gdb/inf-ptrace.c

   1 /* Low-level child interface to ptrace.
   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 "command.h"
  22 #include "inferior.h"
  23 #include "inflow.h"
  24 #include "terminal.h"
  25 #include "gdbcore.h"
  26 #include "regcache.h"
  27 #include "nat/gdb_ptrace.h"
  28 #include "gdbsupport/gdb_wait.h"
  29 #include <signal.h>
  30
  31 #include "inf-ptrace.h"
  32 #include "inf-child.h"
  33 #include "gdbthread.h"
  34 #include "nat/fork-inferior.h"
  35 #include "utils.h"
  36 #include "gdbarch.h"
  37
  38 \f
  39
  40 /* A unique_ptr helper to unpush a target.  */
  41
  42 struct target_unpusher
  43 {
  44   void operator() (struct target_ops *ops) const
  45   {
  46     unpush_target (ops);
  47   }
  48 };
  49
  50 /* A unique_ptr that unpushes a target on destruction.  */
  51
  52 typedef std::unique_ptr<struct target_ops, target_unpusher> target_unpush_up;
  53
  54 \f
  55
  56 inf_ptrace_target::~inf_ptrace_target ()
  57 {}
  58
  59 #ifdef PT_GET_PROCESS_STATE
  60
  61 /* Target hook for follow_fork.  On entry and at return inferior_ptid is
  62    the ptid of the followed inferior.  */
  63
  64 int
  65 inf_ptrace_target::follow_fork (int follow_child, int detach_fork)
  66 {
  67   if (!follow_child)
  68     {
  69       struct thread_info *tp = inferior_thread ();
  70       pid_t child_pid = tp->pending_follow.value.related_pid.pid ();
  71
  72       /* Breakpoints have already been detached from the child by
  73          infrun.c.  */
  74
  75       if (ptrace (PT_DETACH, child_pid, (PTRACE_TYPE_ARG3)1, 0) == -1)
  76         perror_with_name (("ptrace"));
  77     }
  78
  79   return 0;
  80 }
  81
  82 int
  83 inf_ptrace_target::insert_fork_catchpoint (int pid)
  84 {
  85   return 0;
  86 }
  87
  88 int
  89 inf_ptrace_target::remove_fork_catchpoint (int pid)
  90 {
  91   return 0;
  92 }
  93
  94 #endif /* PT_GET_PROCESS_STATE */
  95 \f
  96
  97 /* Prepare to be traced.  */
  98
  99 static void
 100 inf_ptrace_me (void)
 101 {
 102   /* "Trace me, Dr. Memory!"  */
 103   if (ptrace (PT_TRACE_ME, 0, (PTRACE_TYPE_ARG3) 0, 0) < 0)
 104     trace_start_error_with_name ("ptrace");
 105 }
 106
 107 /* Start a new inferior Unix child process.  EXEC_FILE is the file to
 108    run, ALLARGS is a string containing the arguments to the program.
 109    ENV is the environment vector to pass.  If FROM_TTY is non-zero, be
 110    chatty about it.  */
 111
 112 void
 113 inf_ptrace_target::create_inferior (const char *exec_file,
 114                                     const std::string &allargs,
 115                                     char **env, int from_tty)
 116 {
 117   pid_t pid;
 118   ptid_t ptid;
 119
 120   /* Do not change either targets above or the same target if already present.
 121      The reason is the target stack is shared across multiple inferiors.  */
 122   int ops_already_pushed = target_is_pushed (this);
 123
 124   target_unpush_up unpusher;
 125   if (! ops_already_pushed)
 126     {
 127       /* Clear possible core file with its process_stratum.  */
 128       push_target (this);
 129       unpusher.reset (this);
 130     }
 131
 132   pid = fork_inferior (exec_file, allargs, env, inf_ptrace_me, NULL,
 133                        NULL, NULL, NULL);
 134
 135   ptid = ptid_t (pid);
 136   /* We have something that executes now.  We'll be running through
 137      the shell at this point (if startup-with-shell is true), but the
 138      pid shouldn't change.  */
 139   add_thread_silent (this, ptid);
 140
 141   unpusher.release ();
 142
 143   gdb_startup_inferior (pid, START_INFERIOR_TRAPS_EXPECTED);
 144
 145   /* On some targets, there must be some explicit actions taken after
 146      the inferior has been started up.  */
 147   target_post_startup_inferior (ptid);
 148 }
 149
 150 #ifdef PT_GET_PROCESS_STATE
 151
 152 void
 153 inf_ptrace_target::post_startup_inferior (ptid_t pid)
 154 {
 155   ptrace_event_t pe;
 156
 157   /* Set the initial event mask.  */
 158   memset (&pe, 0, sizeof pe);
 159   pe.pe_set_event |= PTRACE_FORK;
 160   if (ptrace (PT_SET_EVENT_MASK, pid.pid (),
 161               (PTRACE_TYPE_ARG3)&pe, sizeof pe) == -1)
 162     perror_with_name (("ptrace"));
 163 }
 164
 165 #endif
 166
 167 /* Clean up a rotting corpse of an inferior after it died.  */
 168
 169 void
 170 inf_ptrace_target::mourn_inferior ()
 171 {
 172   int status;
 173
 174   /* Wait just one more time to collect the inferior's exit status.
 175      Do not check whether this succeeds though, since we may be
 176      dealing with a process that we attached to.  Such a process will
 177      only report its exit status to its original parent.  */
 178   waitpid (inferior_ptid.pid (), &status, 0);
 179
 180   inf_child_target::mourn_inferior ();
 181 }
 182
 183 /* Attach to the process specified by ARGS.  If FROM_TTY is non-zero,
 184    be chatty about it.  */
 185
 186 void
 187 inf_ptrace_target::attach (const char *args, int from_tty)
 188 {
 189   pid_t pid;
 190   struct inferior *inf;
 191
 192   /* Do not change either targets above or the same target if already present.
 193      The reason is the target stack is shared across multiple inferiors.  */
 194   int ops_already_pushed = target_is_pushed (this);
 195
 196   pid = parse_pid_to_attach (args);
 197
 198   if (pid == getpid ())         /* Trying to masturbate?  */
 199     error (_("I refuse to debug myself!"));
 200
 201   target_unpush_up unpusher;
 202   if (! ops_already_pushed)
 203     {
 204       /* target_pid_to_str already uses the target.  Also clear possible core
 205          file with its process_stratum.  */
 206       push_target (this);
 207       unpusher.reset (this);
 208     }
 209
 210   if (from_tty)
 211     {
 212       const char *exec_file = get_exec_file (0);
 213
 214       if (exec_file)
 215         printf_unfiltered (_("Attaching to program: %s, %s\n"), exec_file,
 216                            target_pid_to_str (ptid_t (pid)).c_str ());
 217       else
 218         printf_unfiltered (_("Attaching to %s\n"),
 219                            target_pid_to_str (ptid_t (pid)).c_str ());
 220     }
 221
 222 #ifdef PT_ATTACH
 223   errno = 0;
 224   ptrace (PT_ATTACH, pid, (PTRACE_TYPE_ARG3)0, 0);
 225   if (errno != 0)
 226     perror_with_name (("ptrace"));
 227 #else
 228   error (_("This system does not support attaching to a process"));
 229 #endif
 230
 231   inf = current_inferior ();
 232   inferior_appeared (inf, pid);
 233   inf->attach_flag = 1;
 234   inferior_ptid = ptid_t (pid);
 235
 236   /* Always add a main thread.  If some target extends the ptrace
 237      target, it should decorate the ptid later with more info.  */
 238   thread_info *thr = add_thread_silent (this, inferior_ptid);
 239   /* Don't consider the thread stopped until we've processed its
 240      initial SIGSTOP stop.  */
 241   set_executing (this, thr->ptid, true);
 242
 243   unpusher.release ();
 244 }
 245
 246 #ifdef PT_GET_PROCESS_STATE
 247
 248 void
 249 inf_ptrace_target::post_attach (int pid)
 250 {
 251   ptrace_event_t pe;
 252
 253   /* Set the initial event mask.  */
 254   memset (&pe, 0, sizeof pe);
 255   pe.pe_set_event |= PTRACE_FORK;
 256   if (ptrace (PT_SET_EVENT_MASK, pid,
 257               (PTRACE_TYPE_ARG3)&pe, sizeof pe) == -1)
 258     perror_with_name (("ptrace"));
 259 }
 260
 261 #endif
 262
 263 /* Detach from the inferior.  If FROM_TTY is non-zero, be chatty about it.  */
 264
 265 void
 266 inf_ptrace_target::detach (inferior *inf, int from_tty)
 267 {
 268   pid_t pid = inferior_ptid.pid ();
 269
 270   target_announce_detach (from_tty);
 271
 272 #ifdef PT_DETACH
 273   /* We'd better not have left any breakpoints in the program or it'll
 274      die when it hits one.  Also note that this may only work if we
 275      previously attached to the inferior.  It *might* work if we
 276      started the process ourselves.  */
 277   errno = 0;
 278   ptrace (PT_DETACH, pid, (PTRACE_TYPE_ARG3)1, 0);
 279   if (errno != 0)
 280     perror_with_name (("ptrace"));
 281 #else
 282   error (_("This system does not support detaching from a process"));
 283 #endif
 284
 285   detach_success (inf);
 286 }
 287
 288 /* See inf-ptrace.h.  */
 289
 290 void
 291 inf_ptrace_target::detach_success (inferior *inf)
 292 {
 293   inferior_ptid = null_ptid;
 294   detach_inferior (inf);
 295
 296   maybe_unpush_target ();
 297 }
 298
 299 /* Kill the inferior.  */
 300
 301 void
 302 inf_ptrace_target::kill ()
 303 {
 304   pid_t pid = inferior_ptid.pid ();
 305   int status;
 306
 307   if (pid == 0)
 308     return;
 309
 310   ptrace (PT_KILL, pid, (PTRACE_TYPE_ARG3)0, 0);
 311   waitpid (pid, &status, 0);
 312
 313   target_mourn_inferior (inferior_ptid);
 314 }
 315
 316 /* Return which PID to pass to ptrace in order to observe/control the
 317    tracee identified by PTID.  */
 318
 319 pid_t
 320 get_ptrace_pid (ptid_t ptid)
 321 {
 322   pid_t pid;
 323
 324   /* If we have an LWPID to work with, use it.  Otherwise, we're
 325      dealing with a non-threaded program/target.  */
 326   pid = ptid.lwp ();
 327   if (pid == 0)
 328     pid = ptid.pid ();
 329   return pid;
 330 }
 331
 332 /* Resume execution of thread PTID, or all threads if PTID is -1.  If
 333    STEP is nonzero, single-step it.  If SIGNAL is nonzero, give it
 334    that signal.  */
 335
 336 void
 337 inf_ptrace_target::resume (ptid_t ptid, int step, enum gdb_signal signal)
 338 {
 339   pid_t pid;
 340   int request;
 341
 342   if (minus_one_ptid == ptid)
 343     /* Resume all threads.  Traditionally ptrace() only supports
 344        single-threaded processes, so simply resume the inferior.  */
 345     pid = inferior_ptid.pid ();
 346   else
 347     pid = get_ptrace_pid (ptid);
 348
 349   if (catch_syscall_enabled () > 0)
 350     request = PT_SYSCALL;
 351   else
 352     request = PT_CONTINUE;
 353
 354   if (step)
 355     {
 356       /* If this system does not support PT_STEP, a higher level
 357          function will have called single_step() to transmute the step
 358          request into a continue request (by setting breakpoints on
 359          all possible successor instructions), so we don't have to
 360          worry about that here.  */
 361       request = PT_STEP;
 362     }
 363
 364   /* An address of (PTRACE_TYPE_ARG3)1 tells ptrace to continue from
 365      where it was.  If GDB wanted it to start some other way, we have
 366      already written a new program counter value to the child.  */
 367   errno = 0;
 368   ptrace (request, pid, (PTRACE_TYPE_ARG3)1, gdb_signal_to_host (signal));
 369   if (errno != 0)
 370     perror_with_name (("ptrace"));
 371 }
 372
 373 /* Wait for the child specified by PTID to do something.  Return the
 374    process ID of the child, or MINUS_ONE_PTID in case of error; store
 375    the status in *OURSTATUS.  */
 376
 377 ptid_t
 378 inf_ptrace_target::wait (ptid_t ptid, struct target_waitstatus *ourstatus,
 379                          int options)
 380 {
 381   pid_t pid;
 382   int status, save_errno;
 383
 384   do
 385     {
 386       set_sigint_trap ();
 387
 388       do
 389         {
 390           pid = waitpid (ptid.pid (), &status, 0);
 391           save_errno = errno;
 392         }
 393       while (pid == -1 && errno == EINTR);
 394
 395       clear_sigint_trap ();
 396
 397       if (pid == -1)
 398         {
 399           fprintf_unfiltered (gdb_stderr,
 400                               _("Child process unexpectedly missing: %s.\n"),
 401                               safe_strerror (save_errno));
 402
 403           /* Claim it exited with unknown signal.  */
 404           ourstatus->kind = TARGET_WAITKIND_SIGNALLED;
 405           ourstatus->value.sig = GDB_SIGNAL_UNKNOWN;
 406           return inferior_ptid;
 407         }
 408
 409       /* Ignore terminated detached child processes.  */
 410       if (!WIFSTOPPED (status) && pid != inferior_ptid.pid ())
 411         pid = -1;
 412     }
 413   while (pid == -1);
 414
 415 #ifdef PT_GET_PROCESS_STATE
 416   if (WIFSTOPPED (status))
 417     {
 418       ptrace_state_t pe;
 419       pid_t fpid;
 420
 421       if (ptrace (PT_GET_PROCESS_STATE, pid,
 422                   (PTRACE_TYPE_ARG3)&pe, sizeof pe) == -1)
 423         perror_with_name (("ptrace"));
 424
 425       switch (pe.pe_report_event)
 426         {
 427         case PTRACE_FORK:
 428           ourstatus->kind = TARGET_WAITKIND_FORKED;
 429           ourstatus->value.related_pid = ptid_t (pe.pe_other_pid);
 430
 431           /* Make sure the other end of the fork is stopped too.  */
 432           fpid = waitpid (pe.pe_other_pid, &status, 0);
 433           if (fpid == -1)
 434             perror_with_name (("waitpid"));
 435
 436           if (ptrace (PT_GET_PROCESS_STATE, fpid,
 437                       (PTRACE_TYPE_ARG3)&pe, sizeof pe) == -1)
 438             perror_with_name (("ptrace"));
 439
 440           gdb_assert (pe.pe_report_event == PTRACE_FORK);
 441           gdb_assert (pe.pe_other_pid == pid);
 442           if (fpid == inferior_ptid.pid ())
 443             {
 444               ourstatus->value.related_pid = ptid_t (pe.pe_other_pid);
 445               return ptid_t (fpid);
 446             }
 447
 448           return ptid_t (pid);
 449         }
 450     }
 451 #endif
 452
 453   store_waitstatus (ourstatus, status);
 454   return ptid_t (pid);
 455 }
 456
 457 /* Transfer data via ptrace into process PID's memory from WRITEBUF, or
 458    from process PID's memory into READBUF.  Start at target address ADDR
 459    and transfer up to LEN bytes.  Exactly one of READBUF and WRITEBUF must
 460    be non-null.  Return the number of transferred bytes.  */
 461
 462 static ULONGEST
 463 inf_ptrace_peek_poke (pid_t pid, gdb_byte *readbuf,
 464                       const gdb_byte *writebuf,
 465                       ULONGEST addr, ULONGEST len)
 466 {
 467   ULONGEST n;
 468   unsigned int chunk;
 469
 470   /* We transfer aligned words.  Thus align ADDR down to a word
 471      boundary and determine how many bytes to skip at the
 472      beginning.  */
 473   ULONGEST skip = addr & (sizeof (PTRACE_TYPE_RET) - 1);
 474   addr -= skip;
 475
 476   for (n = 0;
 477        n < len;
 478        n += chunk, addr += sizeof (PTRACE_TYPE_RET), skip = 0)
 479     {
 480       /* Restrict to a chunk that fits in the current word.  */
 481       chunk = std::min (sizeof (PTRACE_TYPE_RET) - skip, len - n);
 482
 483       /* Use a union for type punning.  */
 484       union
 485       {
 486         PTRACE_TYPE_RET word;
 487         gdb_byte byte[sizeof (PTRACE_TYPE_RET)];
 488       } buf;
 489
 490       /* Read the word, also when doing a partial word write.  */
 491       if (readbuf != NULL || chunk < sizeof (PTRACE_TYPE_RET))
 492         {
 493           errno = 0;
 494           buf.word = ptrace (PT_READ_I, pid,
 495                              (PTRACE_TYPE_ARG3)(uintptr_t) addr, 0);
 496           if (errno != 0)
 497             break;
 498           if (readbuf != NULL)
 499             memcpy (readbuf + n, buf.byte + skip, chunk);
 500         }
 501       if (writebuf != NULL)
 502         {
 503           memcpy (buf.byte + skip, writebuf + n, chunk);
 504           errno = 0;
 505           ptrace (PT_WRITE_D, pid, (PTRACE_TYPE_ARG3)(uintptr_t) addr,
 506                   buf.word);
 507           if (errno != 0)
 508             {
 509               /* Using the appropriate one (I or D) is necessary for
 510                  Gould NP1, at least.  */
 511               errno = 0;
 512               ptrace (PT_WRITE_I, pid, (PTRACE_TYPE_ARG3)(uintptr_t) addr,
 513                       buf.word);
 514               if (errno != 0)
 515                 break;
 516             }
 517         }
 518     }
 519
 520   return n;
 521 }
 522
 523 /* Implement the to_xfer_partial target_ops method.  */
 524
 525 enum target_xfer_status
 526 inf_ptrace_target::xfer_partial (enum target_object object,
 527                                  const char *annex, gdb_byte *readbuf,
 528                                  const gdb_byte *writebuf,
 529                                  ULONGEST offset, ULONGEST len, ULONGEST *xfered_len)
 530 {
 531   pid_t pid = get_ptrace_pid (inferior_ptid);
 532
 533   switch (object)
 534     {
 535     case TARGET_OBJECT_MEMORY:
 536 #ifdef PT_IO
 537       /* OpenBSD 3.1, NetBSD 1.6 and FreeBSD 5.0 have a new PT_IO
 538          request that promises to be much more efficient in reading
 539          and writing data in the traced process's address space.  */
 540       {
 541         struct ptrace_io_desc piod;
 542
 543         /* NOTE: We assume that there are no distinct address spaces
 544            for instruction and data.  However, on OpenBSD 3.9 and
 545            later, PIOD_WRITE_D doesn't allow changing memory that's
 546            mapped read-only.  Since most code segments will be
 547            read-only, using PIOD_WRITE_D will prevent us from
 548            inserting breakpoints, so we use PIOD_WRITE_I instead.  */
 549         piod.piod_op = writebuf ? PIOD_WRITE_I : PIOD_READ_D;
 550         piod.piod_addr = writebuf ? (void *) writebuf : readbuf;
 551         piod.piod_offs = (void *) (long) offset;
 552         piod.piod_len = len;
 553
 554         errno = 0;
 555         if (ptrace (PT_IO, pid, (caddr_t)&piod, 0) == 0)
 556           {
 557             /* Return the actual number of bytes read or written.  */
 558             *xfered_len = piod.piod_len;
 559             return (piod.piod_len == 0) ? TARGET_XFER_EOF : TARGET_XFER_OK;
 560           }
 561         /* If the PT_IO request is somehow not supported, fallback on
 562            using PT_WRITE_D/PT_READ_D.  Otherwise we will return zero
 563            to indicate failure.  */
 564         if (errno != EINVAL)
 565           return TARGET_XFER_EOF;
 566       }
 567 #endif
 568       *xfered_len = inf_ptrace_peek_poke (pid, readbuf, writebuf,
 569                                           offset, len);
 570       return *xfered_len != 0 ? TARGET_XFER_OK : TARGET_XFER_EOF;
 571
 572     case TARGET_OBJECT_UNWIND_TABLE:
 573       return TARGET_XFER_E_IO;
 574
 575     case TARGET_OBJECT_AUXV:
 576 #if defined (PT_IO) && defined (PIOD_READ_AUXV)
 577       /* OpenBSD 4.5 has a new PIOD_READ_AUXV operation for the PT_IO
 578          request that allows us to read the auxilliary vector.  Other
 579          BSD's may follow if they feel the need to support PIE.  */
 580       {
 581         struct ptrace_io_desc piod;
 582
 583         if (writebuf)
 584           return TARGET_XFER_E_IO;
 585         piod.piod_op = PIOD_READ_AUXV;
 586         piod.piod_addr = readbuf;
 587         piod.piod_offs = (void *) (long) offset;
 588         piod.piod_len = len;
 589
 590         errno = 0;
 591         if (ptrace (PT_IO, pid, (caddr_t)&piod, 0) == 0)
 592           {
 593             /* Return the actual number of bytes read or written.  */
 594             *xfered_len = piod.piod_len;
 595             return (piod.piod_len == 0) ? TARGET_XFER_EOF : TARGET_XFER_OK;
 596           }
 597       }
 598 #endif
 599       return TARGET_XFER_E_IO;
 600
 601     case TARGET_OBJECT_WCOOKIE:
 602       return TARGET_XFER_E_IO;
 603
 604     default:
 605       return TARGET_XFER_E_IO;
 606     }
 607 }
 608
 609 /* Return non-zero if the thread specified by PTID is alive.  */
 610
 611 bool
 612 inf_ptrace_target::thread_alive (ptid_t ptid)
 613 {
 614   /* ??? Is kill the right way to do this?  */
 615   return (::kill (ptid.pid (), 0) != -1);
 616 }
 617
 618 /* Print status information about what we're accessing.  */
 619
 620 void
 621 inf_ptrace_target::files_info ()
 622 {
 623   struct inferior *inf = current_inferior ();
 624
 625   printf_filtered (_("\tUsing the running image of %s %s.\n"),
 626                    inf->attach_flag ? "attached" : "child",
 627                    target_pid_to_str (inferior_ptid).c_str ());
 628 }
 629
 630 std::string
 631 inf_ptrace_target::pid_to_str (ptid_t ptid)
 632 {
 633   return normal_pid_to_str (ptid);
 634 }
 635
 636 #if defined (PT_IO) && defined (PIOD_READ_AUXV)
 637
 638 /* Read one auxv entry from *READPTR, not reading locations >= ENDPTR.
 639    Return 0 if *READPTR is already at the end of the buffer.
 640    Return -1 if there is insufficient buffer for a whole entry.
 641    Return 1 if an entry was read into *TYPEP and *VALP.  */
 642
 643 int
 644 inf_ptrace_target::auxv_parse (gdb_byte **readptr, gdb_byte *endptr,
 645                                CORE_ADDR *typep, CORE_ADDR *valp)
 646 {
 647   struct type *int_type = builtin_type (target_gdbarch ())->builtin_int;
 648   struct type *ptr_type = builtin_type (target_gdbarch ())->builtin_data_ptr;
 649   const int sizeof_auxv_type = TYPE_LENGTH (int_type);
 650   const int sizeof_auxv_val = TYPE_LENGTH (ptr_type);
 651   enum bfd_endian byte_order = gdbarch_byte_order (target_gdbarch ());
 652   gdb_byte *ptr = *readptr;
 653
 654   if (endptr == ptr)
 655     return 0;
 656
 657   if (endptr - ptr < 2 * sizeof_auxv_val)
 658     return -1;
 659
 660   *typep = extract_unsigned_integer (ptr, sizeof_auxv_type, byte_order);
 661   ptr += sizeof_auxv_val;       /* Alignment.  */
 662   *valp = extract_unsigned_integer (ptr, sizeof_auxv_val, byte_order);
 663   ptr += sizeof_auxv_val;
 664
 665   *readptr = ptr;
 666   return 1;
 667 }
 668
 669 #endif
 670 \f