gdb/ravenscar-thread.c

   1 /* Ada Ravenscar thread support.
   2
   3    Copyright (C) 2004-2020 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 "gdbcore.h"
  22 #include "gdbthread.h"
  23 #include "ada-lang.h"
  24 #include "target.h"
  25 #include "inferior.h"
  26 #include "command.h"
  27 #include "ravenscar-thread.h"
  28 #include "observable.h"
  29 #include "gdbcmd.h"
  30 #include "top.h"
  31 #include "regcache.h"
  32 #include "objfiles.h"
  33
  34 /* This module provides support for "Ravenscar" tasks (Ada) when
  35    debugging on bare-metal targets.
  36
  37    The typical situation is when debugging a bare-metal target over
  38    the remote protocol. In that situation, the system does not know
  39    about high-level concepts such as threads, only about some code
  40    running on one or more CPUs. And since the remote protocol does not
  41    provide any handling for CPUs, the de facto standard for handling
  42    them is to have one thread per CPU, where the thread's ptid has
  43    its lwp field set to the CPU number (eg: 1 for the first CPU,
  44    2 for the second one, etc).  This module will make that assumption.
  45
  46    This module then creates and maintains the list of threads based
  47    on the list of Ada tasks, with one thread per Ada task. The convention
  48    is that threads corresponding to the CPUs (see assumption above)
  49    have a ptid_t of the form (PID, LWP, 0), while threads corresponding
  50    to our Ada tasks have a ptid_t of the form (PID, 0, TID) where TID
  51    is the Ada task's ID as extracted from Ada runtime information.
  52
  53    Switching to a given Ada task (or its underlying thread) is performed
  54    by fetching the registers of that task from the memory area where
  55    the registers were saved.  For any of the other operations, the
  56    operation is performed by first finding the CPU on which the task
  57    is running, switching to its corresponding ptid, and then performing
  58    the operation on that ptid using the target beneath us.  */
  59
  60 /* If true, ravenscar task support is enabled.  */
  61 static bool ravenscar_task_support = true;
  62
  63 static const char running_thread_name[] = "__gnat_running_thread_table";
  64
  65 static const char known_tasks_name[] = "system__tasking__debug__known_tasks";
  66 static const char first_task_name[] = "system__tasking__debug__first_task";
  67
  68 static const char ravenscar_runtime_initializer[]
  69   = "system__bb__threads__initialize";
  70
  71 static const target_info ravenscar_target_info = {
  72   "ravenscar",
  73   N_("Ravenscar tasks."),
  74   N_("Ravenscar tasks support.")
  75 };
  76
  77 struct ravenscar_thread_target final : public target_ops
  78 {
  79   ravenscar_thread_target ()
  80     : m_base_ptid (inferior_ptid)
  81   {
  82     thread_info *thr = add_active_thread ();
  83     if (thr != nullptr)
  84       switch_to_thread (thr);
  85   }
  86
  87   const target_info &info () const override
  88   { return ravenscar_target_info; }
  89
  90   strata stratum () const override { return thread_stratum; }
  91
  92   ptid_t wait (ptid_t, struct target_waitstatus *, int) override;
  93   void resume (ptid_t, int, enum gdb_signal) override;
  94
  95   void fetch_registers (struct regcache *, int) override;
  96   void store_registers (struct regcache *, int) override;
  97
  98   void prepare_to_store (struct regcache *) override;
  99
 100   bool stopped_by_sw_breakpoint () override;
 101
 102   bool stopped_by_hw_breakpoint () override;
 103
 104   bool stopped_by_watchpoint () override;
 105
 106   bool stopped_data_address (CORE_ADDR *) override;
 107
 108   bool thread_alive (ptid_t ptid) override;
 109
 110   int core_of_thread (ptid_t ptid) override;
 111
 112   void update_thread_list () override;
 113
 114   const char *extra_thread_info (struct thread_info *) override;
 115
 116   std::string pid_to_str (ptid_t) override;
 117
 118   ptid_t get_ada_task_ptid (long lwp, long thread) override;
 119
 120   void mourn_inferior () override;
 121
 122   void close () override
 123   {
 124     delete this;
 125   }
 126
 127 private:
 128
 129   /* PTID of the last thread that received an event.
 130      This can be useful to determine the associated task that received
 131      the event, to make it the current task.  */
 132   ptid_t m_base_ptid;
 133
 134   thread_info *add_active_thread ();
 135   ptid_t active_task (int cpu);
 136   bool task_is_currently_active (ptid_t ptid);
 137   bool runtime_initialized ();
 138 };
 139
 140 /* Return true iff PTID corresponds to a ravenscar task.  */
 141
 142 static bool
 143 is_ravenscar_task (ptid_t ptid)
 144 {
 145   /* By construction, ravenscar tasks have their LWP set to zero.
 146      Also make sure that the TID is nonzero, as some remotes, when
 147      asked for the list of threads, will return the first thread
 148      as having its TID set to zero.  For instance, TSIM version
 149      2.0.48 for LEON3 sends 'm0' as a reply to the 'qfThreadInfo'
 150      query, which the remote protocol layer then treats as a thread
 151      whose TID is 0.  This is obviously not a ravenscar task.  */
 152   return ptid.lwp () == 0 && ptid.tid () != 0;
 153 }
 154
 155 /* Given PTID, which can be either a ravenscar task or a CPU thread,
 156    return which CPU that ptid is running on.
 157
 158    This assume that PTID is a valid ptid_t.  Otherwise, a gdb_assert
 159    will be triggered.  */
 160
 161 static int
 162 ravenscar_get_thread_base_cpu (ptid_t ptid)
 163 {
 164   int base_cpu;
 165
 166   if (is_ravenscar_task (ptid))
 167     {
 168       struct ada_task_info *task_info = ada_get_task_info_from_ptid (ptid);
 169
 170       gdb_assert (task_info != NULL);
 171       base_cpu = task_info->base_cpu;
 172     }
 173   else
 174     {
 175       /* We assume that the LWP of the PTID is equal to the CPU number.  */
 176       base_cpu = ptid.lwp ();
 177     }
 178
 179   return base_cpu;
 180 }
 181
 182 /* Given a ravenscar task (identified by its ptid_t PTID), return true
 183    if this task is the currently active task on the cpu that task is
 184    running on.
 185
 186    In other words, this function determine which CPU this task is
 187    currently running on, and then return nonzero if the CPU in question
 188    is executing the code for that task.  If that's the case, then
 189    that task's registers are in the CPU bank.  Otherwise, the task
 190    is currently suspended, and its registers have been saved in memory.  */
 191
 192 bool
 193 ravenscar_thread_target::task_is_currently_active (ptid_t ptid)
 194 {
 195   ptid_t active_task_ptid
 196     = active_task (ravenscar_get_thread_base_cpu (ptid));
 197
 198   return ptid == active_task_ptid;
 199 }
 200
 201 /* Return the CPU thread (as a ptid_t) on which the given ravenscar
 202    task is running.
 203
 204    This is the thread that corresponds to the CPU on which the task
 205    is running.  */
 206
 207 static ptid_t
 208 get_base_thread_from_ravenscar_task (ptid_t ptid)
 209 {
 210   int base_cpu;
 211
 212   if (!is_ravenscar_task (ptid))
 213     return ptid;
 214
 215   base_cpu = ravenscar_get_thread_base_cpu (ptid);
 216   return ptid_t (ptid.pid (), base_cpu, 0);
 217 }
 218
 219 /* Fetch the ravenscar running thread from target memory, make sure
 220    there's a corresponding thread in the thread list, and return it.
 221    If the runtime is not initialized, return NULL.  */
 222
 223 thread_info *
 224 ravenscar_thread_target::add_active_thread ()
 225 {
 226   process_stratum_target *proc_target
 227     = as_process_stratum_target (this->beneath ());
 228
 229   int base_cpu;
 230
 231   gdb_assert (!is_ravenscar_task (m_base_ptid));
 232   base_cpu = ravenscar_get_thread_base_cpu (m_base_ptid);
 233
 234   if (!runtime_initialized ())
 235     return nullptr;
 236
 237   /* Make sure we set m_base_ptid before calling active_task
 238      as the latter relies on it.  */
 239   ptid_t active_ptid = active_task (base_cpu);
 240   gdb_assert (active_ptid != null_ptid);
 241
 242   /* The running thread may not have been added to
 243      system.tasking.debug's list yet; so ravenscar_update_thread_list
 244      may not always add it to the thread list.  Add it here.  */
 245   thread_info *active_thr = find_thread_ptid (proc_target, active_ptid);
 246   if (active_thr == nullptr)
 247     active_thr = add_thread (proc_target, active_ptid);
 248   return active_thr;
 249 }
 250
 251 /* The Ravenscar Runtime exports a symbol which contains the ID of
 252    the thread that is currently running.  Try to locate that symbol
 253    and return its associated minimal symbol.
 254    Return NULL if not found.  */
 255
 256 static struct bound_minimal_symbol
 257 get_running_thread_msymbol ()
 258 {
 259   struct bound_minimal_symbol msym;
 260
 261   msym = lookup_minimal_symbol (running_thread_name, NULL, NULL);
 262   if (!msym.minsym)
 263     /* Older versions of the GNAT runtime were using a different
 264        (less ideal) name for the symbol where the active thread ID
 265        is stored.  If we couldn't find the symbol using the latest
 266        name, then try the old one.  */
 267     msym = lookup_minimal_symbol ("running_thread", NULL, NULL);
 268
 269   return msym;
 270 }
 271
 272 /* Return True if the Ada Ravenscar run-time can be found in the
 273    application.  */
 274
 275 static bool
 276 has_ravenscar_runtime ()
 277 {
 278   struct bound_minimal_symbol msym_ravenscar_runtime_initializer
 279     = lookup_minimal_symbol (ravenscar_runtime_initializer, NULL, NULL);
 280   struct bound_minimal_symbol msym_known_tasks
 281     = lookup_minimal_symbol (known_tasks_name, NULL, NULL);
 282   struct bound_minimal_symbol msym_first_task
 283     = lookup_minimal_symbol (first_task_name, NULL, NULL);
 284   struct bound_minimal_symbol msym_running_thread
 285     = get_running_thread_msymbol ();
 286
 287   return (msym_ravenscar_runtime_initializer.minsym
 288           && (msym_known_tasks.minsym || msym_first_task.minsym)
 289           && msym_running_thread.minsym);
 290 }
 291
 292 /* Return True if the Ada Ravenscar run-time can be found in the
 293    application, and if it has been initialized on target.  */
 294
 295 bool
 296 ravenscar_thread_target::runtime_initialized ()
 297 {
 298   return active_task (1) != null_ptid;
 299 }
 300
 301 /* Return the ID of the thread that is currently running.
 302    Return 0 if the ID could not be determined.  */
 303
 304 static CORE_ADDR
 305 get_running_thread_id (int cpu)
 306 {
 307   struct bound_minimal_symbol object_msym = get_running_thread_msymbol ();
 308   int object_size;
 309   int buf_size;
 310   gdb_byte *buf;
 311   CORE_ADDR object_addr;
 312   struct type *builtin_type_void_data_ptr
 313     = builtin_type (target_gdbarch ())->builtin_data_ptr;
 314
 315   if (!object_msym.minsym)
 316     return 0;
 317
 318   object_size = TYPE_LENGTH (builtin_type_void_data_ptr);
 319   object_addr = (BMSYMBOL_VALUE_ADDRESS (object_msym)
 320                  + (cpu - 1) * object_size);
 321   buf_size = object_size;
 322   buf = (gdb_byte *) alloca (buf_size);
 323   read_memory (object_addr, buf, buf_size);
 324   return extract_typed_address (buf, builtin_type_void_data_ptr);
 325 }
 326
 327 void
 328 ravenscar_thread_target::resume (ptid_t ptid, int step,
 329                                  enum gdb_signal siggnal)
 330 {
 331   /* If we see a wildcard resume, we simply pass that on.  Otherwise,
 332      arrange to resume the base ptid.  */
 333   inferior_ptid = m_base_ptid;
 334   if (ptid != minus_one_ptid)
 335     ptid = m_base_ptid;
 336   beneath ()->resume (ptid, step, siggnal);
 337 }
 338
 339 ptid_t
 340 ravenscar_thread_target::wait (ptid_t ptid,
 341                                struct target_waitstatus *status,
 342                                int options)
 343 {
 344   process_stratum_target *beneath
 345     = as_process_stratum_target (this->beneath ());
 346   ptid_t event_ptid;
 347
 348   if (ptid != minus_one_ptid)
 349     ptid = m_base_ptid;
 350   event_ptid = beneath->wait (ptid, status, 0);
 351   /* Find any new threads that might have been created, and return the
 352      active thread.
 353
 354      Only do it if the program is still alive, though.  Otherwise,
 355      this causes problems when debugging through the remote protocol,
 356      because we might try switching threads (and thus sending packets)
 357      after the remote has disconnected.  */
 358   if (status->kind != TARGET_WAITKIND_EXITED
 359       && status->kind != TARGET_WAITKIND_SIGNALLED)
 360     {
 361       m_base_ptid = event_ptid;
 362       this->update_thread_list ();
 363       return this->add_active_thread ()->ptid;
 364     }
 365   return m_base_ptid;
 366 }
 367
 368 /* Add the thread associated to the given TASK to the thread list
 369    (if the thread has already been added, this is a no-op).  */
 370
 371 static void
 372 ravenscar_add_thread (struct ada_task_info *task)
 373 {
 374   if (find_thread_ptid (current_inferior (), task->ptid) == NULL)
 375     add_thread (current_inferior ()->process_target (), task->ptid);
 376 }
 377
 378 void
 379 ravenscar_thread_target::update_thread_list ()
 380 {
 381   /* Do not clear the thread list before adding the Ada task, to keep
 382      the thread that the process stratum has included into it
 383      (m_base_ptid) and the running thread, that may not have been included
 384      to system.tasking.debug's list yet.  */
 385
 386   iterate_over_live_ada_tasks (ravenscar_add_thread);
 387 }
 388
 389 ptid_t
 390 ravenscar_thread_target::active_task (int cpu)
 391 {
 392   CORE_ADDR tid = get_running_thread_id (cpu);
 393
 394   if (tid == 0)
 395     return null_ptid;
 396   else
 397     return ptid_t (m_base_ptid.pid (), 0, tid);
 398 }
 399
 400 const char *
 401 ravenscar_thread_target::extra_thread_info (thread_info *tp)
 402 {
 403   return "Ravenscar task";
 404 }
 405
 406 bool
 407 ravenscar_thread_target::thread_alive (ptid_t ptid)
 408 {
 409   /* Ravenscar tasks are non-terminating.  */
 410   return true;
 411 }
 412
 413 std::string
 414 ravenscar_thread_target::pid_to_str (ptid_t ptid)
 415 {
 416   return string_printf ("Thread %#x", (int) ptid.tid ());
 417 }
 418
 419 void
 420 ravenscar_thread_target::fetch_registers (struct regcache *regcache, int regnum)
 421 {
 422   ptid_t ptid = regcache->ptid ();
 423
 424   if (runtime_initialized ()
 425       && is_ravenscar_task (ptid)
 426       && !task_is_currently_active (ptid))
 427     {
 428       struct gdbarch *gdbarch = regcache->arch ();
 429       struct ravenscar_arch_ops *arch_ops
 430         = gdbarch_ravenscar_ops (gdbarch);
 431
 432       arch_ops->fetch_registers (regcache, regnum);
 433     }
 434   else
 435     beneath ()->fetch_registers (regcache, regnum);
 436 }
 437
 438 void
 439 ravenscar_thread_target::store_registers (struct regcache *regcache,
 440                                           int regnum)
 441 {
 442   ptid_t ptid = regcache->ptid ();
 443
 444   if (runtime_initialized ()
 445       && is_ravenscar_task (ptid)
 446       && !task_is_currently_active (ptid))
 447     {
 448       struct gdbarch *gdbarch = regcache->arch ();
 449       struct ravenscar_arch_ops *arch_ops
 450         = gdbarch_ravenscar_ops (gdbarch);
 451
 452       arch_ops->store_registers (regcache, regnum);
 453     }
 454   else
 455     beneath ()->store_registers (regcache, regnum);
 456 }
 457
 458 void
 459 ravenscar_thread_target::prepare_to_store (struct regcache *regcache)
 460 {
 461   ptid_t ptid = regcache->ptid ();
 462
 463   if (runtime_initialized ()
 464       && is_ravenscar_task (ptid)
 465       && !task_is_currently_active (ptid))
 466     {
 467       /* Nothing.  */
 468     }
 469   else
 470     beneath ()->prepare_to_store (regcache);
 471 }
 472
 473 /* Implement the to_stopped_by_sw_breakpoint target_ops "method".  */
 474
 475 bool
 476 ravenscar_thread_target::stopped_by_sw_breakpoint ()
 477 {
 478   scoped_restore save_ptid = make_scoped_restore (&inferior_ptid);
 479   inferior_ptid = get_base_thread_from_ravenscar_task (inferior_ptid);
 480   return beneath ()->stopped_by_sw_breakpoint ();
 481 }
 482
 483 /* Implement the to_stopped_by_hw_breakpoint target_ops "method".  */
 484
 485 bool
 486 ravenscar_thread_target::stopped_by_hw_breakpoint ()
 487 {
 488   scoped_restore save_ptid = make_scoped_restore (&inferior_ptid);
 489   inferior_ptid = get_base_thread_from_ravenscar_task (inferior_ptid);
 490   return beneath ()->stopped_by_hw_breakpoint ();
 491 }
 492
 493 /* Implement the to_stopped_by_watchpoint target_ops "method".  */
 494
 495 bool
 496 ravenscar_thread_target::stopped_by_watchpoint ()
 497 {
 498   scoped_restore save_ptid = make_scoped_restore (&inferior_ptid);
 499   inferior_ptid = get_base_thread_from_ravenscar_task (inferior_ptid);
 500   return beneath ()->stopped_by_watchpoint ();
 501 }
 502
 503 /* Implement the to_stopped_data_address target_ops "method".  */
 504
 505 bool
 506 ravenscar_thread_target::stopped_data_address (CORE_ADDR *addr_p)
 507 {
 508   scoped_restore save_ptid = make_scoped_restore (&inferior_ptid);
 509   inferior_ptid = get_base_thread_from_ravenscar_task (inferior_ptid);
 510   return beneath ()->stopped_data_address (addr_p);
 511 }
 512
 513 void
 514 ravenscar_thread_target::mourn_inferior ()
 515 {
 516   m_base_ptid = null_ptid;
 517   target_ops *beneath = this->beneath ();
 518   unpush_target (this);
 519   beneath->mourn_inferior ();
 520 }
 521
 522 /* Implement the to_core_of_thread target_ops "method".  */
 523
 524 int
 525 ravenscar_thread_target::core_of_thread (ptid_t ptid)
 526 {
 527   scoped_restore save_ptid = make_scoped_restore (&inferior_ptid);
 528   inferior_ptid = get_base_thread_from_ravenscar_task (inferior_ptid);
 529   return beneath ()->core_of_thread (inferior_ptid);
 530 }
 531
 532 /* Observer on inferior_created: push ravenscar thread stratum if needed.  */
 533
 534 static void
 535 ravenscar_inferior_created (struct target_ops *target, int from_tty)
 536 {
 537   const char *err_msg;
 538
 539   if (!ravenscar_task_support
 540       || gdbarch_ravenscar_ops (target_gdbarch ()) == NULL
 541       || !has_ravenscar_runtime ())
 542     return;
 543
 544   err_msg = ada_get_tcb_types_info ();
 545   if (err_msg != NULL)
 546     {
 547       warning (_("%s. Task/thread support disabled."), err_msg);
 548       return;
 549     }
 550
 551   target_ops_up target_holder (new ravenscar_thread_target ());
 552   push_target (std::move (target_holder));
 553 }
 554
 555 ptid_t
 556 ravenscar_thread_target::get_ada_task_ptid (long lwp, long thread)
 557 {
 558   return ptid_t (m_base_ptid.pid (), 0, thread);
 559 }
 560
 561 /* Command-list for the "set/show ravenscar" prefix command.  */
 562 static struct cmd_list_element *set_ravenscar_list;
 563 static struct cmd_list_element *show_ravenscar_list;
 564
 565 /* Implement the "show ravenscar task-switching" command.  */
 566
 567 static void
 568 show_ravenscar_task_switching_command (struct ui_file *file, int from_tty,
 569                                        struct cmd_list_element *c,
 570                                        const char *value)
 571 {
 572   if (ravenscar_task_support)
 573     fprintf_filtered (file, _("\
 574 Support for Ravenscar task/thread switching is enabled\n"));
 575   else
 576     fprintf_filtered (file, _("\
 577 Support for Ravenscar task/thread switching is disabled\n"));
 578 }
 579
 580 /* Module startup initialization function, automagically called by
 581    init.c.  */
 582
 583 void _initialize_ravenscar ();
 584 void
 585 _initialize_ravenscar ()
 586 {
 587   /* Notice when the inferior is created in order to push the
 588      ravenscar ops if needed.  */
 589   gdb::observers::inferior_created.attach (ravenscar_inferior_created);
 590
 591   add_basic_prefix_cmd ("ravenscar", no_class,
 592                         _("Prefix command for changing Ravenscar-specific settings."),
 593                         &set_ravenscar_list, "set ravenscar ", 0, &setlist);
 594
 595   add_show_prefix_cmd ("ravenscar", no_class,
 596                        _("Prefix command for showing Ravenscar-specific settings."),
 597                        &show_ravenscar_list, "show ravenscar ", 0, &showlist);
 598
 599   add_setshow_boolean_cmd ("task-switching", class_obscure,
 600                            &ravenscar_task_support, _("\
 601 Enable or disable support for GNAT Ravenscar tasks."), _("\
 602 Show whether support for GNAT Ravenscar tasks is enabled."),
 603                            _("\
 604 Enable or disable support for task/thread switching with the GNAT\n\
 605 Ravenscar run-time library for bareboard configuration."),
 606                            NULL, show_ravenscar_task_switching_command,
 607                            &set_ravenscar_list, &show_ravenscar_list);
 608 }