1 /* Target-dependent code for OpenBSD/i386. 2 3 Copyright (C) 1988-2019 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 #include "defs.h" 21 #include "arch-utils.h" 22 #include "frame.h" 23 #include "frame-unwind.h" 24 #include "gdbcore.h" 25 #include "regcache.h" 26 #include "regset.h" 27 #include "symtab.h" 28 #include "objfiles.h" 29 #include "osabi.h" 30 #include "target.h" 31 #include "trad-frame.h" 32 33 #include "obsd-tdep.h" 34 #include "i386-tdep.h" 35 #include "i387-tdep.h" 36 #include "solib-svr4.h" 37 #include "bsd-uthread.h" 38 39 /* Support for signal handlers. */ 40 41 /* Since OpenBSD 3.2, the sigtramp routine is mapped at a random page 42 in virtual memory. The randomness makes it somewhat tricky to 43 detect it, but fortunately we can rely on the fact that the start 44 of the sigtramp routine is page-aligned. We recognize the 45 trampoline by looking for the code that invokes the sigreturn 46 system call. The offset where we can find that code varies from 47 release to release. 48 49 By the way, the mapping mentioned above is read-only, so you cannot 50 place a breakpoint in the signal trampoline. */ 51 52 /* Default page size. */ 53 static const int i386obsd_page_size = 4096; 54 55 /* Offset for sigreturn(2). */ 56 static const int i386obsd_sigreturn_offset[] = { 57 0x0a, /* OpenBSD 3.2 */ 58 0x14, /* OpenBSD 3.6 */ 59 0x3a, /* OpenBSD 3.8 */ 60 -1 61 }; 62 63 /* Return whether THIS_FRAME corresponds to an OpenBSD sigtramp 64 routine. */ 65 66 static int 67 i386obsd_sigtramp_p (struct frame_info *this_frame) 68 { 69 CORE_ADDR pc = get_frame_pc (this_frame); 70 CORE_ADDR start_pc = (pc & ~(i386obsd_page_size - 1)); 71 /* The call sequence invoking sigreturn(2). */ 72 const gdb_byte sigreturn[] = 73 { 74 0xb8, 75 0x67, 0x00, 0x00, 0x00, /* movl $SYS_sigreturn, %eax */ 76 0xcd, 0x80 /* int $0x80 */ 77 }; 78 size_t buflen = sizeof sigreturn; 79 const int *offset; 80 gdb_byte *buf; 81 const char *name; 82 83 /* If the function has a valid symbol name, it isn't a 84 trampoline. */ 85 find_pc_partial_function (pc, &name, NULL, NULL); 86 if (name != NULL) 87 return 0; 88 89 /* If the function lives in a valid section (even without a starting 90 point) it isn't a trampoline. */ 91 if (find_pc_section (pc) != NULL) 92 return 0; 93 94 /* Allocate buffer. */ 95 buf = (gdb_byte *) alloca (buflen); 96 97 /* Loop over all offsets. */ 98 for (offset = i386obsd_sigreturn_offset; *offset != -1; offset++) 99 { 100 /* If we can't read the instructions, return zero. */ 101 if (!safe_frame_unwind_memory (this_frame, start_pc + *offset, 102 buf, buflen)) 103 return 0; 104 105 /* Check for sigreturn(2). */ 106 if (memcmp (buf, sigreturn, buflen) == 0) 107 return 1; 108 } 109 110 return 0; 111 } 112 113 /* Mapping between the general-purpose registers in `struct reg' 114 format and GDB's register cache layout. */ 115 116 /* From <machine/reg.h>. */ 117 static int i386obsd_r_reg_offset[] = 118 { 119 0 * 4, /* %eax */ 120 1 * 4, /* %ecx */ 121 2 * 4, /* %edx */ 122 3 * 4, /* %ebx */ 123 4 * 4, /* %esp */ 124 5 * 4, /* %ebp */ 125 6 * 4, /* %esi */ 126 7 * 4, /* %edi */ 127 8 * 4, /* %eip */ 128 9 * 4, /* %eflags */ 129 10 * 4, /* %cs */ 130 11 * 4, /* %ss */ 131 12 * 4, /* %ds */ 132 13 * 4, /* %es */ 133 14 * 4, /* %fs */ 134 15 * 4 /* %gs */ 135 }; 136 137 138 139 /* Sigtramp routine location for OpenBSD 3.1 and earlier releases. */ 140 CORE_ADDR i386obsd_sigtramp_start_addr = 0xbfbfdf20; 141 CORE_ADDR i386obsd_sigtramp_end_addr = 0xbfbfdff0; 142 143 /* From <machine/signal.h>. */ 144 int i386obsd_sc_reg_offset[I386_NUM_GREGS] = 145 { 146 10 * 4, /* %eax */ 147 9 * 4, /* %ecx */ 148 8 * 4, /* %edx */ 149 7 * 4, /* %ebx */ 150 14 * 4, /* %esp */ 151 6 * 4, /* %ebp */ 152 5 * 4, /* %esi */ 153 4 * 4, /* %edi */ 154 11 * 4, /* %eip */ 155 13 * 4, /* %eflags */ 156 12 * 4, /* %cs */ 157 15 * 4, /* %ss */ 158 3 * 4, /* %ds */ 159 2 * 4, /* %es */ 160 1 * 4, /* %fs */ 161 0 * 4 /* %gs */ 162 }; 163 164 /* From /usr/src/lib/libpthread/arch/i386/uthread_machdep.c. */ 165 static int i386obsd_uthread_reg_offset[] = 166 { 167 11 * 4, /* %eax */ 168 10 * 4, /* %ecx */ 169 9 * 4, /* %edx */ 170 8 * 4, /* %ebx */ 171 -1, /* %esp */ 172 6 * 4, /* %ebp */ 173 5 * 4, /* %esi */ 174 4 * 4, /* %edi */ 175 12 * 4, /* %eip */ 176 -1, /* %eflags */ 177 13 * 4, /* %cs */ 178 -1, /* %ss */ 179 3 * 4, /* %ds */ 180 2 * 4, /* %es */ 181 1 * 4, /* %fs */ 182 0 * 4 /* %gs */ 183 }; 184 185 /* Offset within the thread structure where we can find the saved 186 stack pointer (%esp). */ 187 #define I386OBSD_UTHREAD_ESP_OFFSET 176 188 189 static void 190 i386obsd_supply_uthread (struct regcache *regcache, 191 int regnum, CORE_ADDR addr) 192 { 193 struct gdbarch *gdbarch = regcache->arch (); 194 enum bfd_endian byte_order = gdbarch_byte_order (gdbarch); 195 CORE_ADDR sp_addr = addr + I386OBSD_UTHREAD_ESP_OFFSET; 196 CORE_ADDR sp = 0; 197 gdb_byte buf[4]; 198 int i; 199 200 gdb_assert (regnum >= -1); 201 202 if (regnum == -1 || regnum == I386_ESP_REGNUM) 203 { 204 int offset; 205 206 /* Fetch stack pointer from thread structure. */ 207 sp = read_memory_unsigned_integer (sp_addr, 4, byte_order); 208 209 /* Adjust the stack pointer such that it looks as if we just 210 returned from _thread_machdep_switch. */ 211 offset = i386obsd_uthread_reg_offset[I386_EIP_REGNUM] + 4; 212 store_unsigned_integer (buf, 4, byte_order, sp + offset); 213 regcache->raw_supply (I386_ESP_REGNUM, buf); 214 } 215 216 for (i = 0; i < ARRAY_SIZE (i386obsd_uthread_reg_offset); i++) 217 { 218 if (i386obsd_uthread_reg_offset[i] != -1 219 && (regnum == -1 || regnum == i)) 220 { 221 /* Fetch stack pointer from thread structure (if we didn't 222 do so already). */ 223 if (sp == 0) 224 sp = read_memory_unsigned_integer (sp_addr, 4, byte_order); 225 226 /* Read the saved register from the stack frame. */ 227 read_memory (sp + i386obsd_uthread_reg_offset[i], buf, 4); 228 regcache->raw_supply (i, buf); 229 } 230 } 231 } 232 233 static void 234 i386obsd_collect_uthread (const struct regcache *regcache, 235 int regnum, CORE_ADDR addr) 236 { 237 struct gdbarch *gdbarch = regcache->arch (); 238 enum bfd_endian byte_order = gdbarch_byte_order (gdbarch); 239 CORE_ADDR sp_addr = addr + I386OBSD_UTHREAD_ESP_OFFSET; 240 CORE_ADDR sp = 0; 241 gdb_byte buf[4]; 242 int i; 243 244 gdb_assert (regnum >= -1); 245 246 if (regnum == -1 || regnum == I386_ESP_REGNUM) 247 { 248 int offset; 249 250 /* Calculate the stack pointer (frame pointer) that will be 251 stored into the thread structure. */ 252 offset = i386obsd_uthread_reg_offset[I386_EIP_REGNUM] + 4; 253 regcache->raw_collect (I386_ESP_REGNUM, buf); 254 sp = extract_unsigned_integer (buf, 4, byte_order) - offset; 255 256 /* Store the stack pointer. */ 257 write_memory_unsigned_integer (sp_addr, 4, byte_order, sp); 258 259 /* The stack pointer was (potentially) modified. Make sure we 260 build a proper stack frame. */ 261 regnum = -1; 262 } 263 264 for (i = 0; i < ARRAY_SIZE (i386obsd_uthread_reg_offset); i++) 265 { 266 if (i386obsd_uthread_reg_offset[i] != -1 267 && (regnum == -1 || regnum == i)) 268 { 269 /* Fetch stack pointer from thread structure (if we didn't 270 calculate it already). */ 271 if (sp == 0) 272 sp = read_memory_unsigned_integer (sp_addr, 4, byte_order); 273 274 /* Write the register into the stack frame. */ 275 regcache->raw_collect (i, buf); 276 write_memory (sp + i386obsd_uthread_reg_offset[i], buf, 4); 277 } 278 } 279 } 280 281 /* Kernel debugging support. */ 282 283 /* From <machine/frame.h>. Note that %esp and %ess are only saved in 284 a trap frame when entering the kernel from user space. */ 285 static int i386obsd_tf_reg_offset[] = 286 { 287 10 * 4, /* %eax */ 288 9 * 4, /* %ecx */ 289 8 * 4, /* %edx */ 290 7 * 4, /* %ebx */ 291 -1, /* %esp */ 292 6 * 4, /* %ebp */ 293 5 * 4, /* %esi */ 294 4 * 4, /* %edi */ 295 13 * 4, /* %eip */ 296 15 * 4, /* %eflags */ 297 14 * 4, /* %cs */ 298 -1, /* %ss */ 299 3 * 4, /* %ds */ 300 2 * 4, /* %es */ 301 0 * 4, /* %fs */ 302 1 * 4 /* %gs */ 303 }; 304 305 static struct trad_frame_cache * 306 i386obsd_trapframe_cache (struct frame_info *this_frame, void **this_cache) 307 { 308 struct gdbarch *gdbarch = get_frame_arch (this_frame); 309 enum bfd_endian byte_order = gdbarch_byte_order (gdbarch); 310 struct trad_frame_cache *cache; 311 CORE_ADDR func, sp, addr; 312 ULONGEST cs; 313 const char *name; 314 int i; 315 316 if (*this_cache) 317 return (struct trad_frame_cache *) *this_cache; 318 319 cache = trad_frame_cache_zalloc (this_frame); 320 *this_cache = cache; 321 322 func = get_frame_func (this_frame); 323 sp = get_frame_register_unsigned (this_frame, I386_ESP_REGNUM); 324 325 find_pc_partial_function (func, &name, NULL, NULL); 326 if (name && startswith (name, "Xintr")) 327 addr = sp + 8; /* It's an interrupt frame. */ 328 else 329 addr = sp; 330 331 for (i = 0; i < ARRAY_SIZE (i386obsd_tf_reg_offset); i++) 332 if (i386obsd_tf_reg_offset[i] != -1) 333 trad_frame_set_reg_addr (cache, i, addr + i386obsd_tf_reg_offset[i]); 334 335 /* Read %cs from trap frame. */ 336 addr += i386obsd_tf_reg_offset[I386_CS_REGNUM]; 337 cs = read_memory_unsigned_integer (addr, 4, byte_order); 338 if ((cs & I386_SEL_RPL) == I386_SEL_UPL) 339 { 340 /* Trap from user space; terminate backtrace. */ 341 trad_frame_set_id (cache, outer_frame_id); 342 } 343 else 344 { 345 /* Construct the frame ID using the function start. */ 346 trad_frame_set_id (cache, frame_id_build (sp + 8, func)); 347 } 348 349 return cache; 350 } 351 352 static void 353 i386obsd_trapframe_this_id (struct frame_info *this_frame, 354 void **this_cache, struct frame_id *this_id) 355 { 356 struct trad_frame_cache *cache = 357 i386obsd_trapframe_cache (this_frame, this_cache); 358 359 trad_frame_get_id (cache, this_id); 360 } 361 362 static struct value * 363 i386obsd_trapframe_prev_register (struct frame_info *this_frame, 364 void **this_cache, int regnum) 365 { 366 struct trad_frame_cache *cache = 367 i386obsd_trapframe_cache (this_frame, this_cache); 368 369 return trad_frame_get_register (cache, this_frame, regnum); 370 } 371 372 static int 373 i386obsd_trapframe_sniffer (const struct frame_unwind *self, 374 struct frame_info *this_frame, 375 void **this_prologue_cache) 376 { 377 ULONGEST cs; 378 const char *name; 379 380 /* Check Current Privilege Level and bail out if we're not executing 381 in kernel space. */ 382 cs = get_frame_register_unsigned (this_frame, I386_CS_REGNUM); 383 if ((cs & I386_SEL_RPL) == I386_SEL_UPL) 384 return 0; 385 386 find_pc_partial_function (get_frame_pc (this_frame), &name, NULL, NULL); 387 return (name && (strcmp (name, "calltrap") == 0 388 || strcmp (name, "syscall1") == 0 389 || startswith (name, "Xintr") 390 || startswith (name, "Xsoft"))); 391 } 392 393 static const struct frame_unwind i386obsd_trapframe_unwind = { 394 /* FIXME: kettenis/20051219: This really is more like an interrupt 395 frame, but SIGTRAMP_FRAME would print <signal handler called>, 396 which really is not what we want here. */ 397 NORMAL_FRAME, 398 default_frame_unwind_stop_reason, 399 i386obsd_trapframe_this_id, 400 i386obsd_trapframe_prev_register, 401 NULL, 402 i386obsd_trapframe_sniffer 403 }; 404 405 406 static void 407 i386obsd_init_abi (struct gdbarch_info info, struct gdbarch *gdbarch) 408 { 409 struct gdbarch_tdep *tdep = gdbarch_tdep (gdbarch); 410 411 /* Obviously OpenBSD is BSD-based. */ 412 i386bsd_init_abi (info, gdbarch); 413 obsd_init_abi (info, gdbarch); 414 i386_elf_init_abi (info, gdbarch); 415 416 /* OpenBSD has a different `struct reg'. */ 417 tdep->gregset_reg_offset = i386obsd_r_reg_offset; 418 tdep->gregset_num_regs = ARRAY_SIZE (i386obsd_r_reg_offset); 419 tdep->sizeof_gregset = 16 * 4; 420 421 /* OpenBSD uses -freg-struct-return by default. */ 422 tdep->struct_return = reg_struct_return; 423 424 /* OpenBSD uses a different memory layout. */ 425 tdep->sigtramp_start = i386obsd_sigtramp_start_addr; 426 tdep->sigtramp_end = i386obsd_sigtramp_end_addr; 427 tdep->sigtramp_p = i386obsd_sigtramp_p; 428 429 /* OpenBSD has a `struct sigcontext' that's different from the 430 original 4.3 BSD. */ 431 tdep->sc_reg_offset = i386obsd_sc_reg_offset; 432 tdep->sc_num_regs = ARRAY_SIZE (i386obsd_sc_reg_offset); 433 434 /* OpenBSD provides a user-level threads implementation. */ 435 bsd_uthread_set_supply_uthread (gdbarch, i386obsd_supply_uthread); 436 bsd_uthread_set_collect_uthread (gdbarch, i386obsd_collect_uthread); 437 438 /* Unwind kernel trap frames correctly. */ 439 frame_unwind_prepend_unwinder (gdbarch, &i386obsd_trapframe_unwind); 440 441 /* OpenBSD ELF uses SVR4-style shared libraries. */ 442 set_solib_svr4_fetch_link_map_offsets 443 (gdbarch, svr4_ilp32_fetch_link_map_offsets); 444 } 445 446 void 447 _initialize_i386obsd_tdep (void) 448 { 449 gdbarch_register_osabi (bfd_arch_i386, 0, GDB_OSABI_OPENBSD, 450 i386obsd_init_abi); 451 } 452