gdb/ax.h

   1 /* Definitions for expressions designed to be executed on the agent
   2    Copyright (C) 1998, 1999, 2000, 2007, 2008, 2009
   3    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 #ifndef AGENTEXPR_H
  21 #define AGENTEXPR_H
  22
  23 #include "doublest.h"           /* For DOUBLEST.  */
  24
  25 /* It's sometimes useful to be able to debug programs that you can't
  26    really stop for more than a fraction of a second.  To this end, the
  27    user can specify a tracepoint (like a breakpoint, but you don't
  28    stop at it), and specify a bunch of expressions to record the
  29    values of when that tracepoint is reached.  As the program runs,
  30    GDB collects the values.  At any point (possibly while values are
  31    still being collected), the user can display the collected values.
  32
  33    This is used with remote debugging; we don't really support it on
  34    native configurations.
  35
  36    This means that expressions are being evaluated by the remote agent,
  37    which doesn't have any access to the symbol table information, and
  38    needs to be small and simple.
  39
  40    The agent_expr routines and datatypes are a bytecode language
  41    designed to be executed by the agent.  Agent expressions work in
  42    terms of fixed-width values, operators, memory references, and
  43    register references.  You can evaluate a agent expression just given
  44    a bunch of memory and register values to sniff at; you don't need
  45    any symbolic information like variable names, types, etc.
  46
  47    GDB translates source expressions, whose meaning depends on
  48    symbolic information, into agent bytecode expressions, whose meaning
  49    is independent of symbolic information.  This means the agent can
  50    evaluate them on the fly without reference to data only available
  51    to the host GDB.  */
  52 \f
  53
  54 /* Agent expression data structures.  */
  55
  56 /* The type of an element of the agent expression stack.
  57    The bytecode operation indicates which element we should access;
  58    the value itself has no typing information.  GDB generates all
  59    bytecode streams, so we don't have to worry about type errors.  */
  60
  61 union agent_val
  62   {
  63     LONGEST l;
  64     DOUBLEST d;
  65   };
  66
  67 /* A buffer containing a agent expression.  */
  68 struct agent_expr
  69   {
  70     unsigned char *buf;
  71     int len;                    /* number of characters used */
  72     int size;                   /* allocated size */
  73     CORE_ADDR scope;
  74   };
  75
  76
  77
  78
  79 /* The actual values of the various bytecode operations.
  80
  81    Other independent implementations of the agent bytecode engine will
  82    rely on the exact values of these enums, and may not be recompiled
  83    when we change this table.  The numeric values should remain fixed
  84    whenever possible.  Thus, we assign them values explicitly here (to
  85    allow gaps to form safely), and the disassembly table in
  86    agentexpr.h behaves like an opcode map.  If you want to see them
  87    grouped logically, see doc/agentexpr.texi.  */
  88
  89 enum agent_op
  90   {
  91     aop_float = 0x01,
  92     aop_add = 0x02,
  93     aop_sub = 0x03,
  94     aop_mul = 0x04,
  95     aop_div_signed = 0x05,
  96     aop_div_unsigned = 0x06,
  97     aop_rem_signed = 0x07,
  98     aop_rem_unsigned = 0x08,
  99     aop_lsh = 0x09,
 100     aop_rsh_signed = 0x0a,
 101     aop_rsh_unsigned = 0x0b,
 102     aop_trace = 0x0c,
 103     aop_trace_quick = 0x0d,
 104     aop_log_not = 0x0e,
 105     aop_bit_and = 0x0f,
 106     aop_bit_or = 0x10,
 107     aop_bit_xor = 0x11,
 108     aop_bit_not = 0x12,
 109     aop_equal = 0x13,
 110     aop_less_signed = 0x14,
 111     aop_less_unsigned = 0x15,
 112     aop_ext = 0x16,
 113     aop_ref8 = 0x17,
 114     aop_ref16 = 0x18,
 115     aop_ref32 = 0x19,
 116     aop_ref64 = 0x1a,
 117     aop_ref_float = 0x1b,
 118     aop_ref_double = 0x1c,
 119     aop_ref_long_double = 0x1d,
 120     aop_l_to_d = 0x1e,
 121     aop_d_to_l = 0x1f,
 122     aop_if_goto = 0x20,
 123     aop_goto = 0x21,
 124     aop_const8 = 0x22,
 125     aop_const16 = 0x23,
 126     aop_const32 = 0x24,
 127     aop_const64 = 0x25,
 128     aop_reg = 0x26,
 129     aop_end = 0x27,
 130     aop_dup = 0x28,
 131     aop_pop = 0x29,
 132     aop_zero_ext = 0x2a,
 133     aop_swap = 0x2b,
 134     aop_trace16 = 0x30,
 135     aop_last
 136   };
 137 \f
 138
 139
 140 /* Functions for building expressions.  */
 141
 142 /* Allocate a new, empty agent expression.  */
 143 extern struct agent_expr *new_agent_expr (CORE_ADDR);
 144
 145 /* Free a agent expression.  */
 146 extern void free_agent_expr (struct agent_expr *);
 147 extern struct cleanup *make_cleanup_free_agent_expr (struct agent_expr *);
 148
 149 /* Append a simple operator OP to EXPR.  */
 150 extern void ax_simple (struct agent_expr *EXPR, enum agent_op OP);
 151
 152 /* Append the floating-point prefix, for the next bytecode.  */
 153 #define ax_float(EXPR) (ax_simple ((EXPR), aop_float))
 154
 155 /* Append a sign-extension instruction to EXPR, to extend an N-bit value.  */
 156 extern void ax_ext (struct agent_expr *EXPR, int N);
 157
 158 /* Append a zero-extension instruction to EXPR, to extend an N-bit value.  */
 159 extern void ax_zero_ext (struct agent_expr *EXPR, int N);
 160
 161 /* Append a trace_quick instruction to EXPR, to record N bytes.  */
 162 extern void ax_trace_quick (struct agent_expr *EXPR, int N);
 163
 164 /* Append a goto op to EXPR.  OP is the actual op (must be aop_goto or
 165    aop_if_goto).  We assume we don't know the target offset yet,
 166    because it's probably a forward branch, so we leave space in EXPR
 167    for the target, and return the offset in EXPR of that space, so we
 168    can backpatch it once we do know the target offset.  Use ax_label
 169    to do the backpatching.  */
 170 extern int ax_goto (struct agent_expr *EXPR, enum agent_op OP);
 171
 172 /* Suppose a given call to ax_goto returns some value PATCH.  When you
 173    know the offset TARGET that goto should jump to, call
 174    ax_label (EXPR, PATCH, TARGET)
 175    to patch TARGET into the ax_goto instruction.  */
 176 extern void ax_label (struct agent_expr *EXPR, int patch, int target);
 177
 178 /* Assemble code to push a constant on the stack.  */
 179 extern void ax_const_l (struct agent_expr *EXPR, LONGEST l);
 180 extern void ax_const_d (struct agent_expr *EXPR, LONGEST d);
 181
 182 /* Assemble code to push the value of register number REG on the
 183    stack.  */
 184 extern void ax_reg (struct agent_expr *EXPR, int REG);
 185 \f
 186
 187 /* Functions for printing out expressions, and otherwise debugging
 188    things.  */
 189
 190 /* Disassemble the expression EXPR, writing to F.  */
 191 extern void ax_print (struct ui_file *f, struct agent_expr * EXPR);
 192
 193 /* An entry in the opcode map.  */
 194 struct aop_map
 195   {
 196
 197     /* The name of the opcode.  Null means that this entry is not a
 198        valid opcode --- a hole in the opcode space.  */
 199     char *name;
 200
 201     /* All opcodes take no operands from the bytecode stream, or take
 202        unsigned integers of various sizes.  If this is a positive number
 203        n, then the opcode is followed by an n-byte operand, which should
 204        be printed as an unsigned integer.  If this is zero, then the
 205        opcode takes no operands from the bytecode stream.
 206
 207        If we get more complicated opcodes in the future, don't add other
 208        magic values of this; that's a crock.  Add an `enum encoding'
 209        field to this, or something like that.  */
 210     int op_size;
 211
 212     /* The size of the data operated upon, in bits, for bytecodes that
 213        care about that (ref and const).  Zero for all others.  */
 214     int data_size;
 215
 216     /* Number of stack elements consumed, and number produced.  */
 217     int consumed, produced;
 218   };
 219
 220 /* Map of the bytecodes, indexed by bytecode number.  */
 221 extern struct aop_map aop_map[];
 222
 223 /* Different kinds of flaws an agent expression might have, as
 224    detected by agent_reqs.  */
 225 enum agent_flaws
 226   {
 227     agent_flaw_none = 0,        /* code is good */
 228
 229     /* There is an invalid instruction in the stream.  */
 230     agent_flaw_bad_instruction,
 231
 232     /* There is an incomplete instruction at the end of the expression.  */
 233     agent_flaw_incomplete_instruction,
 234
 235     /* agent_reqs was unable to prove that every jump target is to a
 236        valid offset.  Valid offsets are within the bounds of the
 237        expression, and to a valid instruction boundary.  */
 238     agent_flaw_bad_jump,
 239
 240     /* agent_reqs was unable to prove to its satisfaction that, for each
 241        jump target location, the stack will have the same height whether
 242        that location is reached via a jump or by straight execution.  */
 243     agent_flaw_height_mismatch,
 244
 245     /* agent_reqs was unable to prove that every instruction following
 246        an unconditional jump was the target of some other jump.  */
 247     agent_flaw_hole
 248   };
 249
 250 /* Structure describing the requirements of a bytecode expression.  */
 251 struct agent_reqs
 252   {
 253
 254     /* If the following is not equal to agent_flaw_none, the rest of the
 255        information in this structure is suspect.  */
 256     enum agent_flaws flaw;
 257
 258     /* Number of elements left on stack at end; may be negative if expr
 259        only consumes elements.  */
 260     int final_height;
 261
 262     /* Maximum and minimum stack height, relative to initial height.  */
 263     int max_height, min_height;
 264
 265     /* Largest `ref' or `const' opcode used, in bits.  Zero means the
 266        expression has no such instructions.  */
 267     int max_data_size;
 268
 269     /* Bit vector of registers used.  Register R is used iff
 270
 271        reg_mask[R / 8] & (1 << (R % 8))
 272
 273        is non-zero.  Note!  You may not assume that this bitmask is long
 274        enough to hold bits for all the registers of the machine; the
 275        agent expression code has no idea how many registers the machine
 276        has.  However, the bitmask is reg_mask_len bytes long, so the
 277        valid register numbers run from 0 to reg_mask_len * 8 - 1.
 278
 279        We're assuming eight-bit bytes.  So sue me.
 280
 281        The caller should free reg_list when done.  */
 282     int reg_mask_len;
 283     unsigned char *reg_mask;
 284   };
 285
 286
 287 /* Given an agent expression AX, fill in an agent_reqs structure REQS
 288    describing it.  */
 289 extern void ax_reqs (struct agent_expr *ax, struct agent_reqs *reqs);
 290
 291 #endif /* AGENTEXPR_H */