| 1 | /* Reading symbol files from memory. |
| 2 | |
| 3 | Copyright (C) 1986-2019 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 | |
| 57 | /* Verify parameters of target_read_memory_bfd and target_read_memory are |
| 58 | compatible. */ |
| 59 | |
| 60 | gdb_static_assert (sizeof (CORE_ADDR) == sizeof (bfd_vma)); |
| 61 | gdb_static_assert (sizeof (gdb_byte) == sizeof (bfd_byte)); |
| 62 | gdb_static_assert (sizeof (ssize_t) <= sizeof (bfd_size_type)); |
| 63 | |
| 64 | /* Provide bfd/ compatible prototype for target_read_memory. Casting would not |
| 65 | be enough as LEN width may differ. */ |
| 66 | |
| 67 | static int |
| 68 | target_read_memory_bfd (bfd_vma memaddr, bfd_byte *myaddr, bfd_size_type len) |
| 69 | { |
| 70 | /* MYADDR must be already allocated for the LEN size so it has to fit in |
| 71 | ssize_t. */ |
| 72 | gdb_assert ((ssize_t) len == len); |
| 73 | |
| 74 | return target_read_memory (memaddr, myaddr, len); |
| 75 | } |
| 76 | |
| 77 | /* Read inferior memory at ADDR to find the header of a loaded object file |
| 78 | and read its in-core symbols out of inferior memory. SIZE, if |
| 79 | non-zero, is the known size of the object. TEMPL is a bfd |
| 80 | representing the target's format. NAME is the name to use for this |
| 81 | symbol file in messages; it can be NULL or a malloc-allocated string |
| 82 | which will be attached to the BFD. */ |
| 83 | static struct objfile * |
| 84 | symbol_file_add_from_memory (struct bfd *templ, CORE_ADDR addr, |
| 85 | size_t size, 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 = 0; |
| 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, |
| 97 | target_read_memory_bfd); |
| 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 = xstrdup ("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 | |
| 112 | section_addr_info sai; |
| 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, bfd_get_filename (nbfd), |
| 123 | add_flags, &sai, OBJF_SHARED, NULL); |
| 124 | |
| 125 | add_target_sections_of_objfile (objf); |
| 126 | |
| 127 | /* This might change our ideas about frames already looked at. */ |
| 128 | reinit_frame_cache (); |
| 129 | |
| 130 | return objf; |
| 131 | } |
| 132 | |
| 133 | |
| 134 | static void |
| 135 | add_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. */ |
| 146 | if (symfile_objfile != NULL) |
| 147 | templ = symfile_objfile->obfd; |
| 148 | else |
| 149 | templ = exec_bfd; |
| 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 | |
| 160 | static void |
| 161 | add_vsyscall_page (struct target_ops *target, int from_tty) |
| 162 | { |
| 163 | struct mem_range vsyscall_range; |
| 164 | |
| 165 | if (gdbarch_vsyscall_range (target_gdbarch (), &vsyscall_range)) |
| 166 | { |
| 167 | struct bfd *bfd; |
| 168 | |
| 169 | if (core_bfd != NULL) |
| 170 | bfd = core_bfd; |
| 171 | else if (exec_bfd != NULL) |
| 172 | bfd = exec_bfd; |
| 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 | char *name = xstrprintf ("system-supplied DSO at %s", |
| 187 | paddress (target_gdbarch (), vsyscall_range.start)); |
| 188 | try |
| 189 | { |
| 190 | /* Pass zero for FROM_TTY, because the action of loading the |
| 191 | vsyscall DSO was not triggered by the user, even if the |
| 192 | user typed "run" at the TTY. */ |
| 193 | symbol_file_add_from_memory (bfd, |
| 194 | vsyscall_range.start, |
| 195 | vsyscall_range.length, |
| 196 | name, |
| 197 | 0 /* from_tty */); |
| 198 | } |
| 199 | catch (const gdb_exception &ex) |
| 200 | { |
| 201 | exception_print (gdb_stderr, ex); |
| 202 | } |
| 203 | } |
| 204 | } |
| 205 | |
| 206 | void |
| 207 | _initialize_symfile_mem (void) |
| 208 | { |
| 209 | add_cmd ("add-symbol-file-from-memory", class_files, |
| 210 | add_symbol_file_from_memory_command, |
| 211 | _("Load the symbols out of memory from a " |
| 212 | "dynamically loaded object file.\n" |
| 213 | "Give an expression for the address " |
| 214 | "of the file's shared object file header."), |
| 215 | &cmdlist); |
| 216 | |
| 217 | /* Want to know of each new inferior so that its vsyscall info can |
| 218 | be extracted. */ |
| 219 | gdb::observers::inferior_created.attach (add_vsyscall_page); |
| 220 | } |