gdb/i386-obsd-tdep.c

   1 /* Target-dependent code for OpenBSD/i386.
   2
   3    Copyright (C) 1988-2024 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 "arch-utils.h"
  21 #include "frame.h"
  22 #include "frame-unwind.h"
  23 #include "gdbcore.h"
  24 #include "regcache.h"
  25 #include "regset.h"
  26 #include "symtab.h"
  27 #include "objfiles.h"
  28 #include "osabi.h"
  29 #include "target.h"
  30 #include "trad-frame.h"
  31
  32 #include "obsd-tdep.h"
  33 #include "i386-tdep.h"
  34 #include "i387-tdep.h"
  35 #include "solib-svr4.h"
  36 #include "bsd-uthread.h"
  37
  38 /* Support for signal handlers.  */
  39
  40 /* Since OpenBSD 3.2, the sigtramp routine is mapped at a random page
  41    in virtual memory.  The randomness makes it somewhat tricky to
  42    detect it, but fortunately we can rely on the fact that the start
  43    of the sigtramp routine is page-aligned.  We recognize the
  44    trampoline by looking for the code that invokes the sigreturn
  45    system call.  The offset where we can find that code varies from
  46    release to release.
  47
  48    By the way, the mapping mentioned above is read-only, so you cannot
  49    place a breakpoint in the signal trampoline.  */
  50
  51 /* Default page size.  */
  52 static const int i386obsd_page_size = 4096;
  53
  54 /* Offset for sigreturn(2).  */
  55 static const int i386obsd_sigreturn_offset[] = {
  56   0x0a,                         /* OpenBSD 3.2 */
  57   0x14,                         /* OpenBSD 3.6 */
  58   0x3a,                         /* OpenBSD 3.8 */
  59   -1
  60 };
  61
  62 /* Return whether THIS_FRAME corresponds to an OpenBSD sigtramp
  63    routine.  */
  64
  65 static int
  66 i386obsd_sigtramp_p (const frame_info_ptr &this_frame)
  67 {
  68   CORE_ADDR pc = get_frame_pc (this_frame);
  69   CORE_ADDR start_pc = (pc & ~(i386obsd_page_size - 1));
  70   /* The call sequence invoking sigreturn(2).  */
  71   const gdb_byte sigreturn[] =
  72   {
  73     0xb8,
  74     0x67, 0x00, 0x00, 0x00,     /* movl $SYS_sigreturn, %eax */
  75     0xcd, 0x80                  /* int $0x80 */
  76   };
  77   size_t buflen = sizeof sigreturn;
  78   const int *offset;
  79   gdb_byte *buf;
  80   const char *name;
  81
  82   /* If the function has a valid symbol name, it isn't a
  83      trampoline.  */
  84   find_pc_partial_function (pc, &name, NULL, NULL);
  85   if (name != NULL)
  86     return 0;
  87
  88   /* If the function lives in a valid section (even without a starting
  89      point) it isn't a trampoline.  */
  90   if (find_pc_section (pc) != NULL)
  91     return 0;
  92
  93   /* Allocate buffer.  */
  94   buf = (gdb_byte *) alloca (buflen);
  95
  96   /* Loop over all offsets.  */
  97   for (offset = i386obsd_sigreturn_offset; *offset != -1; offset++)
  98     {
  99       /* If we can't read the instructions, return zero.  */
 100       if (!safe_frame_unwind_memory (this_frame, start_pc + *offset,
 101                                      {buf, buflen}))
 102         return 0;
 103
 104       /* Check for sigreturn(2).  */
 105       if (memcmp (buf, sigreturn, buflen) == 0)
 106         return 1;
 107     }
 108
 109   return 0;
 110 }
 111 \f
 112 /* Mapping between the general-purpose registers in `struct reg'
 113    format and GDB's register cache layout.  */
 114
 115 /* From <machine/reg.h>.  */
 116 static int i386obsd_r_reg_offset[] =
 117 {
 118   0 * 4,                        /* %eax */
 119   1 * 4,                        /* %ecx */
 120   2 * 4,                        /* %edx */
 121   3 * 4,                        /* %ebx */
 122   4 * 4,                        /* %esp */
 123   5 * 4,                        /* %ebp */
 124   6 * 4,                        /* %esi */
 125   7 * 4,                        /* %edi */
 126   8 * 4,                        /* %eip */
 127   9 * 4,                        /* %eflags */
 128   10 * 4,                       /* %cs */
 129   11 * 4,                       /* %ss */
 130   12 * 4,                       /* %ds */
 131   13 * 4,                       /* %es */
 132   14 * 4,                       /* %fs */
 133   15 * 4                        /* %gs */
 134 };
 135
 136 \f
 137
 138 /* Sigtramp routine location for OpenBSD 3.1 and earlier releases.  */
 139 CORE_ADDR i386obsd_sigtramp_start_addr = 0xbfbfdf20;
 140 CORE_ADDR i386obsd_sigtramp_end_addr = 0xbfbfdff0;
 141
 142 /* From <machine/signal.h>.  */
 143 int i386obsd_sc_reg_offset[I386_NUM_GREGS] =
 144 {
 145   10 * 4,                       /* %eax */
 146   9 * 4,                        /* %ecx */
 147   8 * 4,                        /* %edx */
 148   7 * 4,                        /* %ebx */
 149   14 * 4,                       /* %esp */
 150   6 * 4,                        /* %ebp */
 151   5 * 4,                        /* %esi */
 152   4 * 4,                        /* %edi */
 153   11 * 4,                       /* %eip */
 154   13 * 4,                       /* %eflags */
 155   12 * 4,                       /* %cs */
 156   15 * 4,                       /* %ss */
 157   3 * 4,                        /* %ds */
 158   2 * 4,                        /* %es */
 159   1 * 4,                        /* %fs */
 160   0 * 4                         /* %gs */
 161 };
 162
 163 /* From /usr/src/lib/libpthread/arch/i386/uthread_machdep.c.  */
 164 static int i386obsd_uthread_reg_offset[] =
 165 {
 166   11 * 4,                       /* %eax */
 167   10 * 4,                       /* %ecx */
 168   9 * 4,                        /* %edx */
 169   8 * 4,                        /* %ebx */
 170   -1,                           /* %esp */
 171   6 * 4,                        /* %ebp */
 172   5 * 4,                        /* %esi */
 173   4 * 4,                        /* %edi */
 174   12 * 4,                       /* %eip */
 175   -1,                           /* %eflags */
 176   13 * 4,                       /* %cs */
 177   -1,                           /* %ss */
 178   3 * 4,                        /* %ds */
 179   2 * 4,                        /* %es */
 180   1 * 4,                        /* %fs */
 181   0 * 4                         /* %gs */
 182 };
 183
 184 /* Offset within the thread structure where we can find the saved
 185    stack pointer (%esp).  */
 186 #define I386OBSD_UTHREAD_ESP_OFFSET     176
 187
 188 static void
 189 i386obsd_supply_uthread (struct regcache *regcache,
 190                          int regnum, CORE_ADDR addr)
 191 {
 192   struct gdbarch *gdbarch = regcache->arch ();
 193   enum bfd_endian byte_order = gdbarch_byte_order (gdbarch);
 194   CORE_ADDR sp_addr = addr + I386OBSD_UTHREAD_ESP_OFFSET;
 195   CORE_ADDR sp = 0;
 196   gdb_byte buf[4];
 197   int i;
 198
 199   gdb_assert (regnum >= -1);
 200
 201   if (regnum == -1 || regnum == I386_ESP_REGNUM)
 202     {
 203       int offset;
 204
 205       /* Fetch stack pointer from thread structure.  */
 206       sp = read_memory_unsigned_integer (sp_addr, 4, byte_order);
 207
 208       /* Adjust the stack pointer such that it looks as if we just
 209          returned from _thread_machdep_switch.  */
 210       offset = i386obsd_uthread_reg_offset[I386_EIP_REGNUM] + 4;
 211       store_unsigned_integer (buf, 4, byte_order, sp + offset);
 212       regcache->raw_supply (I386_ESP_REGNUM, buf);
 213     }
 214
 215   for (i = 0; i < ARRAY_SIZE (i386obsd_uthread_reg_offset); i++)
 216     {
 217       if (i386obsd_uthread_reg_offset[i] != -1
 218           && (regnum == -1 || regnum == i))
 219         {
 220           /* Fetch stack pointer from thread structure (if we didn't
 221              do so already).  */
 222           if (sp == 0)
 223             sp = read_memory_unsigned_integer (sp_addr, 4, byte_order);
 224
 225           /* Read the saved register from the stack frame.  */
 226           read_memory (sp + i386obsd_uthread_reg_offset[i], buf, 4);
 227           regcache->raw_supply (i, buf);
 228         }
 229     }
 230 }
 231
 232 static void
 233 i386obsd_collect_uthread (const struct regcache *regcache,
 234                           int regnum, CORE_ADDR addr)
 235 {
 236   struct gdbarch *gdbarch = regcache->arch ();
 237   enum bfd_endian byte_order = gdbarch_byte_order (gdbarch);
 238   CORE_ADDR sp_addr = addr + I386OBSD_UTHREAD_ESP_OFFSET;
 239   CORE_ADDR sp = 0;
 240   gdb_byte buf[4];
 241   int i;
 242
 243   gdb_assert (regnum >= -1);
 244
 245   if (regnum == -1 || regnum == I386_ESP_REGNUM)
 246     {
 247       int offset;
 248
 249       /* Calculate the stack pointer (frame pointer) that will be
 250          stored into the thread structure.  */
 251       offset = i386obsd_uthread_reg_offset[I386_EIP_REGNUM] + 4;
 252       regcache->raw_collect (I386_ESP_REGNUM, buf);
 253       sp = extract_unsigned_integer (buf, 4, byte_order) - offset;
 254
 255       /* Store the stack pointer.  */
 256       write_memory_unsigned_integer (sp_addr, 4, byte_order, sp);
 257
 258       /* The stack pointer was (potentially) modified.  Make sure we
 259          build a proper stack frame.  */
 260       regnum = -1;
 261     }
 262
 263   for (i = 0; i < ARRAY_SIZE (i386obsd_uthread_reg_offset); i++)
 264     {
 265       if (i386obsd_uthread_reg_offset[i] != -1
 266           && (regnum == -1 || regnum == i))
 267         {
 268           /* Fetch stack pointer from thread structure (if we didn't
 269              calculate it already).  */
 270           if (sp == 0)
 271             sp = read_memory_unsigned_integer (sp_addr, 4, byte_order);
 272
 273           /* Write the register into the stack frame.  */
 274           regcache->raw_collect (i, buf);
 275           write_memory (sp + i386obsd_uthread_reg_offset[i], buf, 4);
 276         }
 277     }
 278 }
 279 \f
 280 /* Kernel debugging support.  */
 281
 282 /* From <machine/frame.h>.  Note that %esp and %ess are only saved in
 283    a trap frame when entering the kernel from user space.  */
 284 static int i386obsd_tf_reg_offset[] =
 285 {
 286   10 * 4,                       /* %eax */
 287   9 * 4,                        /* %ecx */
 288   8 * 4,                        /* %edx */
 289   7 * 4,                        /* %ebx */
 290   -1,                           /* %esp */
 291   6 * 4,                        /* %ebp */
 292   5 * 4,                        /* %esi */
 293   4 * 4,                        /* %edi */
 294   13 * 4,                       /* %eip */
 295   15 * 4,                       /* %eflags */
 296   14 * 4,                       /* %cs */
 297   -1,                           /* %ss */
 298   3 * 4,                        /* %ds */
 299   2 * 4,                        /* %es */
 300   0 * 4,                        /* %fs */
 301   1 * 4                         /* %gs */
 302 };
 303
 304 static struct trad_frame_cache *
 305 i386obsd_trapframe_cache (const frame_info_ptr &this_frame, void **this_cache)
 306 {
 307   struct gdbarch *gdbarch = get_frame_arch (this_frame);
 308   enum bfd_endian byte_order = gdbarch_byte_order (gdbarch);
 309   struct trad_frame_cache *cache;
 310   CORE_ADDR func, sp, addr;
 311   ULONGEST cs;
 312   const char *name;
 313   int i;
 314
 315   if (*this_cache)
 316     return (struct trad_frame_cache *) *this_cache;
 317
 318   cache = trad_frame_cache_zalloc (this_frame);
 319   *this_cache = cache;
 320
 321   func = get_frame_func (this_frame);
 322   sp = get_frame_register_unsigned (this_frame, I386_ESP_REGNUM);
 323
 324   find_pc_partial_function (func, &name, NULL, NULL);
 325   if (name && startswith (name, "Xintr"))
 326     addr = sp + 8;              /* It's an interrupt frame.  */
 327   else
 328     addr = sp;
 329
 330   for (i = 0; i < ARRAY_SIZE (i386obsd_tf_reg_offset); i++)
 331     if (i386obsd_tf_reg_offset[i] != -1)
 332       trad_frame_set_reg_addr (cache, i, addr + i386obsd_tf_reg_offset[i]);
 333
 334   /* Read %cs from trap frame.  */
 335   addr += i386obsd_tf_reg_offset[I386_CS_REGNUM];
 336   cs = read_memory_unsigned_integer (addr, 4, byte_order);
 337   if ((cs & I386_SEL_RPL) == I386_SEL_UPL)
 338     {
 339       /* Trap from user space; terminate backtrace.  */
 340       trad_frame_set_id (cache, outer_frame_id);
 341     }
 342   else
 343     {
 344       /* Construct the frame ID using the function start.  */
 345       trad_frame_set_id (cache, frame_id_build (sp + 8, func));
 346     }
 347
 348   return cache;
 349 }
 350
 351 static void
 352 i386obsd_trapframe_this_id (const frame_info_ptr &this_frame,
 353                             void **this_cache, struct frame_id *this_id)
 354 {
 355   struct trad_frame_cache *cache =
 356     i386obsd_trapframe_cache (this_frame, this_cache);
 357
 358   trad_frame_get_id (cache, this_id);
 359 }
 360
 361 static struct value *
 362 i386obsd_trapframe_prev_register (const frame_info_ptr &this_frame,
 363                                   void **this_cache, int regnum)
 364 {
 365   struct trad_frame_cache *cache =
 366     i386obsd_trapframe_cache (this_frame, this_cache);
 367
 368   return trad_frame_get_register (cache, this_frame, regnum);
 369 }
 370
 371 static int
 372 i386obsd_trapframe_sniffer (const struct frame_unwind *self,
 373                             const frame_info_ptr &this_frame,
 374                             void **this_prologue_cache)
 375 {
 376   ULONGEST cs;
 377   const char *name;
 378
 379   /* Check Current Privilege Level and bail out if we're not executing
 380      in kernel space.  */
 381   cs = get_frame_register_unsigned (this_frame, I386_CS_REGNUM);
 382   if ((cs & I386_SEL_RPL) == I386_SEL_UPL)
 383     return 0;
 384
 385   find_pc_partial_function (get_frame_pc (this_frame), &name, NULL, NULL);
 386   return (name && (strcmp (name, "calltrap") == 0
 387                    || strcmp (name, "syscall1") == 0
 388                    || startswith (name, "Xintr")
 389                    || startswith (name, "Xsoft")));
 390 }
 391
 392 static const struct frame_unwind i386obsd_trapframe_unwind = {
 393   "i386 openbsd trap",
 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   i386_gdbarch_tdep *tdep = gdbarch_tdep<i386_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 _initialize_i386obsd_tdep ();
 447 void
 448 _initialize_i386obsd_tdep ()
 449 {
 450   gdbarch_register_osabi (bfd_arch_i386, 0, GDB_OSABI_OPENBSD,
 451                           i386obsd_init_abi);
 452 }