gdb/ax-general.c

   1 /* Functions for manipulating expressions designed to be executed on the agent
   2    Copyright (C) 1998-2024 Free Software Foundation, Inc.
   3
   4    This file is part of GDB.
   5
   6    This program is free software; you can redistribute it and/or modify
   7    it under the terms of the GNU General Public License as published by
   8    the Free Software Foundation; either version 3 of the License, or
   9    (at your option) any later version.
  10
  11    This program is distributed in the hope that it will be useful,
  12    but WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14    GNU General Public License for more details.
  15
  16    You should have received a copy of the GNU General Public License
  17    along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
  18
  19 /* Despite what the above comment says about this file being part of
  20    GDB, we would like to keep these functions free of GDB
  21    dependencies, since we want to be able to use them in contexts
  22    outside of GDB (test suites, the stub, etc.)  */
  23
  24 #include "defs.h"
  25 #include "ax.h"
  26 #include "gdbarch.h"
  27
  28 #include "value.h"
  29 #include "user-regs.h"
  30
  31 static void append_const (struct agent_expr *x, LONGEST val, int n);
  32
  33 static LONGEST read_const (struct agent_expr *x, int o, int n);
  34
  35 static void generic_ext (struct agent_expr *x, enum agent_op op, int n);
  36 \f
  37 /* Functions for building expressions.  */
  38
  39 /* Append the low N bytes of VAL as an N-byte integer to the
  40    expression X, in big-endian order.  */
  41 static void
  42 append_const (struct agent_expr *x, LONGEST val, int n)
  43 {
  44   size_t len = x->buf.size ();
  45   x->buf.resize (len + n);
  46   for (int i = n - 1; i >= 0; i--)
  47     {
  48       x->buf[len + i] = val & 0xff;
  49       val >>= 8;
  50     }
  51 }
  52
  53
  54 /* Extract an N-byte big-endian unsigned integer from expression X at
  55    offset O.  */
  56 static LONGEST
  57 read_const (struct agent_expr *x, int o, int n)
  58 {
  59   int i;
  60   LONGEST accum = 0;
  61
  62   /* Make sure we're not reading off the end of the expression.  */
  63   if (o + n > x->buf.size ())
  64     error (_("GDB bug: ax-general.c (read_const): incomplete constant"));
  65
  66   for (i = 0; i < n; i++)
  67     accum = (accum << 8) | x->buf[o + i];
  68
  69   return accum;
  70 }
  71
  72 /* See ax.h.  */
  73
  74 void
  75 ax_raw_byte (struct agent_expr *x, gdb_byte byte)
  76 {
  77   x->buf.push_back (byte);
  78 }
  79
  80 /* Append a simple operator OP to EXPR.  */
  81 void
  82 ax_simple (struct agent_expr *x, enum agent_op op)
  83 {
  84   ax_raw_byte (x, op);
  85 }
  86
  87 /* Append a pick operator to EXPR.  DEPTH is the stack item to pick,
  88    with 0 being top of stack.  */
  89
  90 void
  91 ax_pick (struct agent_expr *x, int depth)
  92 {
  93   if (depth < 0 || depth > 255)
  94     error (_("GDB bug: ax-general.c (ax_pick): stack depth out of range"));
  95   ax_simple (x, aop_pick);
  96   append_const (x, 1, depth);
  97 }
  98
  99
 100 /* Append a sign-extension or zero-extension instruction to EXPR, to
 101    extend an N-bit value.  */
 102 static void
 103 generic_ext (struct agent_expr *x, enum agent_op op, int n)
 104 {
 105   /* N must fit in a byte.  */
 106   if (n < 0 || n > 255)
 107     error (_("GDB bug: ax-general.c (generic_ext): bit count out of range"));
 108   /* That had better be enough range.  */
 109   if (sizeof (LONGEST) * 8 > 255)
 110     error (_("GDB bug: ax-general.c (generic_ext): "
 111              "opcode has inadequate range"));
 112
 113   x->buf.push_back (op);
 114   x->buf.push_back (n);
 115 }
 116
 117
 118 /* Append a sign-extension instruction to EXPR, to extend an N-bit value.  */
 119 void
 120 ax_ext (struct agent_expr *x, int n)
 121 {
 122   generic_ext (x, aop_ext, n);
 123 }
 124
 125
 126 /* Append a zero-extension instruction to EXPR, to extend an N-bit value.  */
 127 void
 128 ax_zero_ext (struct agent_expr *x, int n)
 129 {
 130   generic_ext (x, aop_zero_ext, n);
 131 }
 132
 133
 134 /* Append a trace_quick instruction to EXPR, to record N bytes.  */
 135 void
 136 ax_trace_quick (struct agent_expr *x, int n)
 137 {
 138   /* N must fit in a byte.  */
 139   if (n < 0 || n > 255)
 140     error (_("GDB bug: ax-general.c (ax_trace_quick): "
 141              "size out of range for trace_quick"));
 142
 143   x->buf.push_back (aop_trace_quick);
 144   x->buf.push_back (n);
 145 }
 146
 147
 148 /* Append a goto op to EXPR.  OP is the actual op (must be aop_goto or
 149    aop_if_goto).  We assume we don't know the target offset yet,
 150    because it's probably a forward branch, so we leave space in EXPR
 151    for the target, and return the offset in EXPR of that space, so we
 152    can backpatch it once we do know the target offset.  Use ax_label
 153    to do the backpatching.  */
 154 int
 155 ax_goto (struct agent_expr *x, enum agent_op op)
 156 {
 157   x->buf.push_back (op);
 158   x->buf.push_back (0xff);
 159   x->buf.push_back (0xff);
 160   return x->buf.size () - 2;
 161 }
 162
 163 /* Suppose a given call to ax_goto returns some value PATCH.  When you
 164    know the offset TARGET that goto should jump to, call
 165    ax_label (EXPR, PATCH, TARGET)
 166    to patch TARGET into the ax_goto instruction.  */
 167 void
 168 ax_label (struct agent_expr *x, int patch, int target)
 169 {
 170   /* Make sure the value is in range.  Don't accept 0xffff as an
 171      offset; that's our magic sentinel value for unpatched branches.  */
 172   if (target < 0 || target >= 0xffff)
 173     error (_("GDB bug: ax-general.c (ax_label): label target out of range"));
 174
 175   x->buf[patch] = (target >> 8) & 0xff;
 176   x->buf[patch + 1] = target & 0xff;
 177 }
 178
 179
 180 /* Assemble code to push a constant on the stack.  */
 181 void
 182 ax_const_l (struct agent_expr *x, LONGEST l)
 183 {
 184   static enum agent_op ops[]
 185   =
 186   {aop_const8, aop_const16, aop_const32, aop_const64};
 187   int size;
 188   int op;
 189
 190   /* How big is the number?  'op' keeps track of which opcode to use.
 191      Notice that we don't really care whether the original number was
 192      signed or unsigned; we always reproduce the value exactly, and
 193      use the shortest representation.  */
 194   for (op = 0, size = 8; size < 64; size *= 2, op++)
 195     {
 196       LONGEST lim = ((LONGEST) 1) << (size - 1);
 197
 198       if (-lim <= l && l <= lim - 1)
 199         break;
 200     }
 201
 202   /* Emit the right opcode...  */
 203   ax_simple (x, ops[op]);
 204
 205   /* Emit the low SIZE bytes as an unsigned number.  We know that
 206      sign-extending this will yield l.  */
 207   append_const (x, l, size / 8);
 208
 209   /* Now, if it was negative, and not full-sized, sign-extend it.  */
 210   if (l < 0 && size < 64)
 211     ax_ext (x, size);
 212 }
 213
 214
 215 void
 216 ax_const_d (struct agent_expr *x, LONGEST d)
 217 {
 218   /* FIXME: floating-point support not present yet.  */
 219   error (_("GDB bug: ax-general.c (ax_const_d): "
 220            "floating point not supported yet"));
 221 }
 222
 223
 224 /* Assemble code to push the value of register number REG on the
 225    stack.  */
 226 void
 227 ax_reg (struct agent_expr *x, int reg)
 228 {
 229   if (reg >= gdbarch_num_regs (x->gdbarch))
 230     {
 231       /* This is a pseudo-register.  */
 232       if (!gdbarch_ax_pseudo_register_push_stack_p (x->gdbarch))
 233         error (_("'%s' is a pseudo-register; "
 234                  "GDB cannot yet trace its contents."),
 235                user_reg_map_regnum_to_name (x->gdbarch, reg));
 236       if (gdbarch_ax_pseudo_register_push_stack (x->gdbarch, x, reg))
 237         error (_("Trace '%s' failed."),
 238                user_reg_map_regnum_to_name (x->gdbarch, reg));
 239     }
 240   else
 241     {
 242       /* Get the remote register number.  */
 243       reg = gdbarch_remote_register_number (x->gdbarch, reg);
 244
 245       /* Make sure the register number is in range.  */
 246       if (reg < 0 || reg > 0xffff)
 247         error (_("GDB bug: ax-general.c (ax_reg): "
 248                  "register number out of range"));
 249       x->buf.push_back (aop_reg);
 250       x->buf.push_back ((reg >> 8) & 0xff);
 251       x->buf.push_back ((reg) & 0xff);
 252     }
 253 }
 254
 255 /* Assemble code to operate on a trace state variable.  */
 256
 257 void
 258 ax_tsv (struct agent_expr *x, enum agent_op op, int num)
 259 {
 260   /* Make sure the tsv number is in range.  */
 261   if (num < 0 || num > 0xffff)
 262     internal_error (_("ax-general.c (ax_tsv): variable "
 263                       "number is %d, out of range"), num);
 264
 265   x->buf.push_back (op);
 266   x->buf.push_back ((num >> 8) & 0xff);
 267   x->buf.push_back ((num) & 0xff);
 268 }
 269
 270 /* Append a string to the expression.  Note that the string is going
 271    into the bytecodes directly, not on the stack.  As a precaution,
 272    include both length as prefix, and terminate with a NUL.  (The NUL
 273    is counted in the length.)  */
 274
 275 void
 276 ax_string (struct agent_expr *x, const char *str, int slen)
 277 {
 278   int i;
 279
 280   /* Make sure the string length is reasonable.  */
 281   if (slen < 0 || slen > 0xffff)
 282     internal_error (_("ax-general.c (ax_string): string "
 283                       "length is %d, out of allowed range"), slen);
 284
 285   x->buf.push_back (((slen + 1) >> 8) & 0xff);
 286   x->buf.push_back ((slen + 1) & 0xff);
 287   for (i = 0; i < slen; ++i)
 288     x->buf.push_back (str[i]);
 289   x->buf.push_back ('\0');
 290 }
 291 \f
 292
 293
 294 /* Functions for disassembling agent expressions, and otherwise
 295    debugging the expression compiler.  */
 296
 297 /* An entry in the opcode map.  */
 298 struct aop_map
 299   {
 300
 301     /* The name of the opcode.  Null means that this entry is not a
 302        valid opcode --- a hole in the opcode space.  */
 303     const char *name;
 304
 305     /* All opcodes take no operands from the bytecode stream, or take
 306        unsigned integers of various sizes.  If this is a positive number
 307        n, then the opcode is followed by an n-byte operand, which should
 308        be printed as an unsigned integer.  If this is zero, then the
 309        opcode takes no operands from the bytecode stream.
 310
 311        If we get more complicated opcodes in the future, don't add other
 312        magic values of this; that's a crock.  Add an `enum encoding'
 313        field to this, or something like that.  */
 314     int op_size;
 315
 316     /* The size of the data operated upon, in bits, for bytecodes that
 317        care about that (ref and const).  Zero for all others.  */
 318     int data_size;
 319
 320     /* Number of stack elements consumed, and number produced.  */
 321     int consumed, produced;
 322   };
 323
 324 /* Map of the bytecodes, indexed by bytecode number.  */
 325
 326 static struct aop_map aop_map[] =
 327 {
 328   {0, 0, 0, 0, 0}
 329 #define DEFOP(NAME, SIZE, DATA_SIZE, CONSUMED, PRODUCED, VALUE) \
 330   , { # NAME, SIZE, DATA_SIZE, CONSUMED, PRODUCED }
 331 #include "gdbsupport/ax.def"
 332 #undef DEFOP
 333 };
 334
 335
 336 /* Disassemble the expression EXPR, writing to F.  */
 337 void
 338 ax_print (struct ui_file *f, struct agent_expr *x)
 339 {
 340   int i;
 341
 342   gdb_printf (f, _("Scope: %s\n"), paddress (x->gdbarch, x->scope));
 343   gdb_printf (f, _("Reg mask:"));
 344   for (i = 0; i < x->reg_mask.size (); ++i)
 345     {
 346       if ((i % 8) == 0)
 347         gdb_printf (f, " ");
 348       gdb_printf (f, _("%d"), (int) x->reg_mask[i]);
 349     }
 350   gdb_printf (f, _("\n"));
 351
 352   for (i = 0; i < x->buf.size ();)
 353     {
 354       enum agent_op op = (enum agent_op) x->buf[i];
 355
 356       if (op >= ARRAY_SIZE (aop_map) || aop_map[op].name == nullptr)
 357         {
 358           gdb_printf (f, _("%3d  <bad opcode %02x>\n"), i, op);
 359           i++;
 360           continue;
 361         }
 362       if (i + 1 + aop_map[op].op_size > x->buf.size ())
 363         {
 364           gdb_printf (f, _("%3d  <incomplete opcode %s>\n"),
 365                       i, aop_map[op].name);
 366           break;
 367         }
 368
 369       gdb_printf (f, "%3d  %s", i, aop_map[op].name);
 370       if (aop_map[op].op_size > 0)
 371         {
 372           gdb_puts (" ", f);
 373
 374           print_longest (f, 'd', 0,
 375                          read_const (x, i + 1, aop_map[op].op_size));
 376         }
 377       /* Handle the complicated printf arguments specially.  */
 378       else if (op == aop_printf)
 379         {
 380           int slen, nargs;
 381
 382           i++;
 383           nargs = x->buf[i++];
 384           slen = x->buf[i++];
 385           slen = slen * 256 + x->buf[i++];
 386           gdb_printf (f, _(" \"%s\", %d args"),
 387                       &(x->buf[i]), nargs);
 388           i += slen - 1;
 389         }
 390       gdb_printf (f, "\n");
 391       i += 1 + aop_map[op].op_size;
 392     }
 393 }
 394
 395 /* Add register REG to the register mask for expression AX.  */
 396 void
 397 ax_reg_mask (struct agent_expr *ax, int reg)
 398 {
 399   if (reg >= gdbarch_num_regs (ax->gdbarch))
 400     {
 401       /* This is a pseudo-register.  */
 402       if (!gdbarch_ax_pseudo_register_collect_p (ax->gdbarch))
 403         error (_("'%s' is a pseudo-register; "
 404                  "GDB cannot yet trace its contents."),
 405                user_reg_map_regnum_to_name (ax->gdbarch, reg));
 406       if (gdbarch_ax_pseudo_register_collect (ax->gdbarch, ax, reg))
 407         error (_("Trace '%s' failed."),
 408                user_reg_map_regnum_to_name (ax->gdbarch, reg));
 409     }
 410   else
 411     {
 412       /* Get the remote register number.  */
 413       reg = gdbarch_remote_register_number (ax->gdbarch, reg);
 414
 415       /* Grow the bit mask if necessary.  */
 416       if (reg >= ax->reg_mask.size ())
 417         ax->reg_mask.resize (reg + 1);
 418
 419       ax->reg_mask[reg] = true;
 420     }
 421 }
 422
 423 /* Given an agent expression AX, fill in requirements and other descriptive
 424    bits.  */
 425 void
 426 ax_reqs (struct agent_expr *ax)
 427 {
 428   int i;
 429   int height;
 430
 431   /* Jump target table.  targets[i] is non-zero iff we have found a
 432      jump to offset i.  */
 433   char *targets = (char *) alloca (ax->buf.size () * sizeof (targets[0]));
 434
 435   /* Instruction boundary table.  boundary[i] is non-zero iff our scan
 436      has reached an instruction starting at offset i.  */
 437   char *boundary = (char *) alloca (ax->buf.size () * sizeof (boundary[0]));
 438
 439   /* Stack height record.  If either targets[i] or boundary[i] is
 440      non-zero, heights[i] is the height the stack should have before
 441      executing the bytecode at that point.  */
 442   int *heights = (int *) alloca (ax->buf.size () * sizeof (heights[0]));
 443
 444   /* Pointer to a description of the present op.  */
 445   struct aop_map *op;
 446
 447   memset (targets, 0, ax->buf.size () * sizeof (targets[0]));
 448   memset (boundary, 0, ax->buf.size () * sizeof (boundary[0]));
 449
 450   ax->max_height = ax->min_height = height = 0;
 451   ax->flaw = agent_flaw_none;
 452   ax->max_data_size = 0;
 453
 454   for (i = 0; i < ax->buf.size (); i += 1 + op->op_size)
 455     {
 456       if (ax->buf[i] >= ARRAY_SIZE (aop_map))
 457         {
 458           ax->flaw = agent_flaw_bad_instruction;
 459           return;
 460         }
 461
 462       op = &aop_map[ax->buf[i]];
 463
 464       if (!op->name)
 465         {
 466           ax->flaw = agent_flaw_bad_instruction;
 467           return;
 468         }
 469
 470       if (i + 1 + op->op_size > ax->buf.size ())
 471         {
 472           ax->flaw = agent_flaw_incomplete_instruction;
 473           return;
 474         }
 475
 476       /* If this instruction is a forward jump target, does the
 477          current stack height match the stack height at the jump
 478          source?  */
 479       if (targets[i] && (heights[i] != height))
 480         {
 481           ax->flaw = agent_flaw_height_mismatch;
 482           return;
 483         }
 484
 485       boundary[i] = 1;
 486       heights[i] = height;
 487
 488       height -= op->consumed;
 489       if (height < ax->min_height)
 490         ax->min_height = height;
 491       height += op->produced;
 492       if (height > ax->max_height)
 493         ax->max_height = height;
 494
 495       if (op->data_size > ax->max_data_size)
 496         ax->max_data_size = op->data_size;
 497
 498       /* For jump instructions, check that the target is a valid
 499          offset.  If it is, record the fact that that location is a
 500          jump target, and record the height we expect there.  */
 501       if (aop_goto == op - aop_map
 502           || aop_if_goto == op - aop_map)
 503         {
 504           int target = read_const (ax, i + 1, 2);
 505           if (target < 0 || target >= ax->buf.size ())
 506             {
 507               ax->flaw = agent_flaw_bad_jump;
 508               return;
 509             }
 510
 511           /* Do we have any information about what the stack height
 512              should be at the target?  */
 513           if (targets[target] || boundary[target])
 514             {
 515               if (heights[target] != height)
 516                 {
 517                   ax->flaw = agent_flaw_height_mismatch;
 518                   return;
 519                 }
 520             }
 521
 522           /* Record the target, along with the stack height we expect.  */
 523           targets[target] = 1;
 524           heights[target] = height;
 525         }
 526
 527       /* For unconditional jumps with a successor, check that the
 528          successor is a target, and pick up its stack height.  */
 529       if (aop_goto == op - aop_map
 530           && i + 3 < ax->buf.size ())
 531         {
 532           if (!targets[i + 3])
 533             {
 534               ax->flaw = agent_flaw_hole;
 535               return;
 536             }
 537
 538           height = heights[i + 3];
 539         }
 540
 541       /* For reg instructions, record the register in the bit mask.  */
 542       if (aop_reg == op - aop_map)
 543         {
 544           int reg = read_const (ax, i + 1, 2);
 545
 546           ax_reg_mask (ax, reg);
 547         }
 548     }
 549
 550   /* Check that all the targets are on boundaries.  */
 551   for (i = 0; i < ax->buf.size (); i++)
 552     if (targets[i] && !boundary[i])
 553       {
 554         ax->flaw = agent_flaw_bad_jump;
 555         return;
 556       }
 557
 558   ax->final_height = height;
 559 }