gdb/dummy-frame.c

   1 /* Code dealing with dummy stack frames, for GDB, the GNU debugger.
   2
   3    Copyright 1986, 1987, 1988, 1989, 1990, 1991, 1992, 1993, 1994,
   4    1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002 Free Software
   5    Foundation, Inc.
   6
   7    This file is part of GDB.
   8
   9    This program is free software; you can redistribute it and/or modify
  10    it under the terms of the GNU General Public License as published by
  11    the Free Software Foundation; either version 2 of the License, or
  12    (at your option) any later version.
  13
  14    This program is distributed in the hope that it will be useful,
  15    but WITHOUT ANY WARRANTY; without even the implied warranty of
  16    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  17    GNU General Public License for more details.
  18
  19    You should have received a copy of the GNU General Public License
  20    along with this program; if not, write to the Free Software
  21    Foundation, Inc., 59 Temple Place - Suite 330,
  22    Boston, MA 02111-1307, USA.  */
  23
  24
  25 #include "defs.h"
  26 #include "dummy-frame.h"
  27 #include "regcache.h"
  28 #include "frame.h"
  29 #include "inferior.h"
  30 #include "gdb_assert.h"
  31 #include "frame-unwind.h"
  32
  33 static void dummy_frame_this_id (struct frame_info *next_frame,
  34                                  void **this_prologue_cache,
  35                                  struct frame_id *this_id);
  36
  37 /* Dummy frame.  This saves the processor state just prior to setting
  38    up the inferior function call.  Older targets save the registers
  39    on the target stack (but that really slows down function calls).  */
  40
  41 struct dummy_frame
  42 {
  43   struct dummy_frame *next;
  44
  45   /* These values belong to the caller (the previous frame, the frame
  46      that this unwinds back to).  */
  47   CORE_ADDR pc;
  48   CORE_ADDR fp;
  49   CORE_ADDR sp;
  50   CORE_ADDR top;
  51   struct frame_id id;
  52   struct regcache *regcache;
  53
  54   /* Address range of the call dummy code.  Look for PC in the range
  55      [LO..HI) (after allowing for DECR_PC_AFTER_BREAK).  */
  56   CORE_ADDR call_lo;
  57   CORE_ADDR call_hi;
  58 };
  59
  60 static struct dummy_frame *dummy_frame_stack = NULL;
  61
  62 /* Function: find_dummy_frame(pc, fp, sp)
  63
  64    Search the stack of dummy frames for one matching the given PC and
  65    FP/SP.  Unlike pc_in_dummy_frame(), this function doesn't need to
  66    adjust for DECR_PC_AFTER_BREAK.  This is because it is only legal
  67    to call this function after the PC has been adjusted.  */
  68
  69 static struct dummy_frame *
  70 find_dummy_frame (CORE_ADDR pc, CORE_ADDR fp)
  71 {
  72   struct dummy_frame *dummyframe;
  73
  74   for (dummyframe = dummy_frame_stack; dummyframe != NULL;
  75        dummyframe = dummyframe->next)
  76     {
  77       /* Does the PC fall within the dummy frame's breakpoint
  78          instruction.  If not, discard this one.  */
  79       if (!(pc >= dummyframe->call_lo && pc < dummyframe->call_hi))
  80         continue;
  81       /* Does the FP match?  */
  82       if (dummyframe->top != 0)
  83         {
  84           /* If the target architecture explicitly saved the
  85              top-of-stack before the inferior function call, assume
  86              that that same architecture will always pass in an FP
  87              (frame base) value that eactly matches that saved TOS.
  88              Don't check the saved SP and SP as they can lead to false
  89              hits.  */
  90           if (fp != dummyframe->top)
  91             continue;
  92         }
  93       else
  94         {
  95           /* An older target that hasn't explicitly or implicitly
  96              saved the dummy frame's top-of-stack.  Try matching the
  97              FP against the saved SP and FP.  NOTE: If you're trying
  98              to fix a problem with GDB not correctly finding a dummy
  99              frame, check the comments that go with FRAME_ALIGN() and
 100              SAVE_DUMMY_FRAME_TOS().  */
 101           if (fp != dummyframe->fp && fp != dummyframe->sp)
 102             continue;
 103         }
 104       /* The FP matches this dummy frame.  */
 105       return dummyframe;
 106     }
 107
 108   return NULL;
 109 }
 110
 111 struct regcache *
 112 generic_find_dummy_frame (CORE_ADDR pc, CORE_ADDR fp)
 113 {
 114   struct dummy_frame *dummy = find_dummy_frame (pc, fp);
 115   if (dummy != NULL)
 116     return dummy->regcache;
 117   else
 118     return NULL;
 119 }
 120
 121 char *
 122 deprecated_generic_find_dummy_frame (CORE_ADDR pc, CORE_ADDR fp)
 123 {
 124   struct regcache *regcache = generic_find_dummy_frame (pc, fp);
 125   if (regcache == NULL)
 126     return NULL;
 127   return deprecated_grub_regcache_for_registers (regcache);
 128 }
 129
 130 /* Function: pc_in_call_dummy (pc, sp, fp)
 131
 132    Return true if the PC falls in a dummy frame created by gdb for an
 133    inferior call.  The code below which allows DECR_PC_AFTER_BREAK is
 134    for infrun.c, which may give the function a PC without that
 135    subtracted out.  */
 136
 137 int
 138 generic_pc_in_call_dummy (CORE_ADDR pc, CORE_ADDR sp, CORE_ADDR fp)
 139 {
 140   return pc_in_dummy_frame (pc);
 141 }
 142
 143 /* Return non-zero if the PC falls in a dummy frame.
 144
 145    The code below which allows DECR_PC_AFTER_BREAK is for infrun.c,
 146    which may give the function a PC without that subtracted out.
 147
 148    FIXME: cagney/2002-11-23: This is silly.  Surely "infrun.c" can
 149    figure out what the real PC (as in the resume address) is BEFORE
 150    calling this function (Oh, and I'm not even sure that this function
 151    is called with an decremented PC, the call to pc_in_call_dummy() in
 152    that file is conditional on !CALL_DUMMY_BREAKPOINT_OFFSET_P yet
 153    generic dummy targets set CALL_DUMMY_BREAKPOINT_OFFSET. True?).  */
 154
 155 int
 156 pc_in_dummy_frame (CORE_ADDR pc)
 157 {
 158   struct dummy_frame *dummyframe;
 159   for (dummyframe = dummy_frame_stack;
 160        dummyframe != NULL;
 161        dummyframe = dummyframe->next)
 162     {
 163       if ((pc >= dummyframe->call_lo)
 164           && (pc < dummyframe->call_hi + DECR_PC_AFTER_BREAK))
 165         return 1;
 166     }
 167   return 0;
 168 }
 169
 170 /* Function: read_register_dummy
 171    Find a saved register from before GDB calls a function in the inferior */
 172
 173 CORE_ADDR
 174 deprecated_read_register_dummy (CORE_ADDR pc, CORE_ADDR fp, int regno)
 175 {
 176   struct regcache *dummy_regs = generic_find_dummy_frame (pc, fp);
 177
 178   if (dummy_regs)
 179     {
 180       /* NOTE: cagney/2002-08-12: Replaced a call to
 181          regcache_raw_read_as_address() with a call to
 182          regcache_cooked_read_unsigned().  The old, ...as_address
 183          function was eventually calling extract_unsigned_integer (via
 184          extract_address) to unpack the registers value.  The below is
 185          doing an unsigned extract so that it is functionally
 186          equivalent.  The read needs to be cooked as, otherwise, it
 187          will never correctly return the value of a register in the
 188          [NUM_REGS .. NUM_REGS+NUM_PSEUDO_REGS) range.  */
 189       ULONGEST val;
 190       regcache_cooked_read_unsigned (dummy_regs, regno, &val);
 191       return val;
 192     }
 193   else
 194     return 0;
 195 }
 196
 197 /* Save all the registers on the dummy frame stack.  Most ports save the
 198    registers on the target stack.  This results in lots of unnecessary memory
 199    references, which are slow when debugging via a serial line.  Instead, we
 200    save all the registers internally, and never write them to the stack.  The
 201    registers get restored when the called function returns to the entry point,
 202    where a breakpoint is laying in wait.  */
 203
 204 void
 205 generic_push_dummy_frame (void)
 206 {
 207   struct dummy_frame *dummy_frame;
 208   CORE_ADDR fp = get_frame_base (get_current_frame ());
 209
 210   /* check to see if there are stale dummy frames,
 211      perhaps left over from when a longjump took us out of a
 212      function that was called by the debugger */
 213
 214   dummy_frame = dummy_frame_stack;
 215   while (dummy_frame)
 216     if (INNER_THAN (dummy_frame->fp, fp))       /* stale -- destroy! */
 217       {
 218         dummy_frame_stack = dummy_frame->next;
 219         regcache_xfree (dummy_frame->regcache);
 220         xfree (dummy_frame);
 221         dummy_frame = dummy_frame_stack;
 222       }
 223     else
 224       dummy_frame = dummy_frame->next;
 225
 226   dummy_frame = xmalloc (sizeof (struct dummy_frame));
 227   dummy_frame->regcache = regcache_xmalloc (current_gdbarch);
 228
 229   dummy_frame->pc = read_pc ();
 230   dummy_frame->sp = read_sp ();
 231   dummy_frame->top = 0;
 232   dummy_frame->fp = fp;
 233   dummy_frame->id = get_frame_id (get_current_frame ());
 234   regcache_cpy (dummy_frame->regcache, current_regcache);
 235   dummy_frame->next = dummy_frame_stack;
 236   dummy_frame_stack = dummy_frame;
 237 }
 238
 239 void
 240 generic_save_dummy_frame_tos (CORE_ADDR sp)
 241 {
 242   dummy_frame_stack->top = sp;
 243 }
 244
 245 /* Record the upper/lower bounds on the address of the call dummy.  */
 246
 247 void
 248 generic_save_call_dummy_addr (CORE_ADDR lo, CORE_ADDR hi)
 249 {
 250   dummy_frame_stack->call_lo = lo;
 251   dummy_frame_stack->call_hi = hi;
 252 }
 253
 254 /* Restore the machine state from either the saved dummy stack or a
 255    real stack frame. */
 256
 257 void
 258 generic_pop_current_frame (void (*popper) (struct frame_info * frame))
 259 {
 260   struct frame_info *frame = get_current_frame ();
 261   if (get_frame_type (frame) == DUMMY_FRAME)
 262     /* NOTE: cagney/2002-22-23: Does this ever occure?  Surely a dummy
 263        frame will have already been poped by the "infrun.c" code.  */
 264     generic_pop_dummy_frame ();
 265   else
 266     (*popper) (frame);
 267 }
 268
 269 /* Discard the innermost dummy frame from the dummy frame stack
 270    (passed in as a parameter).  */
 271
 272 static void
 273 discard_innermost_dummy (struct dummy_frame **stack)
 274 {
 275   struct dummy_frame *tbd = (*stack);
 276   (*stack) = (*stack)->next;
 277   regcache_xfree (tbd->regcache);
 278   xfree (tbd);
 279 }
 280
 281 void
 282 generic_pop_dummy_frame (void)
 283 {
 284   struct dummy_frame *dummy_frame = dummy_frame_stack;
 285
 286   /* FIXME: what if the first frame isn't the right one, eg..
 287      because one call-by-hand function has done a longjmp into another one? */
 288
 289   if (!dummy_frame)
 290     error ("Can't pop dummy frame!");
 291   regcache_cpy (current_regcache, dummy_frame->regcache);
 292   flush_cached_frames ();
 293
 294   discard_innermost_dummy (&dummy_frame_stack);
 295 }
 296
 297 /* Given a call-dummy dummy-frame, return the registers.  Here the
 298    register value is taken from the local copy of the register buffer.  */
 299
 300 static void
 301 dummy_frame_prev_register (struct frame_info *next_frame,
 302                            void **this_prologue_cache,
 303                            int regnum, int *optimized,
 304                            enum lval_type *lvalp, CORE_ADDR *addrp,
 305                            int *realnum, void *bufferp)
 306 {
 307   struct dummy_frame *dummy;
 308   struct frame_id id;
 309
 310   /* Call the ID method which, if at all possible, will set the
 311      prologue cache.  */
 312   dummy_frame_this_id (next_frame, this_prologue_cache, &id);
 313   dummy = (*this_prologue_cache);
 314   gdb_assert (dummy != NULL);
 315
 316   /* Describe the register's location.  Generic dummy frames always
 317      have the register value in an ``expression''.  */
 318   *optimized = 0;
 319   *lvalp = not_lval;
 320   *addrp = 0;
 321   *realnum = -1;
 322
 323   /* If needed, find and return the value of the register.  */
 324   if (bufferp != NULL)
 325     {
 326       /* Return the actual value.  */
 327       /* Use the regcache_cooked_read() method so that it, on the fly,
 328          constructs either a raw or pseudo register from the raw
 329          register cache.  */
 330       regcache_cooked_read (dummy->regcache, regnum, bufferp);
 331     }
 332 }
 333
 334 /* Assuming that THIS frame is a dummy (remember, the NEXT and not
 335    THIS frame is passed in), return the ID of THIS frame.  That ID is
 336    determined by examining the NEXT frame's unwound registers using
 337    the method unwind_dummy_id().  As a side effect, THIS dummy frame's
 338    dummy cache is located and and saved in THIS_PROLOGUE_CACHE.  */
 339
 340 static void
 341 dummy_frame_this_id (struct frame_info *next_frame,
 342                      void **this_prologue_cache,
 343                      struct frame_id *this_id)
 344 {
 345   struct dummy_frame *dummy = (*this_prologue_cache);
 346   if (dummy != NULL)
 347     {
 348       (*this_id) = dummy->id;
 349       return;
 350     }
 351   /* When unwinding a normal frame, the stack structure is determined
 352      by analyzing the frame's function's code (be it using brute force
 353      prologue analysis, or the dwarf2 CFI).  In the case of a dummy
 354      frame, that simply isn't possible.  The The PC is either the
 355      program entry point, or some random address on the stack.  Trying
 356      to use that PC to apply standard frame ID unwind techniques is
 357      just asking for trouble.  */
 358   if (gdbarch_unwind_dummy_id_p (current_gdbarch))
 359     {
 360       /* Assume call_function_by_hand(), via SAVE_DUMMY_FRAME_TOS,
 361          previously saved the dummy frame's ID.  Things only work if
 362          the two return the same value.  */
 363       gdb_assert (SAVE_DUMMY_FRAME_TOS_P ());
 364       /* Use an architecture specific method to extract the prev's
 365          dummy ID from the next frame.  Note that this method uses
 366          frame_register_unwind to obtain the register values needed to
 367          determine the dummy frame's ID.  */
 368       (*this_id) = gdbarch_unwind_dummy_id (current_gdbarch, next_frame);
 369     }
 370   else if (frame_relative_level (next_frame) < 0)
 371     {
 372       /* We're unwinding a sentinel frame, the PC of which is pointing
 373          at a stack dummy.  Fake up the dummy frame's ID using the
 374          same sequence as is found a traditional unwinder.  Once all
 375          architectures supply the unwind_dummy_id method, this code
 376          can go away.  */
 377       (*this_id) = frame_id_build (read_fp (), read_pc ());
 378     }
 379   else if (legacy_frame_p (current_gdbarch)
 380            && get_prev_frame (next_frame))
 381     {
 382       /* Things are looking seriously grim!  Assume that the legacy
 383          get_prev_frame code has already created THIS frame and linked
 384          it in to the frame chain (a pretty bold assumption), extract
 385          the ID from THIS base / pc.  */
 386       (*this_id) = frame_id_build (get_frame_base (get_prev_frame (next_frame)),
 387                                    get_frame_pc (get_prev_frame (next_frame)));
 388     }
 389   else
 390     {
 391       /* Outch!  We're not trying to find the innermost frame's ID yet
 392          we're trying to unwind to a dummy.  The architecture must
 393          provide the unwind_dummy_id() method.  Abandon the unwind
 394          process but only after first warning the user.  */
 395       internal_warning (__FILE__, __LINE__,
 396                         "Missing unwind_dummy_id architecture method");
 397       (*this_id) = null_frame_id;
 398       return;
 399     }
 400   (*this_prologue_cache) = find_dummy_frame ((*this_id).code_addr,
 401                                              (*this_id).stack_addr);
 402 }
 403
 404 static struct frame_unwind dummy_frame_unwind =
 405 {
 406   DUMMY_FRAME,
 407   dummy_frame_this_id,
 408   dummy_frame_prev_register
 409 };
 410
 411 const struct frame_unwind *
 412 dummy_frame_p (CORE_ADDR pc)
 413 {
 414   if (DEPRECATED_PC_IN_CALL_DUMMY_P ()
 415       ? DEPRECATED_PC_IN_CALL_DUMMY (pc, 0, 0)
 416       : pc_in_dummy_frame (pc))
 417     return &dummy_frame_unwind;
 418   else
 419     return NULL;
 420 }