gdb/i386-obsd-tdep.c

   1 /* Target-dependent code for OpenBSD/i386.
   2
   3    Copyright (C) 1988-2020 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 #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 \f
 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 \f
 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 \f
 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 \f
 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 }