gdb/dummy-frame.c

   1 /* Code dealing with dummy stack frames, for GDB, the GNU debugger.
   2
   3    Copyright (C) 1986-2020 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
  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   iterate_over_breakpoints ([dummy] (breakpoint* bp)
 170     {
 171       return pop_dummy_frame_bpt (bp, dummy);
 172     });
 173
 174   /* restore_infcall_control_state frees inf_state,
 175      all that remains is to pop *dummy_ptr.  */
 176   *dummy_ptr = dummy->next;
 177   xfree (dummy);
 178
 179   /* We've made right mess of GDB's local state, just discard
 180      everything.  */
 181   reinit_frame_cache ();
 182 }
 183
 184 /* Look up DUMMY_ID.
 185    Return NULL if not found.  */
 186
 187 static struct dummy_frame **
 188 lookup_dummy_frame (struct dummy_frame_id *dummy_id)
 189 {
 190   struct dummy_frame **dp;
 191
 192   for (dp = &dummy_frame_stack; *dp != NULL; dp = &(*dp)->next)
 193     {
 194       if (dummy_frame_id_eq (&(*dp)->id, dummy_id))
 195         return dp;
 196     }
 197
 198   return NULL;
 199 }
 200
 201 /* Find the dummy frame by DUMMY_ID and THREAD, and pop it, restoring
 202    program state to that before the frame was created.
 203    On return reinit_frame_cache has been called.
 204    If the frame isn't found, flag an internal error.  */
 205
 206 void
 207 dummy_frame_pop (frame_id dummy_id, thread_info *thread)
 208 {
 209   struct dummy_frame **dp;
 210   struct dummy_frame_id id = { dummy_id, thread };
 211
 212   dp = lookup_dummy_frame (&id);
 213   gdb_assert (dp != NULL);
 214
 215   pop_dummy_frame (dp);
 216 }
 217
 218 /* Find the dummy frame by DUMMY_ID and PTID and drop it.  Do nothing
 219    if it is not found.  Do not restore its state into inferior, just
 220    free its memory.  */
 221
 222 void
 223 dummy_frame_discard (struct frame_id dummy_id, thread_info *thread)
 224 {
 225   struct dummy_frame **dp;
 226   struct dummy_frame_id id = { dummy_id, thread };
 227
 228   dp = lookup_dummy_frame (&id);
 229   if (dp)
 230     remove_dummy_frame (dp);
 231 }
 232
 233 /* See dummy-frame.h.  */
 234
 235 void
 236 register_dummy_frame_dtor (frame_id dummy_id, thread_info *thread,
 237                            dummy_frame_dtor_ftype *dtor, void *dtor_data)
 238 {
 239   struct dummy_frame_id id = { dummy_id, thread };
 240   struct dummy_frame **dp, *d;
 241   struct dummy_frame_dtor_list *list;
 242
 243   dp = lookup_dummy_frame (&id);
 244   gdb_assert (dp != NULL);
 245   d = *dp;
 246   list = XNEW (struct dummy_frame_dtor_list);
 247   list->next = d->dtor_list;
 248   d->dtor_list = list;
 249   list->dtor = dtor;
 250   list->dtor_data = dtor_data;
 251 }
 252
 253 /* See dummy-frame.h.  */
 254
 255 int
 256 find_dummy_frame_dtor (dummy_frame_dtor_ftype *dtor, void *dtor_data)
 257 {
 258   struct dummy_frame *d;
 259
 260   for (d = dummy_frame_stack; d != NULL; d = d->next)
 261     {
 262       struct dummy_frame_dtor_list *list;
 263
 264       for (list = d->dtor_list; list != NULL; list = list->next)
 265         if (list->dtor == dtor && list->dtor_data == dtor_data)
 266           return 1;
 267     }
 268   return 0;
 269 }
 270
 271 /* There may be stale dummy frames, perhaps left over from when an uncaught
 272    longjmp took us out of a function that was called by the debugger.  Clean
 273    them up at least once whenever we start a new inferior.  */
 274
 275 static void
 276 cleanup_dummy_frames (struct target_ops *target, int from_tty)
 277 {
 278   while (dummy_frame_stack != NULL)
 279     remove_dummy_frame (&dummy_frame_stack);
 280 }
 281
 282 /* Return the dummy frame cache, it contains both the ID, and a
 283    pointer to the regcache.  */
 284 struct dummy_frame_cache
 285 {
 286   struct frame_id this_id;
 287   readonly_detached_regcache *prev_regcache;
 288 };
 289
 290 static int
 291 dummy_frame_sniffer (const struct frame_unwind *self,
 292                      struct frame_info *this_frame,
 293                      void **this_prologue_cache)
 294 {
 295   /* When unwinding a normal frame, the stack structure is determined
 296      by analyzing the frame's function's code (be it using brute force
 297      prologue analysis, or the dwarf2 CFI).  In the case of a dummy
 298      frame, that simply isn't possible.  The PC is either the program
 299      entry point, or some random address on the stack.  Trying to use
 300      that PC to apply standard frame ID unwind techniques is just
 301      asking for trouble.  */
 302
 303   /* Don't bother unless there is at least one dummy frame.  */
 304   if (dummy_frame_stack != NULL)
 305     {
 306       struct dummy_frame *dummyframe;
 307       /* Use an architecture specific method to extract this frame's
 308          dummy ID, assuming it is a dummy frame.  */
 309       struct frame_id this_id
 310         = gdbarch_dummy_id (get_frame_arch (this_frame), this_frame);
 311       struct dummy_frame_id dummy_id = { this_id, inferior_thread () };
 312
 313       /* Use that ID to find the corresponding cache entry.  */
 314       for (dummyframe = dummy_frame_stack;
 315            dummyframe != NULL;
 316            dummyframe = dummyframe->next)
 317         {
 318           if (dummy_frame_id_eq (&dummyframe->id, &dummy_id))
 319             {
 320               struct dummy_frame_cache *cache;
 321
 322               cache = FRAME_OBSTACK_ZALLOC (struct dummy_frame_cache);
 323               cache->prev_regcache = get_infcall_suspend_state_regcache
 324                                                    (dummyframe->caller_state);
 325               cache->this_id = this_id;
 326               (*this_prologue_cache) = cache;
 327               return 1;
 328             }
 329         }
 330     }
 331   return 0;
 332 }
 333
 334 /* Given a call-dummy dummy-frame, return the registers.  Here the
 335    register value is taken from the local copy of the register buffer.  */
 336
 337 static struct value *
 338 dummy_frame_prev_register (struct frame_info *this_frame,
 339                            void **this_prologue_cache,
 340                            int regnum)
 341 {
 342   struct dummy_frame_cache *cache
 343     = (struct dummy_frame_cache *) *this_prologue_cache;
 344   struct gdbarch *gdbarch = get_frame_arch (this_frame);
 345   struct value *reg_val;
 346
 347   /* The dummy-frame sniffer always fills in the cache.  */
 348   gdb_assert (cache != NULL);
 349
 350   /* Describe the register's location.  Generic dummy frames always
 351      have the register value in an ``expression''.  */
 352   reg_val = value_zero (register_type (gdbarch, regnum), not_lval);
 353
 354   /* Use the regcache_cooked_read() method so that it, on the fly,
 355      constructs either a raw or pseudo register from the raw
 356      register cache.  */
 357   cache->prev_regcache->cooked_read (regnum,
 358                                      value_contents_writeable (reg_val));
 359   return reg_val;
 360 }
 361
 362 /* Assuming that THIS_FRAME is a dummy, return its ID.  That ID is
 363    determined by examining the NEXT frame's unwound registers using
 364    the method dummy_id().  As a side effect, THIS dummy frame's
 365    dummy cache is located and saved in THIS_PROLOGUE_CACHE.  */
 366
 367 static void
 368 dummy_frame_this_id (struct frame_info *this_frame,
 369                      void **this_prologue_cache,
 370                      struct frame_id *this_id)
 371 {
 372   /* The dummy-frame sniffer always fills in the cache.  */
 373   struct dummy_frame_cache *cache
 374     = (struct dummy_frame_cache *) *this_prologue_cache;
 375
 376   gdb_assert (cache != NULL);
 377   (*this_id) = cache->this_id;
 378 }
 379
 380 const struct frame_unwind dummy_frame_unwind =
 381 {
 382   DUMMY_FRAME,
 383   default_frame_unwind_stop_reason,
 384   dummy_frame_this_id,
 385   dummy_frame_prev_register,
 386   NULL,
 387   dummy_frame_sniffer,
 388 };
 389
 390 /* See dummy-frame.h.  */
 391
 392 struct frame_id
 393 default_dummy_id (struct gdbarch *gdbarch, struct frame_info *this_frame)
 394 {
 395   CORE_ADDR sp, pc;
 396
 397   sp = get_frame_sp (this_frame);
 398   pc = get_frame_pc (this_frame);
 399   return frame_id_build (sp, pc);
 400 }
 401
 402 static void
 403 fprint_dummy_frames (struct ui_file *file)
 404 {
 405   struct dummy_frame *s;
 406
 407   for (s = dummy_frame_stack; s != NULL; s = s->next)
 408     {
 409       gdb_print_host_address (s, file);
 410       fprintf_unfiltered (file, ":");
 411       fprintf_unfiltered (file, " id=");
 412       fprint_frame_id (file, s->id.id);
 413       fprintf_unfiltered (file, ", ptid=%s",
 414                           target_pid_to_str (s->id.thread->ptid).c_str ());
 415       fprintf_unfiltered (file, "\n");
 416     }
 417 }
 418
 419 static void
 420 maintenance_print_dummy_frames (const char *args, int from_tty)
 421 {
 422   if (args == NULL)
 423     fprint_dummy_frames (gdb_stdout);
 424   else
 425     {
 426       stdio_file file;
 427
 428       if (!file.open (args, "w"))
 429         perror_with_name (_("maintenance print dummy-frames"));
 430       fprint_dummy_frames (&file);
 431     }
 432 }
 433
 434 void _initialize_dummy_frame ();
 435 void
 436 _initialize_dummy_frame ()
 437 {
 438   add_cmd ("dummy-frames", class_maintenance, maintenance_print_dummy_frames,
 439            _("Print the contents of the internal dummy-frame stack."),
 440            &maintenanceprintlist);
 441
 442   gdb::observers::inferior_created.attach (cleanup_dummy_frames);
 443 }