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+/* GDB-specific functions for operating on agent expressions
+   Copyright 1998 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 2 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, write to the Free Software
+Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.  */
+
+/* $Id$ */
+
+#ifndef AX_GDB_H
+#define AX_GDB_H
+
+
+/* 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, translate it into the agent bytecode,
+   and return it.  FLAGS are from enum expr_to_agent_flags.  */
+extern struct agent_expr *expr_to_agent PARAMS ((struct expression *EXPR,
+						 struct axs_value *VALUE));
+
+/* Given a GDB expression EXPR denoting an lvalue in memory, produce a
+   string of agent bytecode which will leave its address and size on
+   the top of stack.  Return the agent expression.  */
+extern struct agent_expr *expr_to_address_and_size
+			  PARAMS ((struct expression *EXPR));
+
+/* 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 PARAMS ((CORE_ADDR, 
+						      struct expression *));
+
+#endif /* AX_GDB_H */