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/* GDB-specific functions for operating on agent expressions

   Copyright (C) 1998, 1999, 2000, 2007, 2008, 2009, 2010

   Free Software Foundation, Inc.

   This file is part of GDB.

   This program is free software; you can redistribute it and/or modify

   it under the terms of the GNU General Public License as published by

   the Free Software Foundation; either version 3 of the License, or

   (at your option) any later version.

   This program is distributed in the hope that it will be useful,

   but WITHOUT ANY WARRANTY; without even the implied warranty of

   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License

   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */

#ifndef AX_GDB_H

#define AX_GDB_H

struct expression;

/* Types and enums */

/* GDB stores expressions in the form of a flattened tree (struct

   expression), so we just walk that tree and generate agent bytecodes

   as we go along.

   GDB's normal evaluation uses struct value, which contains the

   expression's value as well as its address or the register it came

   from.  The `+' operator uses the value, whereas the unary `&'

   operator will use the address portion.  The `=' operator will use

   the address or register number of its left hand side.

   The issues are different when generating agent bytecode.  Given a

   variable reference expression, we should not necessarily generate

   code to fetch its value, because the next operator may be `=' or

   unary `&'.  Instead, when we recurse on a subexpression, we

   indicate whether we want that expression to produce an lvalue or an

   rvalue.  If we requested an lvalue, then the recursive call tells

   us whether it generated code to compute an address on the stack, or

   whether the lvalue lives in a register.

   The `axs' prefix here means `agent expression, static', because

   this is all static analysis of the expression, i.e. analysis which

   doesn't depend on the contents of memory and registers.  */

/* Different kinds of agent expression static values.  */

enum axs_lvalue_kind

  {

    /* We generated code to compute the subexpression's value.

       Constants and arithmetic operators yield this.  */

    axs_rvalue,

    /* We generated code to yield the subexpression's value's address on

       the top of the stack.  If the caller needs an rvalue, it should

       call require_rvalue to produce the rvalue from this address.  */

    axs_lvalue_memory,

    /* We didn't generate any code, and the stack is undisturbed,

       because the subexpression's value lives in a register; u.reg is

       the register number.  If the caller needs an rvalue, it should

       call require_rvalue to produce the rvalue from this register

       number.  */

    axs_lvalue_register

  };

/* Structure describing what we got from a subexpression.  Think of

   this as parallel to value.h's enum lval_type, except that we're

   describing a value which will exist when the expression is

   evaluated in the future, not a value we have in our hand.  */

struct axs_value

  {

    enum axs_lvalue_kind kind;  /* see above */

    /* The type of the subexpression.  Even if lvalue == axs_lvalue_memory,

       this is the type of the value itself; the value on the stack is a

       "pointer to" an object of this type. */

    struct type *type;

    union

      {

        /* if kind == axs_lvalue_register, this is the register number */

        int reg;

      }

    u;

  };

/* Translating GDB expressions into agent expressions.  */

/* Given a GDB expression EXPR, return bytecode to trace its value.

   The result will use the `trace' and `trace_quick' bytecodes to

   record the value of all memory touched by the expression, and leave

   no values on the stack.  The caller can then use the ax_reqs

   function to discover which registers the expression uses.  */

extern struct agent_expr *gen_trace_for_expr (CORE_ADDR, struct expression *);

extern struct agent_expr *gen_trace_for_var (CORE_ADDR, struct symbol *);

extern struct agent_expr *gen_eval_for_expr (CORE_ADDR, struct expression *);

#endif /* AX_GDB_H */