gdb/ax.h

   1 /* Definitions for expressions designed to be executed on the agent
   2    Copyright (C) 1998-2023 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     agent_expr (struct gdbarch *gdbarch, CORE_ADDR scope)
  85       : gdbarch (gdbarch),
  86         scope (scope)
  87     { }
  88
  89     /* The bytes of the expression.  */
  90     gdb::byte_vector buf;
  91
  92     /* The target architecture assumed to be in effect.  */
  93     struct gdbarch *gdbarch;
  94
  95     /* The address to which the expression applies.  */
  96     CORE_ADDR scope;
  97
  98     /* If the following is not equal to agent_flaw_none, the rest of the
  99        information in this structure is suspect.  */
 100     enum agent_flaws flaw;
 101
 102     /* Number of elements left on stack at end; may be negative if expr
 103        only consumes elements.  */
 104     int final_height;
 105
 106     /* Maximum and minimum stack height, relative to initial height.  */
 107     int max_height, min_height;
 108
 109     /* Largest `ref' or `const' opcode used, in bits.  Zero means the
 110        expression has no such instructions.  */
 111     int max_data_size;
 112
 113     /* Bit vector of registers needed.  Register R is needed iff
 114        reg_mask[R] is non-zero.  Note!  You may not assume that this
 115        bitmask is long enough to hold bits for all the registers of
 116        the machine; the agent expression code has no idea how many
 117        registers the machine has.
 118
 119        Also note that this mask may contain registers that are needed
 120        for the original collection expression to work, but that are
 121        not referenced by any bytecode.  This could, for example, occur
 122        when collecting a local variable allocated to a register; the
 123        compiler sets the mask bit and skips generating a bytecode whose
 124        result is going to be discarded anyway.
 125     */
 126     std::vector<bool> reg_mask;
 127
 128     /* For the data tracing facility, we need to insert `trace' bytecodes
 129        before each data fetch; this records all the memory that the
 130        expression touches in the course of evaluation, so that memory will
 131        be available when the user later tries to evaluate the expression
 132        in GDB.
 133
 134        Setting the flag 'tracing' to true enables the code that
 135        emits the trace bytecodes at the appropriate points.  */
 136
 137     bool tracing = false;
 138
 139     /* This indicates that pointers to chars should get an added
 140        tracenz bytecode to record nonzero bytes, up to a length that
 141        is the value of trace_string.  */
 142
 143     int trace_string = 0;
 144   };
 145
 146 /* An agent_expr owning pointer.  */
 147 typedef std::unique_ptr<agent_expr> agent_expr_up;
 148
 149 /* The actual values of the various bytecode operations.  */
 150
 151 enum agent_op
 152   {
 153 #define DEFOP(NAME, SIZE, DATA_SIZE, CONSUMED, PRODUCED, VALUE)  \
 154     aop_ ## NAME = VALUE,
 155 #include "gdbsupport/ax.def"
 156 #undef DEFOP
 157   };
 158 \f
 159
 160
 161 /* Functions for building expressions.  */
 162
 163 /* Append a raw byte to EXPR.  */
 164 extern void ax_raw_byte (struct agent_expr *expr, gdb_byte byte);
 165
 166 /* Append a simple operator OP to EXPR.  */
 167 extern void ax_simple (struct agent_expr *EXPR, enum agent_op OP);
 168
 169 /* Append a pick operator to EXPR.  DEPTH is the stack item to pick,
 170    with 0 being top of stack.  */
 171 extern void ax_pick (struct agent_expr *EXPR, int DEPTH);
 172
 173 /* Append the floating-point prefix, for the next bytecode.  */
 174 #define ax_float(EXPR) (ax_simple ((EXPR), aop_float))
 175
 176 /* Append a sign-extension instruction to EXPR, to extend an N-bit value.  */
 177 extern void ax_ext (struct agent_expr *EXPR, int N);
 178
 179 /* Append a zero-extension instruction to EXPR, to extend an N-bit value.  */
 180 extern void ax_zero_ext (struct agent_expr *EXPR, int N);
 181
 182 /* Append a trace_quick instruction to EXPR, to record N bytes.  */
 183 extern void ax_trace_quick (struct agent_expr *EXPR, int N);
 184
 185 /* Append a goto op to EXPR.  OP is the actual op (must be aop_goto or
 186    aop_if_goto).  We assume we don't know the target offset yet,
 187    because it's probably a forward branch, so we leave space in EXPR
 188    for the target, and return the offset in EXPR of that space, so we
 189    can backpatch it once we do know the target offset.  Use ax_label
 190    to do the backpatching.  */
 191 extern int ax_goto (struct agent_expr *EXPR, enum agent_op OP);
 192
 193 /* Suppose a given call to ax_goto returns some value PATCH.  When you
 194    know the offset TARGET that goto should jump to, call
 195    ax_label (EXPR, PATCH, TARGET)
 196    to patch TARGET into the ax_goto instruction.  */
 197 extern void ax_label (struct agent_expr *EXPR, int patch, int target);
 198
 199 /* Assemble code to push a constant on the stack.  */
 200 extern void ax_const_l (struct agent_expr *EXPR, LONGEST l);
 201 extern void ax_const_d (struct agent_expr *EXPR, LONGEST d);
 202
 203 /* Assemble code to push the value of register number REG on the
 204    stack.  */
 205 extern void ax_reg (struct agent_expr *EXPR, int REG);
 206
 207 /* Add the given register to the register mask of the expression.  */
 208 extern void ax_reg_mask (struct agent_expr *ax, int reg);
 209
 210 /* Assemble code to operate on a trace state variable.  */
 211 extern void ax_tsv (struct agent_expr *expr, enum agent_op op, int num);
 212
 213 /* Append a string to the bytecode stream.  */
 214 extern void ax_string (struct agent_expr *x, const char *str, int slen);
 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 /* Given an agent expression AX, analyze and update its requirements.  */
 224
 225 extern void ax_reqs (struct agent_expr *ax);
 226
 227 #endif /* AX_H */