explicitly loaded dynamic code."));
978 /* Scan through the list of symbols, trying to look up the symbol and
979 set a breakpoint there. Terminate loop when we/if we succeed. */
982 for (bkpt_namep = bkpt_names; *bkpt_namep != NULL; bkpt_namep++)
984 msymbol = lookup_minimal_symbol (*bkpt_namep, NULL, symfile_objfile);
985 if ((msymbol != NULL) && (SYMBOL_VALUE_ADDRESS (msymbol) != 0))
987 create_solib_event_breakpoint (SYMBOL_VALUE_ADDRESS (msymbol));
992 /* Nothing good happened. */
995 #endif /* BKPT_AT_SYMBOL */
1004 special_symbol_handling -- additional shared library symbol handling
1008 void special_symbol_handling ()
1012 Once the symbols from a shared object have been loaded in the usual
1013 way, we are called to do any system specific symbol handling that
1016 For SunOS4, this consisted of grunging around in the dynamic
1017 linkers structures to find symbol definitions for "common" symbols
1018 and adding them to the minimal symbol table for the runtime common
1021 However, for SVR4, there's nothing to do.
1026 svr4_special_symbol_handling (void)
1030 /* Relocate the main executable. This function should be called upon
1031 stopping the inferior process at the entry point to the program.
1032 The entry point from BFD is compared to the PC and if they are
1033 different, the main executable is relocated by the proper amount.
1035 As written it will only attempt to relocate executables which
1036 lack interpreter sections. It seems likely that only dynamic
1037 linker executables will get relocated, though it should work
1038 properly for a position-independent static executable as well. */
1041 svr4_relocate_main_executable (void)
1043 asection *interp_sect;
1044 CORE_ADDR pc = read_pc ();
1046 /* Decide if the objfile needs to be relocated. As indicated above,
1047 we will only be here when execution is stopped at the beginning
1048 of the program. Relocation is necessary if the address at which
1049 we are presently stopped differs from the start address stored in
1050 the executable AND there's no interpreter section. The condition
1051 regarding the interpreter section is very important because if
1052 there *is* an interpreter section, execution will begin there
1053 instead. When there is an interpreter section, the start address
1054 is (presumably) used by the interpreter at some point to start
1055 execution of the program.
1057 If there is an interpreter, it is normal for it to be set to an
1058 arbitrary address at the outset. The job of finding it is
1059 handled in enable_break().
1061 So, to summarize, relocations are necessary when there is no
1062 interpreter section and the start address obtained from the
1063 executable is different from the address at which GDB is
1066 [ The astute reader will note that we also test to make sure that
1067 the executable in question has the DYNAMIC flag set. It is my
1068 opinion that this test is unnecessary (undesirable even). It
1069 was added to avoid inadvertent relocation of an executable
1070 whose e_type member in the ELF header is not ET_DYN. There may
1071 be a time in the future when it is desirable to do relocations
1072 on other types of files as well in which case this condition
1073 should either be removed or modified to accomodate the new file
1074 type. (E.g, an ET_EXEC executable which has been built to be
1075 position-independent could safely be relocated by the OS if
1076 desired. It is true that this violates the ABI, but the ABI
1077 has been known to be bent from time to time.) - Kevin, Nov 2000. ]
1080 interp_sect = bfd_get_section_by_name (exec_bfd, ".interp");
1081 if (interp_sect == NULL
1082 && (bfd_get_file_flags (exec_bfd) & DYNAMIC) != 0
1083 && (exec_entry_point (exec_bfd, &exec_ops) != pc))
1085 struct cleanup *old_chain;
1086 struct section_offsets *new_offsets;
1088 CORE_ADDR displacement;
1090 /* It is necessary to relocate the objfile. The amount to
1091 relocate by is simply the address at which we are stopped
1092 minus the starting address from the executable.
1094 We relocate all of the sections by the same amount. This
1095 behavior is mandated by recent editions of the System V ABI.
1096 According to the System V Application Binary Interface,
1097 Edition 4.1, page 5-5:
1099 ... Though the system chooses virtual addresses for
1100 individual processes, it maintains the segments' relative
1101 positions. Because position-independent code uses relative
1102 addressesing between segments, the difference between
1103 virtual addresses in memory must match the difference
1104 between virtual addresses in the file. The difference
1105 between the virtual address of any segment in memory and
1106 the corresponding virtual address in the file is thus a
1107 single constant value for any one executable or shared
1108 object in a given process. This difference is the base
1109 address. One use of the base address is to relocate the
1110 memory image of the program during dynamic linking.
1112 The same language also appears in Edition 4.0 of the System V
1113 ABI and is left unspecified in some of the earlier editions. */
1115 displacement = pc - exec_entry_point (exec_bfd, &exec_ops);
1118 new_offsets = xcalloc (symfile_objfile->num_sections,
1119 sizeof (struct section_offsets));
1120 old_chain = make_cleanup (xfree, new_offsets);
1122 for (i = 0; i < symfile_objfile->num_sections; i++)
1124 if (displacement != ANOFFSET (symfile_objfile->section_offsets, i))
1126 new_offsets->offsets[i] = displacement;
1130 objfile_relocate (symfile_objfile, new_offsets);
1132 do_cleanups (old_chain);
1140 svr4_solib_create_inferior_hook -- shared library startup support
1144 void svr4_solib_create_inferior_hook ()
1148 When gdb starts up the inferior, it nurses it along (through the
1149 shell) until it is ready to execute it's first instruction. At this
1150 point, this function gets called via expansion of the macro
1151 SOLIB_CREATE_INFERIOR_HOOK.
1153 For SunOS executables, this first instruction is typically the
1154 one at "_start", or a similar text label, regardless of whether
1155 the executable is statically or dynamically linked. The runtime
1156 startup code takes care of dynamically linking in any shared
1157 libraries, once gdb allows the inferior to continue.
1159 For SVR4 executables, this first instruction is either the first
1160 instruction in the dynamic linker (for dynamically linked
1161 executables) or the instruction at "start" for statically linked
1162 executables. For dynamically linked executables, the system
1163 first exec's /lib/libc.so.N, which contains the dynamic linker,
1164 and starts it running. The dynamic linker maps in any needed
1165 shared libraries, maps in the actual user executable, and then
1166 jumps to "start" in the user executable.
1168 For both SunOS shared libraries, and SVR4 shared libraries, we
1169 can arrange to cooperate with the dynamic linker to discover the
1170 names of shared libraries that are dynamically linked, and the
1171 base addresses to which they are linked.
1173 This function is responsible for discovering those names and
1174 addresses, and saving sufficient information about them to allow
1175 their symbols to be read at a later time.
1179 Between enable_break() and disable_break(), this code does not
1180 properly handle hitting breakpoints which the user might have
1181 set in the startup code or in the dynamic linker itself. Proper
1182 handling will probably have to wait until the implementation is
1183 changed to use the "breakpoint handler function" method.
1185 Also, what if child has exit()ed? Must exit loop somehow.
1189 svr4_solib_create_inferior_hook (void)
1191 /* Relocate the main executable if necessary. */
1192 svr4_relocate_main_executable ();
1194 if (!svr4_have_link_map_offsets ())
1196 warning (_("no shared library support for this OS / ABI"));
1201 if (!enable_break ())
1203 warning (_("shared library handler failed to enable breakpoint"));
1207 #if defined(_SCO_DS)
1208 /* SCO needs the loop below, other systems should be using the
1209 special shared library breakpoints and the shared library breakpoint
1212 Now run the target. It will eventually hit the breakpoint, at
1213 which point all of the libraries will have been mapped in and we
1214 can go groveling around in the dynamic linker structures to find
1215 out what we need to know about them. */
1217 clear_proceed_status ();
1218 stop_soon = STOP_QUIETLY;
1219 stop_signal = TARGET_SIGNAL_0;
1222 target_resume (pid_to_ptid (-1), 0, stop_signal);
1223 wait_for_inferior ();
1225 while (stop_signal != TARGET_SIGNAL_TRAP);
1226 stop_soon = NO_STOP_QUIETLY;
1227 #endif /* defined(_SCO_DS) */
1231 svr4_clear_solib (void)
1237 svr4_free_so (struct so_list *so)
1239 xfree (so->lm_info->lm);
1240 xfree (so->lm_info);
1244 /* Clear any bits of ADDR that wouldn't fit in a target-format
1245 data pointer. "Data pointer" here refers to whatever sort of
1246 address the dynamic linker uses to manage its sections. At the
1247 moment, we don't support shared libraries on any processors where
1248 code and data pointers are different sizes.
1250 This isn't really the right solution. What we really need here is
1251 a way to do arithmetic on CORE_ADDR values that respects the
1252 natural pointer/address correspondence. (For example, on the MIPS,
1253 converting a 32-bit pointer to a 64-bit CORE_ADDR requires you to
1254 sign-extend the value. There, simply truncating the bits above
1255 TARGET_PTR_BIT, as we do below, is no good.) This should probably
1256 be a new gdbarch method or something. */
1258 svr4_truncate_ptr (CORE_ADDR addr)
1260 if (TARGET_PTR_BIT == sizeof (CORE_ADDR) * 8)
1261 /* We don't need to truncate anything, and the bit twiddling below
1262 will fail due to overflow problems. */
1265 return addr & (((CORE_ADDR) 1 << TARGET_PTR_BIT) - 1);
1270 svr4_relocate_section_addresses (struct so_list *so,
1271 struct section_table *sec)
1273 sec->addr = svr4_truncate_ptr (sec->addr + LM_ADDR (so));
1274 sec->endaddr = svr4_truncate_ptr (sec->endaddr + LM_ADDR (so));
1278 /* Architecture-specific operations. */
1280 /* Per-architecture data key. */
1281 static struct gdbarch_data *solib_svr4_data;
1283 struct solib_svr4_ops
1285 /* Return a description of the layout of `struct link_map'. */
1286 struct link_map_offsets *(*fetch_link_map_offsets)(void);
1289 /* Return a default for the architecture-specific operations. */
1292 solib_svr4_init (struct obstack *obstack)
1294 struct solib_svr4_ops *ops;
1296 ops = OBSTACK_ZALLOC (obstack, struct solib_svr4_ops);
1297 ops->fetch_link_map_offsets = legacy_svr4_fetch_link_map_offsets_hook;
1301 /* Set the architecture-specific `struct link_map_offsets' fetcher for
1305 set_solib_svr4_fetch_link_map_offsets (struct gdbarch *gdbarch,
1306 struct link_map_offsets *(*flmo) (void))
1308 struct solib_svr4_ops *ops = gdbarch_data (gdbarch, solib_svr4_data);
1310 ops->fetch_link_map_offsets = flmo;
1313 /* Fetch a link_map_offsets structure using the architecture-specific
1314 `struct link_map_offsets' fetcher. */
1316 static struct link_map_offsets *
1317 svr4_fetch_link_map_offsets (void)
1319 struct solib_svr4_ops *ops = gdbarch_data (current_gdbarch, solib_svr4_data);
1321 gdb_assert (ops->fetch_link_map_offsets);
1322 return ops->fetch_link_map_offsets ();
1325 /* Return 1 if a link map offset fetcher has been defined, 0 otherwise. */
1328 svr4_have_link_map_offsets (void)
1330 struct solib_svr4_ops *ops = gdbarch_data (current_gdbarch, solib_svr4_data);
1331 return (ops->fetch_link_map_offsets != NULL);
1335 /* Most OS'es that have SVR4-style ELF dynamic libraries define a
1336 `struct r_debug' and a `struct link_map' that are binary compatible
1337 with the origional SVR4 implementation. */
1339 /* Fetch (and possibly build) an appropriate `struct link_map_offsets'
1340 for an ILP32 SVR4 system. */
1342 struct link_map_offsets *
1343 svr4_ilp32_fetch_link_map_offsets (void)
1345 static struct link_map_offsets lmo;
1346 static struct link_map_offsets *lmp = NULL;
1352 /* Everything we need is in the first 8 bytes. */
1353 lmo.r_debug_size = 8;
1354 lmo.r_map_offset = 4;
1357 /* Everything we need is in the first 20 bytes. */
1358 lmo.link_map_size = 20;
1359 lmo.l_addr_offset = 0;
1360 lmo.l_addr_size = 4;
1361 lmo.l_name_offset = 4;
1362 lmo.l_name_size = 4;
1363 lmo.l_next_offset = 12;
1364 lmo.l_next_size = 4;
1365 lmo.l_prev_offset = 16;
1366 lmo.l_prev_size = 4;
1372 /* Fetch (and possibly build) an appropriate `struct link_map_offsets'
1373 for an LP64 SVR4 system. */
1375 struct link_map_offsets *
1376 svr4_lp64_fetch_link_map_offsets (void)
1378 static struct link_map_offsets lmo;
1379 static struct link_map_offsets *lmp = NULL;
1385 /* Everything we need is in the first 16 bytes. */
1386 lmo.r_debug_size = 16;
1387 lmo.r_map_offset = 8;
1390 /* Everything we need is in the first 40 bytes. */
1391 lmo.link_map_size = 40;
1392 lmo.l_addr_offset = 0;
1393 lmo.l_addr_size = 8;
1394 lmo.l_name_offset = 8;
1395 lmo.l_name_size = 8;
1396 lmo.l_next_offset = 24;
1397 lmo.l_next_size = 8;
1398 lmo.l_prev_offset = 32;
1399 lmo.l_prev_size = 8;
1406 static struct target_so_ops svr4_so_ops;
1408 extern initialize_file_ftype _initialize_svr4_solib; /* -Wmissing-prototypes */
1411 _initialize_svr4_solib (void)
1413 solib_svr4_data = gdbarch_data_register_pre_init (solib_svr4_init);
1415 svr4_so_ops.relocate_section_addresses = svr4_relocate_section_addresses;
1416 svr4_so_ops.free_so = svr4_free_so;
1417 svr4_so_ops.clear_solib = svr4_clear_solib;
1418 svr4_so_ops.solib_create_inferior_hook = svr4_solib_create_inferior_hook;
1419 svr4_so_ops.special_symbol_handling = svr4_special_symbol_handling;
1420 svr4_so_ops.current_sos = svr4_current_sos;
1421 svr4_so_ops.open_symbol_file_object = open_symbol_file_object;
1422 svr4_so_ops.in_dynsym_resolve_code = svr4_in_dynsym_resolve_code;
1424 /* FIXME: Don't do this here. *_gdbarch_init() should set so_ops. */
1425 current_target_so_ops = &svr4_so_ops;