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269 lines
9.9 KiB
C++
269 lines
9.9 KiB
C++
/* Definitions for expressions designed to be executed on the agent
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Copyright (C) 1998-2020 Free Software Foundation, Inc.
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This file is part of GDB.
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 3 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program. If not, see <http://www.gnu.org/licenses/>. */
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#ifndef AX_H
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#define AX_H
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/* It's sometimes useful to be able to debug programs that you can't
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really stop for more than a fraction of a second. To this end, the
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user can specify a tracepoint (like a breakpoint, but you don't
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stop at it), and specify a bunch of expressions to record the
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values of when that tracepoint is reached. As the program runs,
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GDB collects the values. At any point (possibly while values are
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still being collected), the user can display the collected values.
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This is used with remote debugging; we don't really support it on
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native configurations.
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This means that expressions are being evaluated by the remote agent,
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which doesn't have any access to the symbol table information, and
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needs to be small and simple.
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The agent_expr routines and datatypes are a bytecode language
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designed to be executed by the agent. Agent expressions work in
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terms of fixed-width values, operators, memory references, and
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register references. You can evaluate a agent expression just given
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a bunch of memory and register values to sniff at; you don't need
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any symbolic information like variable names, types, etc.
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GDB translates source expressions, whose meaning depends on
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symbolic information, into agent bytecode expressions, whose meaning
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is independent of symbolic information. This means the agent can
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evaluate them on the fly without reference to data only available
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to the host GDB. */
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/* Different kinds of flaws an agent expression might have, as
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detected by ax_reqs. */
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enum agent_flaws
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{
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agent_flaw_none = 0, /* code is good */
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/* There is an invalid instruction in the stream. */
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agent_flaw_bad_instruction,
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/* There is an incomplete instruction at the end of the expression. */
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agent_flaw_incomplete_instruction,
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/* ax_reqs was unable to prove that every jump target is to a
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valid offset. Valid offsets are within the bounds of the
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expression, and to a valid instruction boundary. */
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agent_flaw_bad_jump,
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/* ax_reqs was unable to prove to its satisfaction that, for each
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jump target location, the stack will have the same height whether
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that location is reached via a jump or by straight execution. */
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agent_flaw_height_mismatch,
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/* ax_reqs was unable to prove that every instruction following
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an unconditional jump was the target of some other jump. */
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agent_flaw_hole
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};
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/* Agent expression data structures. */
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/* A buffer containing a agent expression. */
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struct agent_expr
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{
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/* Construct an empty agent expression. */
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explicit agent_expr (struct gdbarch *gdbarch, CORE_ADDR scope);
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~agent_expr ();
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/* The bytes of the expression. */
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unsigned char *buf;
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/* The number of bytecode in the expression. */
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int len;
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/* Allocated space available currently. */
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int size;
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/* The target architecture assumed to be in effect. */
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struct gdbarch *gdbarch;
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/* The address to which the expression applies. */
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CORE_ADDR scope;
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/* If the following is not equal to agent_flaw_none, the rest of the
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information in this structure is suspect. */
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enum agent_flaws flaw;
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/* Number of elements left on stack at end; may be negative if expr
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only consumes elements. */
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int final_height;
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/* Maximum and minimum stack height, relative to initial height. */
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int max_height, min_height;
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/* Largest `ref' or `const' opcode used, in bits. Zero means the
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expression has no such instructions. */
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int max_data_size;
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/* Bit vector of registers needed. Register R is needed iff
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reg_mask[R / 8] & (1 << (R % 8))
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is non-zero. Note! You may not assume that this bitmask is long
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enough to hold bits for all the registers of the machine; the
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agent expression code has no idea how many registers the machine
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has. However, the bitmask is reg_mask_len bytes long, so the
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valid register numbers run from 0 to reg_mask_len * 8 - 1.
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Also note that this mask may contain registers that are needed
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for the original collection expression to work, but that are
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not referenced by any bytecode. This could, for example, occur
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when collecting a local variable allocated to a register; the
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compiler sets the mask bit and skips generating a bytecode whose
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result is going to be discarded anyway.
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*/
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int reg_mask_len;
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unsigned char *reg_mask;
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/* For the data tracing facility, we need to insert `trace' bytecodes
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before each data fetch; this records all the memory that the
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expression touches in the course of evaluation, so that memory will
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be available when the user later tries to evaluate the expression
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in GDB.
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Setting the flag 'tracing' to non-zero enables the code that
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emits the trace bytecodes at the appropriate points. */
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unsigned int tracing : 1;
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/* This indicates that pointers to chars should get an added
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tracenz bytecode to record nonzero bytes, up to a length that
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is the value of trace_string. */
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int trace_string;
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};
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/* An agent_expr owning pointer. */
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typedef std::unique_ptr<agent_expr> agent_expr_up;
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/* The actual values of the various bytecode operations. */
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enum agent_op
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{
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#define DEFOP(NAME, SIZE, DATA_SIZE, CONSUMED, PRODUCED, VALUE) \
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aop_ ## NAME = VALUE,
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#include "gdbsupport/ax.def"
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#undef DEFOP
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aop_last
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};
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/* Functions for building expressions. */
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/* Append a raw byte to EXPR. */
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extern void ax_raw_byte (struct agent_expr *expr, gdb_byte byte);
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/* Append a simple operator OP to EXPR. */
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extern void ax_simple (struct agent_expr *EXPR, enum agent_op OP);
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/* Append a pick operator to EXPR. DEPTH is the stack item to pick,
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with 0 being top of stack. */
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extern void ax_pick (struct agent_expr *EXPR, int DEPTH);
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/* Append the floating-point prefix, for the next bytecode. */
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#define ax_float(EXPR) (ax_simple ((EXPR), aop_float))
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/* Append a sign-extension instruction to EXPR, to extend an N-bit value. */
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extern void ax_ext (struct agent_expr *EXPR, int N);
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/* Append a zero-extension instruction to EXPR, to extend an N-bit value. */
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extern void ax_zero_ext (struct agent_expr *EXPR, int N);
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/* Append a trace_quick instruction to EXPR, to record N bytes. */
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extern void ax_trace_quick (struct agent_expr *EXPR, int N);
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/* Append a goto op to EXPR. OP is the actual op (must be aop_goto or
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aop_if_goto). We assume we don't know the target offset yet,
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because it's probably a forward branch, so we leave space in EXPR
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for the target, and return the offset in EXPR of that space, so we
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can backpatch it once we do know the target offset. Use ax_label
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to do the backpatching. */
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extern int ax_goto (struct agent_expr *EXPR, enum agent_op OP);
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/* Suppose a given call to ax_goto returns some value PATCH. When you
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know the offset TARGET that goto should jump to, call
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ax_label (EXPR, PATCH, TARGET)
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to patch TARGET into the ax_goto instruction. */
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extern void ax_label (struct agent_expr *EXPR, int patch, int target);
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/* Assemble code to push a constant on the stack. */
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extern void ax_const_l (struct agent_expr *EXPR, LONGEST l);
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extern void ax_const_d (struct agent_expr *EXPR, LONGEST d);
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/* Assemble code to push the value of register number REG on the
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stack. */
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extern void ax_reg (struct agent_expr *EXPR, int REG);
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/* Add the given register to the register mask of the expression. */
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extern void ax_reg_mask (struct agent_expr *ax, int reg);
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/* Assemble code to operate on a trace state variable. */
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extern void ax_tsv (struct agent_expr *expr, enum agent_op op, int num);
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/* Append a string to the bytecode stream. */
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extern void ax_string (struct agent_expr *x, const char *str, int slen);
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/* Functions for printing out expressions, and otherwise debugging
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things. */
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/* Disassemble the expression EXPR, writing to F. */
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extern void ax_print (struct ui_file *f, struct agent_expr * EXPR);
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/* An entry in the opcode map. */
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struct aop_map
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{
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/* The name of the opcode. Null means that this entry is not a
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valid opcode --- a hole in the opcode space. */
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const char *name;
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/* All opcodes take no operands from the bytecode stream, or take
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unsigned integers of various sizes. If this is a positive number
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n, then the opcode is followed by an n-byte operand, which should
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be printed as an unsigned integer. If this is zero, then the
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opcode takes no operands from the bytecode stream.
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If we get more complicated opcodes in the future, don't add other
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magic values of this; that's a crock. Add an `enum encoding'
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field to this, or something like that. */
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int op_size;
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/* The size of the data operated upon, in bits, for bytecodes that
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care about that (ref and const). Zero for all others. */
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int data_size;
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/* Number of stack elements consumed, and number produced. */
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int consumed, produced;
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};
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/* Map of the bytecodes, indexed by bytecode number. */
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extern struct aop_map aop_map[];
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/* Given an agent expression AX, analyze and update its requirements. */
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extern void ax_reqs (struct agent_expr *ax);
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#endif /* AX_H */
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