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symfile-mem.c
Go to the documentation of this file.
1/* Reading symbol files from memory.
2
3 Copyright (C) 1986-2023 Free Software Foundation, Inc.
4
5 This file is part of GDB.
6
7 This program is free software; you can redistribute it and/or modify
8 it under the terms of the GNU General Public License as published by
9 the Free Software Foundation; either version 3 of the License, or
10 (at your option) any later version.
11
12 This program is distributed in the hope that it will be useful,
13 but WITHOUT ANY WARRANTY; without even the implied warranty of
14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15 GNU General Public License for more details.
16
17 You should have received a copy of the GNU General Public License
18 along with this program. If not, see <http://www.gnu.org/licenses/>. */
19
20/* This file defines functions (and commands to exercise those
21 functions) for reading debugging information from object files
22 whose images are mapped directly into the inferior's memory. For
23 example, the Linux kernel maps a "syscall DSO" into each process's
24 address space; this DSO provides kernel-specific code for some
25 system calls.
26
27 At the moment, BFD only has functions for parsing object files from
28 memory for the ELF format, even though the general idea isn't
29 ELF-specific. This means that BFD only provides the functions GDB
30 needs when configured for ELF-based targets. So these functions
31 may only be compiled on ELF-based targets.
32
33 GDB has no idea whether it has been configured for an ELF-based
34 target or not: it just tries to handle whatever files it is given.
35 But this means there are no preprocessor symbols on which we could
36 make these functions' compilation conditional.
37
38 So, for the time being, we put these functions alone in this file,
39 and have .mt files reference them as appropriate. In the future, I
40 hope BFD will provide a format-independent bfd_from_remote_memory
41 entry point. */
42
43
44#include "defs.h"
45#include "symtab.h"
46#include "gdbcore.h"
47#include "objfiles.h"
48#include "gdbcmd.h"
49#include "target.h"
50#include "value.h"
51#include "symfile.h"
52#include "observable.h"
53#include "auxv.h"
54#include "elf/common.h"
55#include "gdb_bfd.h"
56#include "inferior.h"
57
58/* Verify parameters of target_read_memory_bfd and target_read_memory are
59 compatible. */
60
61gdb_static_assert (sizeof (CORE_ADDR) >= sizeof (bfd_vma));
62gdb_static_assert (sizeof (gdb_byte) == sizeof (bfd_byte));
63gdb_static_assert (sizeof (ssize_t) <= sizeof (bfd_size_type));
64
65/* Provide bfd/ compatible prototype for target_read_memory. Casting would not
66 be enough as LEN width may differ. */
67
68static int
69target_read_memory_bfd (bfd_vma memaddr, bfd_byte *myaddr, bfd_size_type len)
70{
71 /* MYADDR must be already allocated for the LEN size so it has to fit in
72 ssize_t. */
73 gdb_assert ((ssize_t) len == len);
74
75 return target_read_memory (memaddr, myaddr, len);
76}
77
78/* Read inferior memory at ADDR to find the header of a loaded object file
79 and read its in-core symbols out of inferior memory. SIZE, if
80 non-zero, is the known size of the object. TEMPL is a bfd
81 representing the target's format. NAME is the name to use for this
82 symbol file in messages; it can be NULL. */
83static struct objfile *
84symbol_file_add_from_memory (struct bfd *templ, CORE_ADDR addr,
85 size_t size, const char *name, int from_tty)
86{
87 struct objfile *objf;
88 struct bfd *nbfd;
89 struct bfd_section *sec;
90 bfd_vma loadbase;
91 symfile_add_flags add_flags = SYMFILE_NOT_FILENAME;
92
93 if (bfd_get_flavour (templ) != bfd_target_elf_flavour)
94 error (_("add-symbol-file-from-memory not supported for this target"));
95
96 nbfd = bfd_elf_bfd_from_remote_memory (templ, addr, size, &loadbase,
98 if (nbfd == NULL)
99 error (_("Failed to read a valid object file image from memory."));
100
101 /* Manage the new reference for the duration of this function. */
102 gdb_bfd_ref_ptr nbfd_holder = gdb_bfd_ref_ptr::new_reference (nbfd);
103
104 if (name == NULL)
105 name = "shared object read from target memory";
106 bfd_set_filename (nbfd, name);
107
108 if (!bfd_check_format (nbfd, bfd_object))
109 error (_("Got object file from memory but can't read symbols: %s."),
110 bfd_errmsg (bfd_get_error ()));
111
113 for (sec = nbfd->sections; sec != NULL; sec = sec->next)
114 if ((bfd_section_flags (sec) & (SEC_ALLOC|SEC_LOAD)) != 0)
115 sai.emplace_back (bfd_section_vma (sec) + loadbase,
116 bfd_section_name (sec),
117 sec->index);
118
119 if (from_tty)
120 add_flags |= SYMFILE_VERBOSE;
121
122 objf = symbol_file_add_from_bfd (nbfd_holder, bfd_get_filename (nbfd),
123 add_flags, &sai, OBJF_SHARED, NULL);
124
126
127 /* This might change our ideas about frames already looked at. */
129
130 return objf;
131}
132
133
134static void
135add_symbol_file_from_memory_command (const char *args, int from_tty)
136{
137 CORE_ADDR addr;
138 struct bfd *templ;
139
140 if (args == NULL)
141 error (_("add-symbol-file-from-memory requires an expression argument"));
142
143 addr = parse_and_eval_address (args);
144
145 /* We need some representative bfd to know the target we are looking at. */
148 else
150 if (templ == NULL)
151 error (_("Must use symbol-file or exec-file "
152 "before add-symbol-file-from-memory."));
153
154 symbol_file_add_from_memory (templ, addr, 0, NULL, from_tty);
155}
156
157/* Try to add the symbols for the vsyscall page, if there is one.
158 This function is called via the inferior_created observer. */
159
160static void
162{
163 struct mem_range vsyscall_range;
164
165 if (gdbarch_vsyscall_range (inf->gdbarch, &vsyscall_range))
166 {
167 struct bfd *bfd;
168
169 if (core_bfd != NULL)
170 bfd = core_bfd;
171 else if (current_program_space->exec_bfd () != NULL)
173 else
174 /* FIXME: cagney/2004-05-06: Should not require an existing
175 BFD when trying to create a run-time BFD of the VSYSCALL
176 page in the inferior. Unfortunately that's the current
177 interface so for the moment bail. Introducing a
178 ``bfd_runtime'' (a BFD created using the loaded image) file
179 format should fix this. */
180 {
181 warning (_("Could not load vsyscall page "
182 "because no executable was specified"));
183 return;
184 }
185
186 std::string name = string_printf ("system-supplied DSO at %s",
188 vsyscall_range.start));
189 try
190 {
191 /* Pass zero for FROM_TTY, because the action of loading the
192 vsyscall DSO was not triggered by the user, even if the
193 user typed "run" at the TTY. */
195 vsyscall_range.start,
196 vsyscall_range.length,
197 name.c_str (),
198 0 /* from_tty */);
199 }
200 catch (const gdb_exception_error &ex)
201 {
203 }
204 }
205}
206
208void
210{
211 add_cmd ("add-symbol-file-from-memory", class_files,
213 _("Load the symbols out of memory from a "
214 "dynamically loaded object file.\n"
215 "Give an expression for the address "
216 "of the file's shared object file header."),
217 &cmdlist);
218
219 /* Want to know of each new inferior so that its vsyscall info can
220 be extracted. */
222}
const char *const name
struct gdbarch * target_gdbarch(void)
struct cmd_list_element * cmdlist
Definition cli-cmds.c:87
struct cmd_list_element * add_cmd(const char *name, enum command_class theclass, const char *doc, struct cmd_list_element **list)
Definition cli-decode.c:233
@ class_files
Definition command.h:57
CORE_ADDR parse_and_eval_address(const char *exp)
Definition eval.c:52
void exception_print(struct ui_file *file, const struct gdb_exception &e)
Definition exceptions.c:106
void reinit_frame_cache(void)
Definition frame.c:2107
gdb::ref_ptr< struct bfd, gdb_bfd_ref_policy > gdb_bfd_ref_ptr
Definition gdb_bfd.h:79
int gdbarch_vsyscall_range(struct gdbarch *gdbarch, struct mem_range *range)
Definition gdbarch.c:5215
#define core_bfd
Definition gdbcore.h:130
size_t size
Definition go32-nat.c:239
observable< inferior * > inferior_created
@ OBJF_SHARED
struct program_space * current_program_space
Definition progspace.c:40
Definition gnu-nat.c:153
int length
Definition memrange.h:48
CORE_ADDR start
Definition memrange.h:45
gdb_bfd_ref_ptr obfd
Definition objfiles.h:740
void add_target_sections(void *owner, const target_section_table &sections)
Definition exec.c:602
bfd * exec_bfd() const
Definition progspace.h:268
struct objfile * symfile_object_file
Definition progspace.h:357
@ SYMFILE_NOT_FILENAME
@ SYMFILE_VERBOSE
static void add_symbol_file_from_memory_command(const char *args, int from_tty)
static int target_read_memory_bfd(bfd_vma memaddr, bfd_byte *myaddr, bfd_size_type len)
Definition symfile-mem.c:69
static void add_vsyscall_page(inferior *inf)
static struct objfile * symbol_file_add_from_memory(struct bfd *templ, CORE_ADDR addr, size_t size, const char *name, int from_tty)
Definition symfile-mem.c:84
void _initialize_symfile_mem()
gdb_static_assert(sizeof(CORE_ADDR) >=sizeof(bfd_vma))
struct objfile * symbol_file_add_from_bfd(const gdb_bfd_ref_ptr &abfd, const char *name, symfile_add_flags add_flags, section_addr_info *addrs, objfile_flags flags, struct objfile *parent)
Definition symfile.c:1155
std::vector< other_sections > section_addr_info
Definition symfile.h:74
int target_read_memory(CORE_ADDR memaddr, gdb_byte *myaddr, ssize_t len)
Definition target.c:1785
const char * paddress(struct gdbarch *gdbarch, CORE_ADDR addr)
Definition utils.c:3166
#define gdb_stderr
Definition utils.h:187