gdb/dummy-frame.c

   1 /* Code dealing with dummy stack frames, for GDB, the GNU debugger.
   2
   3    Copyright (C) 1986-2021 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
  21 #include "defs.h"
  22 #include "dummy-frame.h"
  23 #include "regcache.h"
  24 #include "frame.h"
  25 #include "inferior.h"
  26 #include "frame-unwind.h"
  27 #include "command.h"
  28 #include "gdbcmd.h"
  29 #include "observable.h"
  30 #include "gdbthread.h"
  31 #include "infcall.h"
  32 #include "gdbarch.h"
  33
  34 struct dummy_frame_id
  35 {
  36   /* This frame's ID.  Must match the value returned by
  37      gdbarch_dummy_id.  */
  38   struct frame_id id;
  39
  40   /* The thread this dummy_frame relates to.  */
  41   thread_info *thread;
  42 };
  43
  44 /* Return whether dummy_frame_id *ID1 and *ID2 are equal.  */
  45
  46 static int
  47 dummy_frame_id_eq (struct dummy_frame_id *id1,
  48                    struct dummy_frame_id *id2)
  49 {
  50   return frame_id_eq (id1->id, id2->id) && id1->thread == id2->thread;
  51 }
  52
  53 /* List of dummy_frame destructors.  */
  54
  55 struct dummy_frame_dtor_list
  56 {
  57   /* Next element in the list or NULL if this is the last element.  */
  58   struct dummy_frame_dtor_list *next;
  59
  60   /* If non-NULL, a destructor that is run when this dummy frame is freed.  */
  61   dummy_frame_dtor_ftype *dtor;
  62
  63   /* Arbitrary data that is passed to DTOR.  */
  64   void *dtor_data;
  65 };
  66
  67 /* Dummy frame.  This saves the processor state just prior to setting
  68    up the inferior function call.  Older targets save the registers
  69    on the target stack (but that really slows down function calls).  */
  70
  71 struct dummy_frame
  72 {
  73   struct dummy_frame *next;
  74
  75   /* An id represents a dummy frame.  */
  76   struct dummy_frame_id id;
  77
  78   /* The caller's state prior to the call.  */
  79   struct infcall_suspend_state *caller_state;
  80
  81   /* First element of destructors list or NULL if there are no
  82      destructors registered for this dummy_frame.  */
  83   struct dummy_frame_dtor_list *dtor_list;
  84 };
  85
  86 static struct dummy_frame *dummy_frame_stack = NULL;
  87
  88 /* Push the caller's state, along with the dummy frame info, onto the
  89    dummy-frame stack.  */
  90
  91 void
  92 dummy_frame_push (struct infcall_suspend_state *caller_state,
  93                   const frame_id *dummy_id, thread_info *thread)
  94 {
  95   struct dummy_frame *dummy_frame;
  96
  97   dummy_frame = XCNEW (struct dummy_frame);
  98   dummy_frame->caller_state = caller_state;
  99   dummy_frame->id.id = (*dummy_id);
 100   dummy_frame->id.thread = thread;
 101   dummy_frame->next = dummy_frame_stack;
 102   dummy_frame_stack = dummy_frame;
 103 }
 104
 105 /* Remove *DUMMY_PTR from the dummy frame stack.  */
 106
 107 static void
 108 remove_dummy_frame (struct dummy_frame **dummy_ptr)
 109 {
 110   struct dummy_frame *dummy = *dummy_ptr;
 111
 112   while (dummy->dtor_list != NULL)
 113     {
 114       struct dummy_frame_dtor_list *list = dummy->dtor_list;
 115
 116       dummy->dtor_list = list->next;
 117       list->dtor (list->dtor_data, 0);
 118       xfree (list);
 119     }
 120
 121   *dummy_ptr = dummy->next;
 122   discard_infcall_suspend_state (dummy->caller_state);
 123   xfree (dummy);
 124 }
 125
 126 /* Delete any breakpoint B which is a momentary breakpoint for return from
 127    inferior call matching DUMMY_VOIDP.  */
 128
 129 static bool
 130 pop_dummy_frame_bpt (struct breakpoint *b, struct dummy_frame *dummy)
 131 {
 132   if (b->thread == dummy->id.thread->global_num
 133       && b->disposition == disp_del && frame_id_eq (b->frame_id, dummy->id.id))
 134     {
 135       while (b->related_breakpoint != b)
 136         delete_breakpoint (b->related_breakpoint);
 137
 138       delete_breakpoint (b);
 139
 140       /* Stop the traversal.  */
 141       return true;
 142     }
 143
 144   /* Continue the traversal.  */
 145   return false;
 146 }
 147
 148 /* Pop *DUMMY_PTR, restoring program state to that before the
 149    frame was created.  */
 150
 151 static void
 152 pop_dummy_frame (struct dummy_frame **dummy_ptr)
 153 {
 154   struct dummy_frame *dummy = *dummy_ptr;
 155
 156   gdb_assert (dummy->id.thread == inferior_thread ());
 157
 158   while (dummy->dtor_list != NULL)
 159     {
 160       struct dummy_frame_dtor_list *list = dummy->dtor_list;
 161
 162       dummy->dtor_list = list->next;
 163       list->dtor (list->dtor_data, 1);
 164       xfree (list);
 165     }
 166
 167   restore_infcall_suspend_state (dummy->caller_state);
 168
 169   for (breakpoint *bp : all_breakpoints_safe ())
 170     if (pop_dummy_frame_bpt (bp, dummy))
 171       break;
 172
 173   /* restore_infcall_control_state frees inf_state,
 174      all that remains is to pop *dummy_ptr.  */
 175   *dummy_ptr = dummy->next;
 176   xfree (dummy);
 177
 178   /* We've made right mess of GDB's local state, just discard
 179      everything.  */
 180   reinit_frame_cache ();
 181 }
 182
 183 /* Look up DUMMY_ID.
 184    Return NULL if not found.  */
 185
 186 static struct dummy_frame **
 187 lookup_dummy_frame (struct dummy_frame_id *dummy_id)
 188 {
 189   struct dummy_frame **dp;
 190
 191   for (dp = &dummy_frame_stack; *dp != NULL; dp = &(*dp)->next)
 192     {
 193       if (dummy_frame_id_eq (&(*dp)->id, dummy_id))
 194         return dp;
 195     }
 196
 197   return NULL;
 198 }
 199
 200 /* Find the dummy frame by DUMMY_ID and THREAD, and pop it, restoring
 201    program state to that before the frame was created.
 202    On return reinit_frame_cache has been called.
 203    If the frame isn't found, flag an internal error.  */
 204
 205 void
 206 dummy_frame_pop (frame_id dummy_id, thread_info *thread)
 207 {
 208   struct dummy_frame **dp;
 209   struct dummy_frame_id id = { dummy_id, thread };
 210
 211   dp = lookup_dummy_frame (&id);
 212   gdb_assert (dp != NULL);
 213
 214   pop_dummy_frame (dp);
 215 }
 216
 217 /* Find the dummy frame by DUMMY_ID and PTID and drop it.  Do nothing
 218    if it is not found.  Do not restore its state into inferior, just
 219    free its memory.  */
 220
 221 void
 222 dummy_frame_discard (struct frame_id dummy_id, thread_info *thread)
 223 {
 224   struct dummy_frame **dp;
 225   struct dummy_frame_id id = { dummy_id, thread };
 226
 227   dp = lookup_dummy_frame (&id);
 228   if (dp)
 229     remove_dummy_frame (dp);
 230 }
 231
 232 /* See dummy-frame.h.  */
 233
 234 void
 235 register_dummy_frame_dtor (frame_id dummy_id, thread_info *thread,
 236                            dummy_frame_dtor_ftype *dtor, void *dtor_data)
 237 {
 238   struct dummy_frame_id id = { dummy_id, thread };
 239   struct dummy_frame **dp, *d;
 240   struct dummy_frame_dtor_list *list;
 241
 242   dp = lookup_dummy_frame (&id);
 243   gdb_assert (dp != NULL);
 244   d = *dp;
 245   list = XNEW (struct dummy_frame_dtor_list);
 246   list->next = d->dtor_list;
 247   d->dtor_list = list;
 248   list->dtor = dtor;
 249   list->dtor_data = dtor_data;
 250 }
 251
 252 /* See dummy-frame.h.  */
 253
 254 int
 255 find_dummy_frame_dtor (dummy_frame_dtor_ftype *dtor, void *dtor_data)
 256 {
 257   struct dummy_frame *d;
 258
 259   for (d = dummy_frame_stack; d != NULL; d = d->next)
 260     {
 261       struct dummy_frame_dtor_list *list;
 262
 263       for (list = d->dtor_list; list != NULL; list = list->next)
 264         if (list->dtor == dtor && list->dtor_data == dtor_data)
 265           return 1;
 266     }
 267   return 0;
 268 }
 269
 270 /* There may be stale dummy frames, perhaps left over from when an uncaught
 271    longjmp took us out of a function that was called by the debugger.  Clean
 272    them up at least once whenever we start a new inferior.  */
 273
 274 static void
 275 cleanup_dummy_frames (inferior *inf)
 276 {
 277   while (dummy_frame_stack != NULL)
 278     remove_dummy_frame (&dummy_frame_stack);
 279 }
 280
 281 /* Return the dummy frame cache, it contains both the ID, and a
 282    pointer to the regcache.  */
 283 struct dummy_frame_cache
 284 {
 285   struct frame_id this_id;
 286   readonly_detached_regcache *prev_regcache;
 287 };
 288
 289 static int
 290 dummy_frame_sniffer (const struct frame_unwind *self,
 291                      struct frame_info *this_frame,
 292                      void **this_prologue_cache)
 293 {
 294   /* When unwinding a normal frame, the stack structure is determined
 295      by analyzing the frame's function's code (be it using brute force
 296      prologue analysis, or the dwarf2 CFI).  In the case of a dummy
 297      frame, that simply isn't possible.  The PC is either the program
 298      entry point, or some random address on the stack.  Trying to use
 299      that PC to apply standard frame ID unwind techniques is just
 300      asking for trouble.  */
 301
 302   /* Don't bother unless there is at least one dummy frame.  */
 303   if (dummy_frame_stack != NULL)
 304     {
 305       struct dummy_frame *dummyframe;
 306       /* Use an architecture specific method to extract this frame's
 307          dummy ID, assuming it is a dummy frame.  */
 308       struct frame_id this_id
 309         = gdbarch_dummy_id (get_frame_arch (this_frame), this_frame);
 310       struct dummy_frame_id dummy_id = { this_id, inferior_thread () };
 311
 312       /* Use that ID to find the corresponding cache entry.  */
 313       for (dummyframe = dummy_frame_stack;
 314            dummyframe != NULL;
 315            dummyframe = dummyframe->next)
 316         {
 317           if (dummy_frame_id_eq (&dummyframe->id, &dummy_id))
 318             {
 319               struct dummy_frame_cache *cache;
 320
 321               cache = FRAME_OBSTACK_ZALLOC (struct dummy_frame_cache);
 322               cache->prev_regcache = get_infcall_suspend_state_regcache
 323                                                    (dummyframe->caller_state);
 324               cache->this_id = this_id;
 325               (*this_prologue_cache) = cache;
 326               return 1;
 327             }
 328         }
 329     }
 330   return 0;
 331 }
 332
 333 /* Given a call-dummy dummy-frame, return the registers.  Here the
 334    register value is taken from the local copy of the register buffer.  */
 335
 336 static struct value *
 337 dummy_frame_prev_register (struct frame_info *this_frame,
 338                            void **this_prologue_cache,
 339                            int regnum)
 340 {
 341   struct dummy_frame_cache *cache
 342     = (struct dummy_frame_cache *) *this_prologue_cache;
 343   struct gdbarch *gdbarch = get_frame_arch (this_frame);
 344   struct value *reg_val;
 345
 346   /* The dummy-frame sniffer always fills in the cache.  */
 347   gdb_assert (cache != NULL);
 348
 349   /* Describe the register's location.  Generic dummy frames always
 350      have the register value in an ``expression''.  */
 351   reg_val = value_zero (register_type (gdbarch, regnum), not_lval);
 352
 353   /* Use the regcache_cooked_read() method so that it, on the fly,
 354      constructs either a raw or pseudo register from the raw
 355      register cache.  */
 356   cache->prev_regcache->cooked_read (regnum,
 357                                      value_contents_writeable (reg_val));
 358   return reg_val;
 359 }
 360
 361 /* Assuming that THIS_FRAME is a dummy, return its ID.  That ID is
 362    determined by examining the NEXT frame's unwound registers using
 363    the method dummy_id().  As a side effect, THIS dummy frame's
 364    dummy cache is located and saved in THIS_PROLOGUE_CACHE.  */
 365
 366 static void
 367 dummy_frame_this_id (struct frame_info *this_frame,
 368                      void **this_prologue_cache,
 369                      struct frame_id *this_id)
 370 {
 371   /* The dummy-frame sniffer always fills in the cache.  */
 372   struct dummy_frame_cache *cache
 373     = (struct dummy_frame_cache *) *this_prologue_cache;
 374
 375   gdb_assert (cache != NULL);
 376   (*this_id) = cache->this_id;
 377 }
 378
 379 const struct frame_unwind dummy_frame_unwind =
 380 {
 381   DUMMY_FRAME,
 382   default_frame_unwind_stop_reason,
 383   dummy_frame_this_id,
 384   dummy_frame_prev_register,
 385   NULL,
 386   dummy_frame_sniffer,
 387 };
 388
 389 /* See dummy-frame.h.  */
 390
 391 struct frame_id
 392 default_dummy_id (struct gdbarch *gdbarch, struct frame_info *this_frame)
 393 {
 394   CORE_ADDR sp, pc;
 395
 396   sp = get_frame_sp (this_frame);
 397   pc = get_frame_pc (this_frame);
 398   return frame_id_build (sp, pc);
 399 }
 400
 401 static void
 402 fprint_dummy_frames (struct ui_file *file)
 403 {
 404   struct dummy_frame *s;
 405
 406   for (s = dummy_frame_stack; s != NULL; s = s->next)
 407     {
 408       gdb_print_host_address (s, file);
 409       fprintf_unfiltered (file, ":");
 410       fprintf_unfiltered (file, " id=%s", s->id.id.to_string ().c_str ());
 411       fprintf_unfiltered (file, ", ptid=%s",
 412                           target_pid_to_str (s->id.thread->ptid).c_str ());
 413       fprintf_unfiltered (file, "\n");
 414     }
 415 }
 416
 417 static void
 418 maintenance_print_dummy_frames (const char *args, int from_tty)
 419 {
 420   if (args == NULL)
 421     fprint_dummy_frames (gdb_stdout);
 422   else
 423     {
 424       stdio_file file;
 425
 426       if (!file.open (args, "w"))
 427         perror_with_name (_("maintenance print dummy-frames"));
 428       fprint_dummy_frames (&file);
 429     }
 430 }
 431
 432 void _initialize_dummy_frame ();
 433 void
 434 _initialize_dummy_frame ()
 435 {
 436   add_cmd ("dummy-frames", class_maintenance, maintenance_print_dummy_frames,
 437            _("Print the contents of the internal dummy-frame stack."),
 438            &maintenanceprintlist);
 439
 440   gdb::observers::inferior_created.attach (cleanup_dummy_frames, "dummy-frame");
 441 }