gdb/ax.h

   1 /* Definitions for expressions designed to be executed on the agent
   2    Copyright (C) 1998-2020 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 /* It's sometimes useful to be able to debug programs that you can't
  23    really stop for more than a fraction of a second.  To this end, the
  24    user can specify a tracepoint (like a breakpoint, but you don't
  25    stop at it), and specify a bunch of expressions to record the
  26    values of when that tracepoint is reached.  As the program runs,
  27    GDB collects the values.  At any point (possibly while values are
  28    still being collected), the user can display the collected values.
  29
  30    This is used with remote debugging; we don't really support it on
  31    native configurations.
  32
  33    This means that expressions are being evaluated by the remote agent,
  34    which doesn't have any access to the symbol table information, and
  35    needs to be small and simple.
  36
  37    The agent_expr routines and datatypes are a bytecode language
  38    designed to be executed by the agent.  Agent expressions work in
  39    terms of fixed-width values, operators, memory references, and
  40    register references.  You can evaluate a agent expression just given
  41    a bunch of memory and register values to sniff at; you don't need
  42    any symbolic information like variable names, types, etc.
  43
  44    GDB translates source expressions, whose meaning depends on
  45    symbolic information, into agent bytecode expressions, whose meaning
  46    is independent of symbolic information.  This means the agent can
  47    evaluate them on the fly without reference to data only available
  48    to the host GDB.  */
  49 \f
  50
  51 /* Different kinds of flaws an agent expression might have, as
  52    detected by ax_reqs.  */
  53 enum agent_flaws
  54   {
  55     agent_flaw_none = 0,        /* code is good */
  56
  57     /* There is an invalid instruction in the stream.  */
  58     agent_flaw_bad_instruction,
  59
  60     /* There is an incomplete instruction at the end of the expression.  */
  61     agent_flaw_incomplete_instruction,
  62
  63     /* ax_reqs was unable to prove that every jump target is to a
  64        valid offset.  Valid offsets are within the bounds of the
  65        expression, and to a valid instruction boundary.  */
  66     agent_flaw_bad_jump,
  67
  68     /* ax_reqs was unable to prove to its satisfaction that, for each
  69        jump target location, the stack will have the same height whether
  70        that location is reached via a jump or by straight execution.  */
  71     agent_flaw_height_mismatch,
  72
  73     /* ax_reqs was unable to prove that every instruction following
  74        an unconditional jump was the target of some other jump.  */
  75     agent_flaw_hole
  76   };
  77
  78 /* Agent expression data structures.  */
  79
  80 /* A buffer containing a agent expression.  */
  81 struct agent_expr
  82   {
  83     /* Construct an empty agent expression.  */
  84     explicit agent_expr (struct gdbarch *gdbarch, CORE_ADDR scope);
  85
  86     ~agent_expr ();
  87
  88     /* The bytes of the expression.  */
  89     unsigned char *buf;
  90
  91     /* The number of bytecode in the expression.  */
  92     int len;
  93
  94     /* Allocated space available currently.  */
  95     int size;
  96
  97     /* The target architecture assumed to be in effect.  */
  98     struct gdbarch *gdbarch;
  99
 100     /* The address to which the expression applies.  */
 101     CORE_ADDR scope;
 102
 103     /* If the following is not equal to agent_flaw_none, the rest of the
 104        information in this structure is suspect.  */
 105     enum agent_flaws flaw;
 106
 107     /* Number of elements left on stack at end; may be negative if expr
 108        only consumes elements.  */
 109     int final_height;
 110
 111     /* Maximum and minimum stack height, relative to initial height.  */
 112     int max_height, min_height;
 113
 114     /* Largest `ref' or `const' opcode used, in bits.  Zero means the
 115        expression has no such instructions.  */
 116     int max_data_size;
 117
 118     /* Bit vector of registers needed.  Register R is needed iff
 119
 120        reg_mask[R / 8] & (1 << (R % 8))
 121
 122        is non-zero.  Note!  You may not assume that this bitmask is long
 123        enough to hold bits for all the registers of the machine; the
 124        agent expression code has no idea how many registers the machine
 125        has.  However, the bitmask is reg_mask_len bytes long, so the
 126        valid register numbers run from 0 to reg_mask_len * 8 - 1.
 127
 128        Also note that this mask may contain registers that are needed
 129        for the original collection expression to work, but that are
 130        not referenced by any bytecode.  This could, for example, occur
 131        when collecting a local variable allocated to a register; the
 132        compiler sets the mask bit and skips generating a bytecode whose
 133        result is going to be discarded anyway.
 134     */
 135     int reg_mask_len;
 136     unsigned char *reg_mask;
 137
 138     /* For the data tracing facility, we need to insert `trace' bytecodes
 139        before each data fetch; this records all the memory that the
 140        expression touches in the course of evaluation, so that memory will
 141        be available when the user later tries to evaluate the expression
 142        in GDB.
 143
 144        Setting the flag 'tracing' to non-zero enables the code that
 145        emits the trace bytecodes at the appropriate points.  */
 146
 147     unsigned int tracing : 1;
 148
 149     /* This indicates that pointers to chars should get an added
 150        tracenz bytecode to record nonzero bytes, up to a length that
 151        is the value of trace_string.  */
 152
 153     int trace_string;
 154   };
 155
 156 /* An agent_expr owning pointer.  */
 157 typedef std::unique_ptr<agent_expr> agent_expr_up;
 158
 159 /* The actual values of the various bytecode operations.  */
 160
 161 enum agent_op
 162   {
 163 #define DEFOP(NAME, SIZE, DATA_SIZE, CONSUMED, PRODUCED, VALUE)  \
 164     aop_ ## NAME = VALUE,
 165 #include "gdbsupport/ax.def"
 166 #undef DEFOP
 167     aop_last
 168   };
 169 \f
 170
 171
 172 /* Functions for building expressions.  */
 173
 174 /* Append a raw byte to EXPR.  */
 175 extern void ax_raw_byte (struct agent_expr *expr, gdb_byte byte);
 176
 177 /* Append a simple operator OP to EXPR.  */
 178 extern void ax_simple (struct agent_expr *EXPR, enum agent_op OP);
 179
 180 /* Append a pick operator to EXPR.  DEPTH is the stack item to pick,
 181    with 0 being top of stack.  */
 182 extern void ax_pick (struct agent_expr *EXPR, int DEPTH);
 183
 184 /* Append the floating-point prefix, for the next bytecode.  */
 185 #define ax_float(EXPR) (ax_simple ((EXPR), aop_float))
 186
 187 /* Append a sign-extension instruction to EXPR, to extend an N-bit value.  */
 188 extern void ax_ext (struct agent_expr *EXPR, int N);
 189
 190 /* Append a zero-extension instruction to EXPR, to extend an N-bit value.  */
 191 extern void ax_zero_ext (struct agent_expr *EXPR, int N);
 192
 193 /* Append a trace_quick instruction to EXPR, to record N bytes.  */
 194 extern void ax_trace_quick (struct agent_expr *EXPR, int N);
 195
 196 /* Append a goto op to EXPR.  OP is the actual op (must be aop_goto or
 197    aop_if_goto).  We assume we don't know the target offset yet,
 198    because it's probably a forward branch, so we leave space in EXPR
 199    for the target, and return the offset in EXPR of that space, so we
 200    can backpatch it once we do know the target offset.  Use ax_label
 201    to do the backpatching.  */
 202 extern int ax_goto (struct agent_expr *EXPR, enum agent_op OP);
 203
 204 /* Suppose a given call to ax_goto returns some value PATCH.  When you
 205    know the offset TARGET that goto should jump to, call
 206    ax_label (EXPR, PATCH, TARGET)
 207    to patch TARGET into the ax_goto instruction.  */
 208 extern void ax_label (struct agent_expr *EXPR, int patch, int target);
 209
 210 /* Assemble code to push a constant on the stack.  */
 211 extern void ax_const_l (struct agent_expr *EXPR, LONGEST l);
 212 extern void ax_const_d (struct agent_expr *EXPR, LONGEST d);
 213
 214 /* Assemble code to push the value of register number REG on the
 215    stack.  */
 216 extern void ax_reg (struct agent_expr *EXPR, int REG);
 217
 218 /* Add the given register to the register mask of the expression.  */
 219 extern void ax_reg_mask (struct agent_expr *ax, int reg);
 220
 221 /* Assemble code to operate on a trace state variable.  */
 222 extern void ax_tsv (struct agent_expr *expr, enum agent_op op, int num);
 223
 224 /* Append a string to the bytecode stream.  */
 225 extern void ax_string (struct agent_expr *x, const char *str, int slen);
 226 \f
 227
 228 /* Functions for printing out expressions, and otherwise debugging
 229    things.  */
 230
 231 /* Disassemble the expression EXPR, writing to F.  */
 232 extern void ax_print (struct ui_file *f, struct agent_expr * EXPR);
 233
 234 /* An entry in the opcode map.  */
 235 struct aop_map
 236   {
 237
 238     /* The name of the opcode.  Null means that this entry is not a
 239        valid opcode --- a hole in the opcode space.  */
 240     const char *name;
 241
 242     /* All opcodes take no operands from the bytecode stream, or take
 243        unsigned integers of various sizes.  If this is a positive number
 244        n, then the opcode is followed by an n-byte operand, which should
 245        be printed as an unsigned integer.  If this is zero, then the
 246        opcode takes no operands from the bytecode stream.
 247
 248        If we get more complicated opcodes in the future, don't add other
 249        magic values of this; that's a crock.  Add an `enum encoding'
 250        field to this, or something like that.  */
 251     int op_size;
 252
 253     /* The size of the data operated upon, in bits, for bytecodes that
 254        care about that (ref and const).  Zero for all others.  */
 255     int data_size;
 256
 257     /* Number of stack elements consumed, and number produced.  */
 258     int consumed, produced;
 259   };
 260
 261 /* Map of the bytecodes, indexed by bytecode number.  */
 262 extern struct aop_map aop_map[];
 263
 264 /* Given an agent expression AX, analyze and update its requirements.  */
 265
 266 extern void ax_reqs (struct agent_expr *ax);
 267
 268 #endif /* AX_H */