gdb/ax.h

   1 /* Definitions for expressions designed to be executed on the agent
   2    Copyright (C) 1998-2019 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 AX_H
  20 #define AX_H
  21
  22 #include "common/vec.h"
  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 /* A buffer containing a agent expression.  */
  83 struct agent_expr
  84   {
  85     /* Construct an empty agent expression.  */
  86     explicit agent_expr (struct gdbarch *gdbarch, CORE_ADDR scope);
  87
  88     ~agent_expr ();
  89
  90     /* The bytes of the expression.  */
  91     unsigned char *buf;
  92
  93     /* The number of bytecode in the expression.  */
  94     int len;
  95
  96     /* Allocated space available currently.  */
  97     int size;
  98
  99     /* The target architecture assumed to be in effect.  */
 100     struct gdbarch *gdbarch;
 101
 102     /* The address to which the expression applies.  */
 103     CORE_ADDR scope;
 104
 105     /* If the following is not equal to agent_flaw_none, the rest of the
 106        information in this structure is suspect.  */
 107     enum agent_flaws flaw;
 108
 109     /* Number of elements left on stack at end; may be negative if expr
 110        only consumes elements.  */
 111     int final_height;
 112
 113     /* Maximum and minimum stack height, relative to initial height.  */
 114     int max_height, min_height;
 115
 116     /* Largest `ref' or `const' opcode used, in bits.  Zero means the
 117        expression has no such instructions.  */
 118     int max_data_size;
 119
 120     /* Bit vector of registers needed.  Register R is needed iff
 121
 122        reg_mask[R / 8] & (1 << (R % 8))
 123
 124        is non-zero.  Note!  You may not assume that this bitmask is long
 125        enough to hold bits for all the registers of the machine; the
 126        agent expression code has no idea how many registers the machine
 127        has.  However, the bitmask is reg_mask_len bytes long, so the
 128        valid register numbers run from 0 to reg_mask_len * 8 - 1.
 129
 130        Also note that this mask may contain registers that are needed
 131        for the original collection expression to work, but that are
 132        not referenced by any bytecode.  This could, for example, occur
 133        when collecting a local variable allocated to a register; the
 134        compiler sets the mask bit and skips generating a bytecode whose
 135        result is going to be discarded anyway.
 136     */
 137     int reg_mask_len;
 138     unsigned char *reg_mask;
 139
 140     /* For the data tracing facility, we need to insert `trace' bytecodes
 141        before each data fetch; this records all the memory that the
 142        expression touches in the course of evaluation, so that memory will
 143        be available when the user later tries to evaluate the expression
 144        in GDB.
 145
 146        Setting the flag 'tracing' to non-zero enables the code that
 147        emits the trace bytecodes at the appropriate points.  */
 148
 149     unsigned int tracing : 1;
 150
 151     /* This indicates that pointers to chars should get an added
 152        tracenz bytecode to record nonzero bytes, up to a length that
 153        is the value of trace_string.  */
 154
 155     int trace_string;
 156   };
 157
 158 /* An agent_expr owning pointer.  */
 159 typedef std::unique_ptr<agent_expr> agent_expr_up;
 160
 161 /* The actual values of the various bytecode operations.  */
 162
 163 enum agent_op
 164   {
 165 #define DEFOP(NAME, SIZE, DATA_SIZE, CONSUMED, PRODUCED, VALUE)  \
 166     aop_ ## NAME = VALUE,
 167 #include "common/ax.def"
 168 #undef DEFOP
 169     aop_last
 170   };
 171 \f
 172
 173
 174 /* Functions for building expressions.  */
 175
 176 /* Append a raw byte to EXPR.  */
 177 extern void ax_raw_byte (struct agent_expr *expr, gdb_byte byte);
 178
 179 /* Append a simple operator OP to EXPR.  */
 180 extern void ax_simple (struct agent_expr *EXPR, enum agent_op OP);
 181
 182 /* Append a pick operator to EXPR.  DEPTH is the stack item to pick,
 183    with 0 being top of stack.  */
 184 extern void ax_pick (struct agent_expr *EXPR, int DEPTH);
 185
 186 /* Append the floating-point prefix, for the next bytecode.  */
 187 #define ax_float(EXPR) (ax_simple ((EXPR), aop_float))
 188
 189 /* Append a sign-extension instruction to EXPR, to extend an N-bit value.  */
 190 extern void ax_ext (struct agent_expr *EXPR, int N);
 191
 192 /* Append a zero-extension instruction to EXPR, to extend an N-bit value.  */
 193 extern void ax_zero_ext (struct agent_expr *EXPR, int N);
 194
 195 /* Append a trace_quick instruction to EXPR, to record N bytes.  */
 196 extern void ax_trace_quick (struct agent_expr *EXPR, int N);
 197
 198 /* Append a goto op to EXPR.  OP is the actual op (must be aop_goto or
 199    aop_if_goto).  We assume we don't know the target offset yet,
 200    because it's probably a forward branch, so we leave space in EXPR
 201    for the target, and return the offset in EXPR of that space, so we
 202    can backpatch it once we do know the target offset.  Use ax_label
 203    to do the backpatching.  */
 204 extern int ax_goto (struct agent_expr *EXPR, enum agent_op OP);
 205
 206 /* Suppose a given call to ax_goto returns some value PATCH.  When you
 207    know the offset TARGET that goto should jump to, call
 208    ax_label (EXPR, PATCH, TARGET)
 209    to patch TARGET into the ax_goto instruction.  */
 210 extern void ax_label (struct agent_expr *EXPR, int patch, int target);
 211
 212 /* Assemble code to push a constant on the stack.  */
 213 extern void ax_const_l (struct agent_expr *EXPR, LONGEST l);
 214 extern void ax_const_d (struct agent_expr *EXPR, LONGEST d);
 215
 216 /* Assemble code to push the value of register number REG on the
 217    stack.  */
 218 extern void ax_reg (struct agent_expr *EXPR, int REG);
 219
 220 /* Add the given register to the register mask of the expression.  */
 221 extern void ax_reg_mask (struct agent_expr *ax, int reg);
 222
 223 /* Assemble code to operate on a trace state variable.  */
 224 extern void ax_tsv (struct agent_expr *expr, enum agent_op op, int num);
 225
 226 /* Append a string to the bytecode stream.  */
 227 extern void ax_string (struct agent_expr *x, const char *str, int slen);
 228 \f
 229
 230 /* Functions for printing out expressions, and otherwise debugging
 231    things.  */
 232
 233 /* Disassemble the expression EXPR, writing to F.  */
 234 extern void ax_print (struct ui_file *f, struct agent_expr * EXPR);
 235
 236 /* An entry in the opcode map.  */
 237 struct aop_map
 238   {
 239
 240     /* The name of the opcode.  Null means that this entry is not a
 241        valid opcode --- a hole in the opcode space.  */
 242     const char *name;
 243
 244     /* All opcodes take no operands from the bytecode stream, or take
 245        unsigned integers of various sizes.  If this is a positive number
 246        n, then the opcode is followed by an n-byte operand, which should
 247        be printed as an unsigned integer.  If this is zero, then the
 248        opcode takes no operands from the bytecode stream.
 249
 250        If we get more complicated opcodes in the future, don't add other
 251        magic values of this; that's a crock.  Add an `enum encoding'
 252        field to this, or something like that.  */
 253     int op_size;
 254
 255     /* The size of the data operated upon, in bits, for bytecodes that
 256        care about that (ref and const).  Zero for all others.  */
 257     int data_size;
 258
 259     /* Number of stack elements consumed, and number produced.  */
 260     int consumed, produced;
 261   };
 262
 263 /* Map of the bytecodes, indexed by bytecode number.  */
 264 extern struct aop_map aop_map[];
 265
 266 /* Given an agent expression AX, analyze and update its requirements.  */
 267
 268 extern void ax_reqs (struct agent_expr *ax);
 269
 270 #endif /* AX_H */