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