1 /* Reading symbol files from memory. 2 3 Copyright (C) 1986-2020 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. */ 82 static struct objfile * 83 symbol_file_add_from_memory (struct bfd *templ, CORE_ADDR addr, 84 size_t size, const char *name, int from_tty) 85 { 86 struct objfile *objf; 87 struct bfd *nbfd; 88 struct bfd_section *sec; 89 bfd_vma loadbase; 90 symfile_add_flags add_flags = 0; 91 92 if (bfd_get_flavour (templ) != bfd_target_elf_flavour) 93 error (_("add-symbol-file-from-memory not supported for this target")); 94 95 nbfd = bfd_elf_bfd_from_remote_memory (templ, addr, size, &loadbase, 96 target_read_memory_bfd); 97 if (nbfd == NULL) 98 error (_("Failed to read a valid object file image from memory.")); 99 100 /* Manage the new reference for the duration of this function. */ 101 gdb_bfd_ref_ptr nbfd_holder = gdb_bfd_ref_ptr::new_reference (nbfd); 102 103 if (name == NULL) 104 name = "shared object read from target memory"; 105 bfd_set_filename (nbfd, name); 106 107 if (!bfd_check_format (nbfd, bfd_object)) 108 error (_("Got object file from memory but can't read symbols: %s."), 109 bfd_errmsg (bfd_get_error ())); 110 111 section_addr_info sai; 112 for (sec = nbfd->sections; sec != NULL; sec = sec->next) 113 if ((bfd_section_flags (sec) & (SEC_ALLOC|SEC_LOAD)) != 0) 114 sai.emplace_back (bfd_section_vma (sec) + loadbase, 115 bfd_section_name (sec), 116 sec->index); 117 118 if (from_tty) 119 add_flags |= SYMFILE_VERBOSE; 120 121 objf = symbol_file_add_from_bfd (nbfd, bfd_get_filename (nbfd), 122 add_flags, &sai, OBJF_SHARED, NULL); 123 124 add_target_sections_of_objfile (objf); 125 126 /* This might change our ideas about frames already looked at. */ 127 reinit_frame_cache (); 128 129 return objf; 130 } 131 132 133 static void 134 add_symbol_file_from_memory_command (const char *args, int from_tty) 135 { 136 CORE_ADDR addr; 137 struct bfd *templ; 138 139 if (args == NULL) 140 error (_("add-symbol-file-from-memory requires an expression argument")); 141 142 addr = parse_and_eval_address (args); 143 144 /* We need some representative bfd to know the target we are looking at. */ 145 if (symfile_objfile != NULL) 146 templ = symfile_objfile->obfd; 147 else 148 templ = exec_bfd; 149 if (templ == NULL) 150 error (_("Must use symbol-file or exec-file " 151 "before add-symbol-file-from-memory.")); 152 153 symbol_file_add_from_memory (templ, addr, 0, NULL, from_tty); 154 } 155 156 /* Try to add the symbols for the vsyscall page, if there is one. 157 This function is called via the inferior_created observer. */ 158 159 static void 160 add_vsyscall_page (struct target_ops *target, int from_tty) 161 { 162 struct mem_range vsyscall_range; 163 164 if (gdbarch_vsyscall_range (target_gdbarch (), &vsyscall_range)) 165 { 166 struct bfd *bfd; 167 168 if (core_bfd != NULL) 169 bfd = core_bfd; 170 else if (exec_bfd != NULL) 171 bfd = exec_bfd; 172 else 173 /* FIXME: cagney/2004-05-06: Should not require an existing 174 BFD when trying to create a run-time BFD of the VSYSCALL 175 page in the inferior. Unfortunately that's the current 176 interface so for the moment bail. Introducing a 177 ``bfd_runtime'' (a BFD created using the loaded image) file 178 format should fix this. */ 179 { 180 warning (_("Could not load vsyscall page " 181 "because no executable was specified")); 182 return; 183 } 184 185 std::string name = string_printf ("system-supplied DSO at %s", 186 paddress (target_gdbarch (), 187 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.c_str (), 197 0 /* from_tty */); 198 } 199 catch (const gdb_exception &ex) 200 { 201 exception_print (gdb_stderr, ex); 202 } 203 } 204 } 205 206 void _initialize_symfile_mem (); 207 void 208 _initialize_symfile_mem () 209 { 210 add_cmd ("add-symbol-file-from-memory", class_files, 211 add_symbol_file_from_memory_command, 212 _("Load the symbols out of memory from a " 213 "dynamically loaded object file.\n" 214 "Give an expression for the address " 215 "of the file's shared object file header."), 216 &cmdlist); 217 218 /* Want to know of each new inferior so that its vsyscall info can 219 be extracted. */ 220 gdb::observers::inferior_created.attach (add_vsyscall_page); 221 } 222