gdb/ax.h

   1 /* Definitions for expressions designed to be executed on the agent
   2    Copyright (C) 1998-2016 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 #include "vec.h"
  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 /* Different kinds of flaws an agent expression might have, as
  55    detected by ax_reqs.  */
  56 enum agent_flaws
  57   {
  58     agent_flaw_none = 0,        /* code is good */
  59
  60     /* There is an invalid instruction in the stream.  */
  61     agent_flaw_bad_instruction,
  62
  63     /* There is an incomplete instruction at the end of the expression.  */
  64     agent_flaw_incomplete_instruction,
  65
  66     /* ax_reqs was unable to prove that every jump target is to a
  67        valid offset.  Valid offsets are within the bounds of the
  68        expression, and to a valid instruction boundary.  */
  69     agent_flaw_bad_jump,
  70
  71     /* ax_reqs was unable to prove to its satisfaction that, for each
  72        jump target location, the stack will have the same height whether
  73        that location is reached via a jump or by straight execution.  */
  74     agent_flaw_height_mismatch,
  75
  76     /* ax_reqs was unable to prove that every instruction following
  77        an unconditional jump was the target of some other jump.  */
  78     agent_flaw_hole
  79   };
  80
  81 /* Agent expression data structures.  */
  82
  83 /* The type of an element of the agent expression stack.
  84    The bytecode operation indicates which element we should access;
  85    the value itself has no typing information.  GDB generates all
  86    bytecode streams, so we don't have to worry about type errors.  */
  87
  88 union agent_val
  89   {
  90     LONGEST l;
  91     DOUBLEST d;
  92   };
  93
  94 /* A buffer containing a agent expression.  */
  95 struct agent_expr
  96   {
  97     /* The bytes of the expression.  */
  98     unsigned char *buf;
  99
 100     /* The number of bytecode in the expression.  */
 101     int len;
 102
 103     /* Allocated space available currently.  */
 104     int size;
 105
 106     /* The target architecture assumed to be in effect.  */
 107     struct gdbarch *gdbarch;
 108
 109     /* The address to which the expression applies.  */
 110     CORE_ADDR scope;
 111
 112     /* If the following is not equal to agent_flaw_none, the rest of the
 113        information in this structure is suspect.  */
 114     enum agent_flaws flaw;
 115
 116     /* Number of elements left on stack at end; may be negative if expr
 117        only consumes elements.  */
 118     int final_height;
 119
 120     /* Maximum and minimum stack height, relative to initial height.  */
 121     int max_height, min_height;
 122
 123     /* Largest `ref' or `const' opcode used, in bits.  Zero means the
 124        expression has no such instructions.  */
 125     int max_data_size;
 126
 127     /* Bit vector of registers needed.  Register R is needed iff
 128
 129        reg_mask[R / 8] & (1 << (R % 8))
 130
 131        is non-zero.  Note!  You may not assume that this bitmask is long
 132        enough to hold bits for all the registers of the machine; the
 133        agent expression code has no idea how many registers the machine
 134        has.  However, the bitmask is reg_mask_len bytes long, so the
 135        valid register numbers run from 0 to reg_mask_len * 8 - 1.
 136
 137        Also note that this mask may contain registers that are needed
 138        for the original collection expression to work, but that are
 139        not referenced by any bytecode.  This could, for example, occur
 140        when collecting a local variable allocated to a register; the
 141        compiler sets the mask bit and skips generating a bytecode whose
 142        result is going to be discarded anyway.
 143     */
 144     int reg_mask_len;
 145     unsigned char *reg_mask;
 146
 147     /* For the data tracing facility, we need to insert `trace' bytecodes
 148        before each data fetch; this records all the memory that the
 149        expression touches in the course of evaluation, so that memory will
 150        be available when the user later tries to evaluate the expression
 151        in GDB.
 152
 153        Setting the flag 'tracing' to non-zero enables the code that
 154        emits the trace bytecodes at the appropriate points.  */
 155
 156     unsigned int tracing : 1;
 157
 158     /* This indicates that pointers to chars should get an added
 159        tracenz bytecode to record nonzero bytes, up to a length that
 160        is the value of trace_string.  */
 161
 162     int trace_string;
 163   };
 164
 165 /* Pointer to an agent_expr structure.  */
 166 typedef struct agent_expr *agent_expr_p;
 167
 168 /* Vector of pointers to agent expressions.  */
 169 DEF_VEC_P (agent_expr_p);
 170
 171 /* The actual values of the various bytecode operations.  */
 172
 173 enum agent_op
 174   {
 175 #define DEFOP(NAME, SIZE, DATA_SIZE, CONSUMED, PRODUCED, VALUE)  \
 176     aop_ ## NAME = VALUE,
 177 #include "ax.def"
 178 #undef DEFOP
 179     aop_last
 180   };
 181 \f
 182
 183
 184 /* Functions for building expressions.  */
 185
 186 /* Allocate a new, empty agent expression.  */
 187 extern struct agent_expr *new_agent_expr (struct gdbarch *, CORE_ADDR);
 188
 189 /* Free a agent expression.  */
 190 extern void free_agent_expr (struct agent_expr *);
 191 extern struct cleanup *make_cleanup_free_agent_expr (struct agent_expr *);
 192
 193 /* Append a raw byte to EXPR.  */
 194 extern void ax_raw_byte (struct agent_expr *expr, gdb_byte byte);
 195
 196 /* Append a simple operator OP to EXPR.  */
 197 extern void ax_simple (struct agent_expr *EXPR, enum agent_op OP);
 198
 199 /* Append a pick operator to EXPR.  DEPTH is the stack item to pick,
 200    with 0 being top of stack.  */
 201 extern void ax_pick (struct agent_expr *EXPR, int DEPTH);
 202
 203 /* Append the floating-point prefix, for the next bytecode.  */
 204 #define ax_float(EXPR) (ax_simple ((EXPR), aop_float))
 205
 206 /* Append a sign-extension instruction to EXPR, to extend an N-bit value.  */
 207 extern void ax_ext (struct agent_expr *EXPR, int N);
 208
 209 /* Append a zero-extension instruction to EXPR, to extend an N-bit value.  */
 210 extern void ax_zero_ext (struct agent_expr *EXPR, int N);
 211
 212 /* Append a trace_quick instruction to EXPR, to record N bytes.  */
 213 extern void ax_trace_quick (struct agent_expr *EXPR, int N);
 214
 215 /* Append a goto op to EXPR.  OP is the actual op (must be aop_goto or
 216    aop_if_goto).  We assume we don't know the target offset yet,
 217    because it's probably a forward branch, so we leave space in EXPR
 218    for the target, and return the offset in EXPR of that space, so we
 219    can backpatch it once we do know the target offset.  Use ax_label
 220    to do the backpatching.  */
 221 extern int ax_goto (struct agent_expr *EXPR, enum agent_op OP);
 222
 223 /* Suppose a given call to ax_goto returns some value PATCH.  When you
 224    know the offset TARGET that goto should jump to, call
 225    ax_label (EXPR, PATCH, TARGET)
 226    to patch TARGET into the ax_goto instruction.  */
 227 extern void ax_label (struct agent_expr *EXPR, int patch, int target);
 228
 229 /* Assemble code to push a constant on the stack.  */
 230 extern void ax_const_l (struct agent_expr *EXPR, LONGEST l);
 231 extern void ax_const_d (struct agent_expr *EXPR, LONGEST d);
 232
 233 /* Assemble code to push the value of register number REG on the
 234    stack.  */
 235 extern void ax_reg (struct agent_expr *EXPR, int REG);
 236
 237 /* Add the given register to the register mask of the expression.  */
 238 extern void ax_reg_mask (struct agent_expr *ax, int reg);
 239
 240 /* Assemble code to operate on a trace state variable.  */
 241 extern void ax_tsv (struct agent_expr *expr, enum agent_op op, int num);
 242
 243 /* Append a string to the bytecode stream.  */
 244 extern void ax_string (struct agent_expr *x, const char *str, int slen);
 245 \f
 246
 247 /* Functions for printing out expressions, and otherwise debugging
 248    things.  */
 249
 250 /* Disassemble the expression EXPR, writing to F.  */
 251 extern void ax_print (struct ui_file *f, struct agent_expr * EXPR);
 252
 253 /* An entry in the opcode map.  */
 254 struct aop_map
 255   {
 256
 257     /* The name of the opcode.  Null means that this entry is not a
 258        valid opcode --- a hole in the opcode space.  */
 259     const char *name;
 260
 261     /* All opcodes take no operands from the bytecode stream, or take
 262        unsigned integers of various sizes.  If this is a positive number
 263        n, then the opcode is followed by an n-byte operand, which should
 264        be printed as an unsigned integer.  If this is zero, then the
 265        opcode takes no operands from the bytecode stream.
 266
 267        If we get more complicated opcodes in the future, don't add other
 268        magic values of this; that's a crock.  Add an `enum encoding'
 269        field to this, or something like that.  */
 270     int op_size;
 271
 272     /* The size of the data operated upon, in bits, for bytecodes that
 273        care about that (ref and const).  Zero for all others.  */
 274     int data_size;
 275
 276     /* Number of stack elements consumed, and number produced.  */
 277     int consumed, produced;
 278   };
 279
 280 /* Map of the bytecodes, indexed by bytecode number.  */
 281 extern struct aop_map aop_map[];
 282
 283 /* Given an agent expression AX, analyze and update its requirements.  */
 284
 285 extern void ax_reqs (struct agent_expr *ax);
 286
 287 #endif /* AGENTEXPR_H */