| 1 | /* Target-dependent code for GNU/Linux running on i386's, for GDB. |
| 2 | |
| 3 | Copyright 2000, 2001, 2002 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 2 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, write to the Free Software |
| 19 | Foundation, Inc., 59 Temple Place - Suite 330, |
| 20 | Boston, MA 02111-1307, USA. */ |
| 21 | |
| 22 | #include "defs.h" |
| 23 | #include "gdbcore.h" |
| 24 | #include "frame.h" |
| 25 | #include "value.h" |
| 26 | #include "regcache.h" |
| 27 | #include "inferior.h" |
| 28 | |
| 29 | /* For i386_linux_skip_solib_resolver. */ |
| 30 | #include "symtab.h" |
| 31 | #include "symfile.h" |
| 32 | #include "objfiles.h" |
| 33 | |
| 34 | #include "solib-svr4.h" /* For struct link_map_offsets. */ |
| 35 | |
| 36 | #include "i386-tdep.h" |
| 37 | #include "i386-linux-tdep.h" |
| 38 | |
| 39 | /* Return the name of register REG. */ |
| 40 | |
| 41 | static const char * |
| 42 | i386_linux_register_name (int reg) |
| 43 | { |
| 44 | /* Deal with the extra "orig_eax" pseudo register. */ |
| 45 | if (reg == I386_LINUX_ORIG_EAX_REGNUM) |
| 46 | return "orig_eax"; |
| 47 | |
| 48 | return i386_register_name (reg); |
| 49 | } |
| 50 | \f |
| 51 | /* Recognizing signal handler frames. */ |
| 52 | |
| 53 | /* GNU/Linux has two flavors of signals. Normal signal handlers, and |
| 54 | "realtime" (RT) signals. The RT signals can provide additional |
| 55 | information to the signal handler if the SA_SIGINFO flag is set |
| 56 | when establishing a signal handler using `sigaction'. It is not |
| 57 | unlikely that future versions of GNU/Linux will support SA_SIGINFO |
| 58 | for normal signals too. */ |
| 59 | |
| 60 | /* When the i386 Linux kernel calls a signal handler and the |
| 61 | SA_RESTORER flag isn't set, the return address points to a bit of |
| 62 | code on the stack. This function returns whether the PC appears to |
| 63 | be within this bit of code. |
| 64 | |
| 65 | The instruction sequence for normal signals is |
| 66 | pop %eax |
| 67 | mov $0x77,%eax |
| 68 | int $0x80 |
| 69 | or 0x58 0xb8 0x77 0x00 0x00 0x00 0xcd 0x80. |
| 70 | |
| 71 | Checking for the code sequence should be somewhat reliable, because |
| 72 | the effect is to call the system call sigreturn. This is unlikely |
| 73 | to occur anywhere other than a signal trampoline. |
| 74 | |
| 75 | It kind of sucks that we have to read memory from the process in |
| 76 | order to identify a signal trampoline, but there doesn't seem to be |
| 77 | any other way. The PC_IN_SIGTRAMP macro in tm-linux.h arranges to |
| 78 | only call us if no function name could be identified, which should |
| 79 | be the case since the code is on the stack. |
| 80 | |
| 81 | Detection of signal trampolines for handlers that set the |
| 82 | SA_RESTORER flag is in general not possible. Unfortunately this is |
| 83 | what the GNU C Library has been doing for quite some time now. |
| 84 | However, as of version 2.1.2, the GNU C Library uses signal |
| 85 | trampolines (named __restore and __restore_rt) that are identical |
| 86 | to the ones used by the kernel. Therefore, these trampolines are |
| 87 | supported too. */ |
| 88 | |
| 89 | #define LINUX_SIGTRAMP_INSN0 (0x58) /* pop %eax */ |
| 90 | #define LINUX_SIGTRAMP_OFFSET0 (0) |
| 91 | #define LINUX_SIGTRAMP_INSN1 (0xb8) /* mov $NNNN,%eax */ |
| 92 | #define LINUX_SIGTRAMP_OFFSET1 (1) |
| 93 | #define LINUX_SIGTRAMP_INSN2 (0xcd) /* int */ |
| 94 | #define LINUX_SIGTRAMP_OFFSET2 (6) |
| 95 | |
| 96 | static const unsigned char linux_sigtramp_code[] = |
| 97 | { |
| 98 | LINUX_SIGTRAMP_INSN0, /* pop %eax */ |
| 99 | LINUX_SIGTRAMP_INSN1, 0x77, 0x00, 0x00, 0x00, /* mov $0x77,%eax */ |
| 100 | LINUX_SIGTRAMP_INSN2, 0x80 /* int $0x80 */ |
| 101 | }; |
| 102 | |
| 103 | #define LINUX_SIGTRAMP_LEN (sizeof linux_sigtramp_code) |
| 104 | |
| 105 | /* If PC is in a sigtramp routine, return the address of the start of |
| 106 | the routine. Otherwise, return 0. */ |
| 107 | |
| 108 | static CORE_ADDR |
| 109 | i386_linux_sigtramp_start (CORE_ADDR pc) |
| 110 | { |
| 111 | unsigned char buf[LINUX_SIGTRAMP_LEN]; |
| 112 | |
| 113 | /* We only recognize a signal trampoline if PC is at the start of |
| 114 | one of the three instructions. We optimize for finding the PC at |
| 115 | the start, as will be the case when the trampoline is not the |
| 116 | first frame on the stack. We assume that in the case where the |
| 117 | PC is not at the start of the instruction sequence, there will be |
| 118 | a few trailing readable bytes on the stack. */ |
| 119 | |
| 120 | if (read_memory_nobpt (pc, (char *) buf, LINUX_SIGTRAMP_LEN) != 0) |
| 121 | return 0; |
| 122 | |
| 123 | if (buf[0] != LINUX_SIGTRAMP_INSN0) |
| 124 | { |
| 125 | int adjust; |
| 126 | |
| 127 | switch (buf[0]) |
| 128 | { |
| 129 | case LINUX_SIGTRAMP_INSN1: |
| 130 | adjust = LINUX_SIGTRAMP_OFFSET1; |
| 131 | break; |
| 132 | case LINUX_SIGTRAMP_INSN2: |
| 133 | adjust = LINUX_SIGTRAMP_OFFSET2; |
| 134 | break; |
| 135 | default: |
| 136 | return 0; |
| 137 | } |
| 138 | |
| 139 | pc -= adjust; |
| 140 | |
| 141 | if (read_memory_nobpt (pc, (char *) buf, LINUX_SIGTRAMP_LEN) != 0) |
| 142 | return 0; |
| 143 | } |
| 144 | |
| 145 | if (memcmp (buf, linux_sigtramp_code, LINUX_SIGTRAMP_LEN) != 0) |
| 146 | return 0; |
| 147 | |
| 148 | return pc; |
| 149 | } |
| 150 | |
| 151 | /* This function does the same for RT signals. Here the instruction |
| 152 | sequence is |
| 153 | mov $0xad,%eax |
| 154 | int $0x80 |
| 155 | or 0xb8 0xad 0x00 0x00 0x00 0xcd 0x80. |
| 156 | |
| 157 | The effect is to call the system call rt_sigreturn. */ |
| 158 | |
| 159 | #define LINUX_RT_SIGTRAMP_INSN0 (0xb8) /* mov $NNNN,%eax */ |
| 160 | #define LINUX_RT_SIGTRAMP_OFFSET0 (0) |
| 161 | #define LINUX_RT_SIGTRAMP_INSN1 (0xcd) /* int */ |
| 162 | #define LINUX_RT_SIGTRAMP_OFFSET1 (5) |
| 163 | |
| 164 | static const unsigned char linux_rt_sigtramp_code[] = |
| 165 | { |
| 166 | LINUX_RT_SIGTRAMP_INSN0, 0xad, 0x00, 0x00, 0x00, /* mov $0xad,%eax */ |
| 167 | LINUX_RT_SIGTRAMP_INSN1, 0x80 /* int $0x80 */ |
| 168 | }; |
| 169 | |
| 170 | #define LINUX_RT_SIGTRAMP_LEN (sizeof linux_rt_sigtramp_code) |
| 171 | |
| 172 | /* If PC is in a RT sigtramp routine, return the address of the start |
| 173 | of the routine. Otherwise, return 0. */ |
| 174 | |
| 175 | static CORE_ADDR |
| 176 | i386_linux_rt_sigtramp_start (CORE_ADDR pc) |
| 177 | { |
| 178 | unsigned char buf[LINUX_RT_SIGTRAMP_LEN]; |
| 179 | |
| 180 | /* We only recognize a signal trampoline if PC is at the start of |
| 181 | one of the two instructions. We optimize for finding the PC at |
| 182 | the start, as will be the case when the trampoline is not the |
| 183 | first frame on the stack. We assume that in the case where the |
| 184 | PC is not at the start of the instruction sequence, there will be |
| 185 | a few trailing readable bytes on the stack. */ |
| 186 | |
| 187 | if (read_memory_nobpt (pc, (char *) buf, LINUX_RT_SIGTRAMP_LEN) != 0) |
| 188 | return 0; |
| 189 | |
| 190 | if (buf[0] != LINUX_RT_SIGTRAMP_INSN0) |
| 191 | { |
| 192 | if (buf[0] != LINUX_RT_SIGTRAMP_INSN1) |
| 193 | return 0; |
| 194 | |
| 195 | pc -= LINUX_RT_SIGTRAMP_OFFSET1; |
| 196 | |
| 197 | if (read_memory_nobpt (pc, (char *) buf, LINUX_RT_SIGTRAMP_LEN) != 0) |
| 198 | return 0; |
| 199 | } |
| 200 | |
| 201 | if (memcmp (buf, linux_rt_sigtramp_code, LINUX_RT_SIGTRAMP_LEN) != 0) |
| 202 | return 0; |
| 203 | |
| 204 | return pc; |
| 205 | } |
| 206 | |
| 207 | /* Return whether PC is in a GNU/Linux sigtramp routine. */ |
| 208 | |
| 209 | static int |
| 210 | i386_linux_pc_in_sigtramp (CORE_ADDR pc, char *name) |
| 211 | { |
| 212 | if (name) |
| 213 | return STREQ ("__restore", name) || STREQ ("__restore_rt", name); |
| 214 | |
| 215 | return (i386_linux_sigtramp_start (pc) != 0 |
| 216 | || i386_linux_rt_sigtramp_start (pc) != 0); |
| 217 | } |
| 218 | |
| 219 | /* Assuming FRAME is for a GNU/Linux sigtramp routine, return the |
| 220 | address of the associated sigcontext structure. */ |
| 221 | |
| 222 | static CORE_ADDR |
| 223 | i386_linux_sigcontext_addr (struct frame_info *frame) |
| 224 | { |
| 225 | CORE_ADDR pc; |
| 226 | |
| 227 | pc = i386_linux_sigtramp_start (frame->pc); |
| 228 | if (pc) |
| 229 | { |
| 230 | CORE_ADDR sp; |
| 231 | |
| 232 | if (frame->next) |
| 233 | /* If this isn't the top frame, the next frame must be for the |
| 234 | signal handler itself. The sigcontext structure lives on |
| 235 | the stack, right after the signum argument. */ |
| 236 | return frame->next->frame + 12; |
| 237 | |
| 238 | /* This is the top frame. We'll have to find the address of the |
| 239 | sigcontext structure by looking at the stack pointer. Keep |
| 240 | in mind that the first instruction of the sigtramp code is |
| 241 | "pop %eax". If the PC is at this instruction, adjust the |
| 242 | returned value accordingly. */ |
| 243 | sp = read_register (SP_REGNUM); |
| 244 | if (pc == frame->pc) |
| 245 | return sp + 4; |
| 246 | return sp; |
| 247 | } |
| 248 | |
| 249 | pc = i386_linux_rt_sigtramp_start (frame->pc); |
| 250 | if (pc) |
| 251 | { |
| 252 | if (frame->next) |
| 253 | /* If this isn't the top frame, the next frame must be for the |
| 254 | signal handler itself. The sigcontext structure is part of |
| 255 | the user context. A pointer to the user context is passed |
| 256 | as the third argument to the signal handler. */ |
| 257 | return read_memory_integer (frame->next->frame + 16, 4) + 20; |
| 258 | |
| 259 | /* This is the top frame. Again, use the stack pointer to find |
| 260 | the address of the sigcontext structure. */ |
| 261 | return read_memory_integer (read_register (SP_REGNUM) + 8, 4) + 20; |
| 262 | } |
| 263 | |
| 264 | error ("Couldn't recognize signal trampoline."); |
| 265 | return 0; |
| 266 | } |
| 267 | |
| 268 | /* Set the program counter for process PTID to PC. */ |
| 269 | |
| 270 | static void |
| 271 | i386_linux_write_pc (CORE_ADDR pc, ptid_t ptid) |
| 272 | { |
| 273 | write_register_pid (PC_REGNUM, pc, ptid); |
| 274 | |
| 275 | /* We must be careful with modifying the program counter. If we |
| 276 | just interrupted a system call, the kernel might try to restart |
| 277 | it when we resume the inferior. On restarting the system call, |
| 278 | the kernel will try backing up the program counter even though it |
| 279 | no longer points at the system call. This typically results in a |
| 280 | SIGSEGV or SIGILL. We can prevent this by writing `-1' in the |
| 281 | "orig_eax" pseudo-register. |
| 282 | |
| 283 | Note that "orig_eax" is saved when setting up a dummy call frame. |
| 284 | This means that it is properly restored when that frame is |
| 285 | popped, and that the interrupted system call will be restarted |
| 286 | when we resume the inferior on return from a function call from |
| 287 | within GDB. In all other cases the system call will not be |
| 288 | restarted. */ |
| 289 | write_register_pid (I386_LINUX_ORIG_EAX_REGNUM, -1, ptid); |
| 290 | } |
| 291 | \f |
| 292 | /* Calling functions in shared libraries. */ |
| 293 | |
| 294 | /* Find the minimal symbol named NAME, and return both the minsym |
| 295 | struct and its objfile. This probably ought to be in minsym.c, but |
| 296 | everything there is trying to deal with things like C++ and |
| 297 | SOFUN_ADDRESS_MAYBE_TURQUOISE, ... Since this is so simple, it may |
| 298 | be considered too special-purpose for general consumption. */ |
| 299 | |
| 300 | static struct minimal_symbol * |
| 301 | find_minsym_and_objfile (char *name, struct objfile **objfile_p) |
| 302 | { |
| 303 | struct objfile *objfile; |
| 304 | |
| 305 | ALL_OBJFILES (objfile) |
| 306 | { |
| 307 | struct minimal_symbol *msym; |
| 308 | |
| 309 | ALL_OBJFILE_MSYMBOLS (objfile, msym) |
| 310 | { |
| 311 | if (SYMBOL_NAME (msym) |
| 312 | && STREQ (SYMBOL_NAME (msym), name)) |
| 313 | { |
| 314 | *objfile_p = objfile; |
| 315 | return msym; |
| 316 | } |
| 317 | } |
| 318 | } |
| 319 | |
| 320 | return 0; |
| 321 | } |
| 322 | |
| 323 | static CORE_ADDR |
| 324 | skip_hurd_resolver (CORE_ADDR pc) |
| 325 | { |
| 326 | /* The HURD dynamic linker is part of the GNU C library, so many |
| 327 | GNU/Linux distributions use it. (All ELF versions, as far as I |
| 328 | know.) An unresolved PLT entry points to "_dl_runtime_resolve", |
| 329 | which calls "fixup" to patch the PLT, and then passes control to |
| 330 | the function. |
| 331 | |
| 332 | We look for the symbol `_dl_runtime_resolve', and find `fixup' in |
| 333 | the same objfile. If we are at the entry point of `fixup', then |
| 334 | we set a breakpoint at the return address (at the top of the |
| 335 | stack), and continue. |
| 336 | |
| 337 | It's kind of gross to do all these checks every time we're |
| 338 | called, since they don't change once the executable has gotten |
| 339 | started. But this is only a temporary hack --- upcoming versions |
| 340 | of GNU/Linux will provide a portable, efficient interface for |
| 341 | debugging programs that use shared libraries. */ |
| 342 | |
| 343 | struct objfile *objfile; |
| 344 | struct minimal_symbol *resolver |
| 345 | = find_minsym_and_objfile ("_dl_runtime_resolve", &objfile); |
| 346 | |
| 347 | if (resolver) |
| 348 | { |
| 349 | struct minimal_symbol *fixup |
| 350 | = lookup_minimal_symbol ("fixup", NULL, objfile); |
| 351 | |
| 352 | if (fixup && SYMBOL_VALUE_ADDRESS (fixup) == pc) |
| 353 | return (SAVED_PC_AFTER_CALL (get_current_frame ())); |
| 354 | } |
| 355 | |
| 356 | return 0; |
| 357 | } |
| 358 | |
| 359 | /* See the comments for SKIP_SOLIB_RESOLVER at the top of infrun.c. |
| 360 | This function: |
| 361 | 1) decides whether a PLT has sent us into the linker to resolve |
| 362 | a function reference, and |
| 363 | 2) if so, tells us where to set a temporary breakpoint that will |
| 364 | trigger when the dynamic linker is done. */ |
| 365 | |
| 366 | CORE_ADDR |
| 367 | i386_linux_skip_solib_resolver (CORE_ADDR pc) |
| 368 | { |
| 369 | CORE_ADDR result; |
| 370 | |
| 371 | /* Plug in functions for other kinds of resolvers here. */ |
| 372 | result = skip_hurd_resolver (pc); |
| 373 | if (result) |
| 374 | return result; |
| 375 | |
| 376 | return 0; |
| 377 | } |
| 378 | |
| 379 | /* Fetch (and possibly build) an appropriate link_map_offsets |
| 380 | structure for native GNU/Linux x86 targets using the struct offsets |
| 381 | defined in link.h (but without actual reference to that file). |
| 382 | |
| 383 | This makes it possible to access GNU/Linux x86 shared libraries |
| 384 | from a GDB that was not built on an GNU/Linux x86 host (for cross |
| 385 | debugging). */ |
| 386 | |
| 387 | static struct link_map_offsets * |
| 388 | i386_linux_svr4_fetch_link_map_offsets (void) |
| 389 | { |
| 390 | static struct link_map_offsets lmo; |
| 391 | static struct link_map_offsets *lmp = NULL; |
| 392 | |
| 393 | if (lmp == NULL) |
| 394 | { |
| 395 | lmp = &lmo; |
| 396 | |
| 397 | lmo.r_debug_size = 8; /* The actual size is 20 bytes, but |
| 398 | this is all we need. */ |
| 399 | lmo.r_map_offset = 4; |
| 400 | lmo.r_map_size = 4; |
| 401 | |
| 402 | lmo.link_map_size = 20; /* The actual size is 552 bytes, but |
| 403 | this is all we need. */ |
| 404 | lmo.l_addr_offset = 0; |
| 405 | lmo.l_addr_size = 4; |
| 406 | |
| 407 | lmo.l_name_offset = 4; |
| 408 | lmo.l_name_size = 4; |
| 409 | |
| 410 | lmo.l_next_offset = 12; |
| 411 | lmo.l_next_size = 4; |
| 412 | |
| 413 | lmo.l_prev_offset = 16; |
| 414 | lmo.l_prev_size = 4; |
| 415 | } |
| 416 | |
| 417 | return lmp; |
| 418 | } |
| 419 | \f |
| 420 | |
| 421 | static void |
| 422 | i386_linux_init_abi (struct gdbarch_info info, struct gdbarch *gdbarch) |
| 423 | { |
| 424 | struct gdbarch_tdep *tdep = gdbarch_tdep (gdbarch); |
| 425 | |
| 426 | /* GNU/Linux uses ELF. */ |
| 427 | i386_elf_init_abi (info, gdbarch); |
| 428 | |
| 429 | /* We support the SSE registers on GNU/Linux. */ |
| 430 | tdep->num_xmm_regs = I386_NUM_XREGS - 1; |
| 431 | /* set_gdbarch_num_regs (gdbarch, I386_SSE_NUM_REGS); */ |
| 432 | |
| 433 | /* Since we have the extra "orig_eax" register on GNU/Linux, we have |
| 434 | to adjust a few things. */ |
| 435 | |
| 436 | set_gdbarch_write_pc (gdbarch, i386_linux_write_pc); |
| 437 | set_gdbarch_num_regs (gdbarch, I386_SSE_NUM_REGS + 1); |
| 438 | set_gdbarch_register_name (gdbarch, i386_linux_register_name); |
| 439 | set_gdbarch_register_bytes (gdbarch, I386_SSE_SIZEOF_REGS + 4); |
| 440 | |
| 441 | tdep->jb_pc_offset = 20; /* From <bits/setjmp.h>. */ |
| 442 | |
| 443 | tdep->sigcontext_addr = i386_linux_sigcontext_addr; |
| 444 | tdep->sc_pc_offset = 14 * 4; /* From <asm/sigcontext.h>. */ |
| 445 | tdep->sc_sp_offset = 7 * 4; |
| 446 | |
| 447 | /* When the i386 Linux kernel calls a signal handler, the return |
| 448 | address points to a bit of code on the stack. This function is |
| 449 | used to identify this bit of code as a signal trampoline in order |
| 450 | to support backtracing through calls to signal handlers. */ |
| 451 | set_gdbarch_pc_in_sigtramp (gdbarch, i386_linux_pc_in_sigtramp); |
| 452 | |
| 453 | set_solib_svr4_fetch_link_map_offsets (gdbarch, |
| 454 | i386_linux_svr4_fetch_link_map_offsets); |
| 455 | } |
| 456 | |
| 457 | /* Provide a prototype to silence -Wmissing-prototypes. */ |
| 458 | extern void _initialize_i386_linux_tdep (void); |
| 459 | |
| 460 | void |
| 461 | _initialize_i386_linux_tdep (void) |
| 462 | { |
| 463 | gdbarch_register_osabi (bfd_arch_i386, GDB_OSABI_LINUX, |
| 464 | i386_linux_init_abi); |
| 465 | } |