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 xfree (bfd_get_filename (nbfd)); 105 if (name == NULL) 106 nbfd->filename = xstrdup ("shared object read from target memory"); 107 else 108 nbfd->filename = name; 109 110 if (!bfd_check_format (nbfd, bfd_object)) 111 error (_("Got object file from memory but can't read symbols: %s."), 112 bfd_errmsg (bfd_get_error ())); 113 114 section_addr_info sai; 115 for (sec = nbfd->sections; sec != NULL; sec = sec->next) 116 if ((bfd_get_section_flags (nbfd, sec) & (SEC_ALLOC|SEC_LOAD)) != 0) 117 sai.emplace_back (bfd_get_section_vma (nbfd, sec) + loadbase, 118 bfd_get_section_name (nbfd, sec), 119 sec->index); 120 121 if (from_tty) 122 add_flags |= SYMFILE_VERBOSE; 123 124 objf = symbol_file_add_from_bfd (nbfd, bfd_get_filename (nbfd), 125 add_flags, &sai, OBJF_SHARED, NULL); 126 127 add_target_sections_of_objfile (objf); 128 129 /* This might change our ideas about frames already looked at. */ 130 reinit_frame_cache (); 131 132 return objf; 133 } 134 135 136 static void 137 add_symbol_file_from_memory_command (const char *args, int from_tty) 138 { 139 CORE_ADDR addr; 140 struct bfd *templ; 141 142 if (args == NULL) 143 error (_("add-symbol-file-from-memory requires an expression argument")); 144 145 addr = parse_and_eval_address (args); 146 147 /* We need some representative bfd to know the target we are looking at. */ 148 if (symfile_objfile != NULL) 149 templ = symfile_objfile->obfd; 150 else 151 templ = exec_bfd; 152 if (templ == NULL) 153 error (_("Must use symbol-file or exec-file " 154 "before add-symbol-file-from-memory.")); 155 156 symbol_file_add_from_memory (templ, addr, 0, NULL, from_tty); 157 } 158 159 /* Try to add the symbols for the vsyscall page, if there is one. 160 This function is called via the inferior_created observer. */ 161 162 static void 163 add_vsyscall_page (struct target_ops *target, int from_tty) 164 { 165 struct mem_range vsyscall_range; 166 167 if (gdbarch_vsyscall_range (target_gdbarch (), &vsyscall_range)) 168 { 169 struct bfd *bfd; 170 171 if (core_bfd != NULL) 172 bfd = core_bfd; 173 else if (exec_bfd != NULL) 174 bfd = exec_bfd; 175 else 176 /* FIXME: cagney/2004-05-06: Should not require an existing 177 BFD when trying to create a run-time BFD of the VSYSCALL 178 page in the inferior. Unfortunately that's the current 179 interface so for the moment bail. Introducing a 180 ``bfd_runtime'' (a BFD created using the loaded image) file 181 format should fix this. */ 182 { 183 warning (_("Could not load vsyscall page " 184 "because no executable was specified")); 185 return; 186 } 187 188 char *name = xstrprintf ("system-supplied DSO at %s", 189 paddress (target_gdbarch (), vsyscall_range.start)); 190 TRY 191 { 192 /* Pass zero for FROM_TTY, because the action of loading the 193 vsyscall DSO was not triggered by the user, even if the 194 user typed "run" at the TTY. */ 195 symbol_file_add_from_memory (bfd, 196 vsyscall_range.start, 197 vsyscall_range.length, 198 name, 199 0 /* from_tty */); 200 } 201 CATCH (ex, RETURN_MASK_ALL) 202 { 203 exception_print (gdb_stderr, ex); 204 } 205 END_CATCH 206 } 207 } 208 209 void 210 _initialize_symfile_mem (void) 211 { 212 add_cmd ("add-symbol-file-from-memory", class_files, 213 add_symbol_file_from_memory_command, 214 _("Load the symbols out of memory from a " 215 "dynamically loaded object file.\n" 216 "Give an expression for the address " 217 "of the file's shared object file header."), 218 &cmdlist); 219 220 /* Want to know of each new inferior so that its vsyscall info can 221 be extracted. */ 222 gdb::observers::inferior_created.attach (add_vsyscall_page); 223 } 224