gdb/ax.h

   1 /* Definitions for expressions designed to be executed on the agent
   2    Copyright (C) 1998-2000, 2007-2012 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 #ifndef AGENTEXPR_H
  20 #define AGENTEXPR_H
  21
  22 #include "doublest.h"           /* For DOUBLEST.  */
  23
  24 /* It's sometimes useful to be able to debug programs that you can't
  25    really stop for more than a fraction of a second.  To this end, the
  26    user can specify a tracepoint (like a breakpoint, but you don't
  27    stop at it), and specify a bunch of expressions to record the
  28    values of when that tracepoint is reached.  As the program runs,
  29    GDB collects the values.  At any point (possibly while values are
  30    still being collected), the user can display the collected values.
  31
  32    This is used with remote debugging; we don't really support it on
  33    native configurations.
  34
  35    This means that expressions are being evaluated by the remote agent,
  36    which doesn't have any access to the symbol table information, and
  37    needs to be small and simple.
  38
  39    The agent_expr routines and datatypes are a bytecode language
  40    designed to be executed by the agent.  Agent expressions work in
  41    terms of fixed-width values, operators, memory references, and
  42    register references.  You can evaluate a agent expression just given
  43    a bunch of memory and register values to sniff at; you don't need
  44    any symbolic information like variable names, types, etc.
  45
  46    GDB translates source expressions, whose meaning depends on
  47    symbolic information, into agent bytecode expressions, whose meaning
  48    is independent of symbolic information.  This means the agent can
  49    evaluate them on the fly without reference to data only available
  50    to the host GDB.  */
  51 \f
  52
  53 /* Different kinds of flaws an agent expression might have, as
  54    detected by ax_reqs.  */
  55 enum agent_flaws
  56   {
  57     agent_flaw_none = 0,        /* code is good */
  58
  59     /* There is an invalid instruction in the stream.  */
  60     agent_flaw_bad_instruction,
  61
  62     /* There is an incomplete instruction at the end of the expression.  */
  63     agent_flaw_incomplete_instruction,
  64
  65     /* ax_reqs was unable to prove that every jump target is to a
  66        valid offset.  Valid offsets are within the bounds of the
  67        expression, and to a valid instruction boundary.  */
  68     agent_flaw_bad_jump,
  69
  70     /* ax_reqs was unable to prove to its satisfaction that, for each
  71        jump target location, the stack will have the same height whether
  72        that location is reached via a jump or by straight execution.  */
  73     agent_flaw_height_mismatch,
  74
  75     /* ax_reqs was unable to prove that every instruction following
  76        an unconditional jump was the target of some other jump.  */
  77     agent_flaw_hole
  78   };
  79
  80 /* Agent expression data structures.  */
  81
  82 /* The type of an element of the agent expression stack.
  83    The bytecode operation indicates which element we should access;
  84    the value itself has no typing information.  GDB generates all
  85    bytecode streams, so we don't have to worry about type errors.  */
  86
  87 union agent_val
  88   {
  89     LONGEST l;
  90     DOUBLEST d;
  91   };
  92
  93 /* A buffer containing a agent expression.  */
  94 struct agent_expr
  95   {
  96     /* The bytes of the expression.  */
  97     unsigned char *buf;
  98
  99     /* The number of bytecode in the expression.  */
 100     int len;
 101
 102     /* Allocated space available currently.  */
 103     int size;
 104
 105     /* The target architecture assumed to be in effect.  */
 106     struct gdbarch *gdbarch;
 107
 108     /* The address to which the expression applies.  */
 109     CORE_ADDR scope;
 110
 111     /* If the following is not equal to agent_flaw_none, the rest of the
 112        information in this structure is suspect.  */
 113     enum agent_flaws flaw;
 114
 115     /* Number of elements left on stack at end; may be negative if expr
 116        only consumes elements.  */
 117     int final_height;
 118
 119     /* Maximum and minimum stack height, relative to initial height.  */
 120     int max_height, min_height;
 121
 122     /* Largest `ref' or `const' opcode used, in bits.  Zero means the
 123        expression has no such instructions.  */
 124     int max_data_size;
 125
 126     /* Bit vector of registers needed.  Register R is needed iff
 127
 128        reg_mask[R / 8] & (1 << (R % 8))
 129
 130        is non-zero.  Note!  You may not assume that this bitmask is long
 131        enough to hold bits for all the registers of the machine; the
 132        agent expression code has no idea how many registers the machine
 133        has.  However, the bitmask is reg_mask_len bytes long, so the
 134        valid register numbers run from 0 to reg_mask_len * 8 - 1.
 135
 136        Also note that this mask may contain registers that are needed
 137        for the original collection expression to work, but that are
 138        not referenced by any bytecode.  This could, for example, occur
 139        when collecting a local variable allocated to a register; the
 140        compiler sets the mask bit and skips generating a bytecode whose
 141        result is going to be discarded anyway.
 142     */
 143     int reg_mask_len;
 144     unsigned char *reg_mask;
 145   };
 146
 147 /* The actual values of the various bytecode operations.  */
 148
 149 enum agent_op
 150   {
 151 #define DEFOP(NAME, SIZE, DATA_SIZE, CONSUMED, PRODUCED, VALUE)  \
 152     aop_ ## NAME = VALUE,
 153 #include "ax.def"
 154 #undef DEFOP
 155     aop_last
 156   };
 157 \f
 158
 159
 160 /* Functions for building expressions.  */
 161
 162 /* Allocate a new, empty agent expression.  */
 163 extern struct agent_expr *new_agent_expr (struct gdbarch *, CORE_ADDR);
 164
 165 /* Free a agent expression.  */
 166 extern void free_agent_expr (struct agent_expr *);
 167 extern struct cleanup *make_cleanup_free_agent_expr (struct agent_expr *);
 168
 169 /* Append a simple operator OP to EXPR.  */
 170 extern void ax_simple (struct agent_expr *EXPR, enum agent_op OP);
 171
 172 /* Append a pick operator to EXPR.  DEPTH is the stack item to pick,
 173    with 0 being top of stack.  */
 174 extern void ax_pick (struct agent_expr *EXPR, int DEPTH);
 175
 176 /* Append the floating-point prefix, for the next bytecode.  */
 177 #define ax_float(EXPR) (ax_simple ((EXPR), aop_float))
 178
 179 /* Append a sign-extension instruction to EXPR, to extend an N-bit value.  */
 180 extern void ax_ext (struct agent_expr *EXPR, int N);
 181
 182 /* Append a zero-extension instruction to EXPR, to extend an N-bit value.  */
 183 extern void ax_zero_ext (struct agent_expr *EXPR, int N);
 184
 185 /* Append a trace_quick instruction to EXPR, to record N bytes.  */
 186 extern void ax_trace_quick (struct agent_expr *EXPR, int N);
 187
 188 /* Append a goto op to EXPR.  OP is the actual op (must be aop_goto or
 189    aop_if_goto).  We assume we don't know the target offset yet,
 190    because it's probably a forward branch, so we leave space in EXPR
 191    for the target, and return the offset in EXPR of that space, so we
 192    can backpatch it once we do know the target offset.  Use ax_label
 193    to do the backpatching.  */
 194 extern int ax_goto (struct agent_expr *EXPR, enum agent_op OP);
 195
 196 /* Suppose a given call to ax_goto returns some value PATCH.  When you
 197    know the offset TARGET that goto should jump to, call
 198    ax_label (EXPR, PATCH, TARGET)
 199    to patch TARGET into the ax_goto instruction.  */
 200 extern void ax_label (struct agent_expr *EXPR, int patch, int target);
 201
 202 /* Assemble code to push a constant on the stack.  */
 203 extern void ax_const_l (struct agent_expr *EXPR, LONGEST l);
 204 extern void ax_const_d (struct agent_expr *EXPR, LONGEST d);
 205
 206 /* Assemble code to push the value of register number REG on the
 207    stack.  */
 208 extern void ax_reg (struct agent_expr *EXPR, int REG);
 209
 210 /* Add the given register to the register mask of the expression.  */
 211 extern void ax_reg_mask (struct agent_expr *ax, int reg);
 212
 213 /* Assemble code to operate on a trace state variable.  */
 214 extern void ax_tsv (struct agent_expr *expr, enum agent_op op, int num);
 215 \f
 216
 217 /* Functions for printing out expressions, and otherwise debugging
 218    things.  */
 219
 220 /* Disassemble the expression EXPR, writing to F.  */
 221 extern void ax_print (struct ui_file *f, struct agent_expr * EXPR);
 222
 223 /* An entry in the opcode map.  */
 224 struct aop_map
 225   {
 226
 227     /* The name of the opcode.  Null means that this entry is not a
 228        valid opcode --- a hole in the opcode space.  */
 229     const char *name;
 230
 231     /* All opcodes take no operands from the bytecode stream, or take
 232        unsigned integers of various sizes.  If this is a positive number
 233        n, then the opcode is followed by an n-byte operand, which should
 234        be printed as an unsigned integer.  If this is zero, then the
 235        opcode takes no operands from the bytecode stream.
 236
 237        If we get more complicated opcodes in the future, don't add other
 238        magic values of this; that's a crock.  Add an `enum encoding'
 239        field to this, or something like that.  */
 240     int op_size;
 241
 242     /* The size of the data operated upon, in bits, for bytecodes that
 243        care about that (ref and const).  Zero for all others.  */
 244     int data_size;
 245
 246     /* Number of stack elements consumed, and number produced.  */
 247     int consumed, produced;
 248   };
 249
 250 /* Map of the bytecodes, indexed by bytecode number.  */
 251 extern struct aop_map aop_map[];
 252
 253 /* Given an agent expression AX, analyze and update its requirements.  */
 254
 255 extern void ax_reqs (struct agent_expr *ax);
 256
 257 #endif /* AGENTEXPR_H */