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 61 gdb_static_assert (sizeof (CORE_ADDR) >= sizeof (bfd_vma)); 62 gdb_static_assert (sizeof (gdb_byte) == sizeof (bfd_byte)); 63 gdb_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 68 static int 69 target_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. */ 83 static struct objfile * 84 symbol_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, 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 = "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_holder, bfd_get_filename (nbfd), 123 add_flags, &sai, OBJF_SHARED, NULL); 124 125 current_program_space->add_target_sections (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 (current_program_space->symfile_object_file != NULL) 147 templ = current_program_space->symfile_object_file->obfd.get (); 148 else 149 templ = current_program_space->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 (inferior *inf) 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) 172 bfd = current_program_space->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 std::string name = string_printf ("system-supplied DSO at %s", 187 paddress (target_gdbarch (), 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. */ 194 symbol_file_add_from_memory (bfd, 195 vsyscall_range.start, 196 vsyscall_range.length, 197 name.c_str (), 198 0 /* from_tty */); 199 } 200 catch (const gdb_exception &ex) 201 { 202 exception_print (gdb_stderr, ex); 203 } 204 } 205 } 206 207 void _initialize_symfile_mem (); 208 void 209 _initialize_symfile_mem () 210 { 211 add_cmd ("add-symbol-file-from-memory", class_files, 212 add_symbol_file_from_memory_command, 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. */ 221 gdb::observers::inferior_created.attach (add_vsyscall_page, "symfile-mem"); 222 } 223