1/* GDB-specific functions for operating on agent expressions
2   Copyright (C) 1998, 1999, 2000, 2007 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_GDB_H
20#define AX_GDB_H
21
22struct expression;
23
24/* Types and enums */
25
26/* GDB stores expressions in the form of a flattened tree (struct
27   expression), so we just walk that tree and generate agent bytecodes
28   as we go along.
29
30   GDB's normal evaluation uses struct value, which contains the
31   expression's value as well as its address or the register it came
32   from.  The `+' operator uses the value, whereas the unary `&'
33   operator will use the address portion.  The `=' operator will use
34   the address or register number of its left hand side.
35
36   The issues are different when generating agent bytecode.  Given a
37   variable reference expression, we should not necessarily generate
38   code to fetch its value, because the next operator may be `=' or
39   unary `&'.  Instead, when we recurse on a subexpression, we
40   indicate whether we want that expression to produce an lvalue or an
41   rvalue.  If we requested an lvalue, then the recursive call tells
42   us whether it generated code to compute an address on the stack, or
43   whether the lvalue lives in a register.
44
45   The `axs' prefix here means `agent expression, static', because
46   this is all static analysis of the expression, i.e. analysis which
47   doesn't depend on the contents of memory and registers.  */
48
49
50/* Different kinds of agent expression static values.  */
51enum axs_lvalue_kind
52  {
53    /* We generated code to compute the subexpression's value.
54       Constants and arithmetic operators yield this.  */
55    axs_rvalue,
56
57    /* We generated code to yield the subexpression's value's address on
58       the top of the stack.  If the caller needs an rvalue, it should
59       call require_rvalue to produce the rvalue from this address.  */
60    axs_lvalue_memory,
61
62    /* We didn't generate any code, and the stack is undisturbed,
63       because the subexpression's value lives in a register; u.reg is
64       the register number.  If the caller needs an rvalue, it should
65       call require_rvalue to produce the rvalue from this register
66       number.  */
67    axs_lvalue_register
68  };
69
70/* Structure describing what we got from a subexpression.  Think of
71   this as parallel to value.h's enum lval_type, except that we're
72   describing a value which will exist when the expression is
73   evaluated in the future, not a value we have in our hand.  */
74struct axs_value
75  {
76    enum axs_lvalue_kind kind;	/* see above */
77
78    /* The type of the subexpression.  Even if lvalue == axs_lvalue_memory,
79       this is the type of the value itself; the value on the stack is a
80       "pointer to" an object of this type. */
81    struct type *type;
82
83    union
84      {
85	/* if kind == axs_lvalue_register, this is the register number */
86	int reg;
87      }
88    u;
89  };
90
91
92/* Translating GDB expressions into agent expressions.  */
93
94/* Given a GDB expression EXPR, translate it into the agent bytecode,
95   and return it.  FLAGS are from enum expr_to_agent_flags.  */
96extern struct agent_expr *expr_to_agent (struct expression *EXPR,
97					 struct axs_value *VALUE);
98
99/* Given a GDB expression EXPR denoting an lvalue in memory, produce a
100   string of agent bytecode which will leave its address and size on
101   the top of stack.  Return the agent expression.  */
102extern struct agent_expr *expr_to_address_and_size (struct expression *EXPR);
103
104/* Given a GDB expression EXPR, return bytecode to trace its value.
105   The result will use the `trace' and `trace_quick' bytecodes to
106   record the value of all memory touched by the expression, and leave
107   no values on the stack.  The caller can then use the ax_reqs
108   function to discover which registers the expression uses.  */
109extern struct agent_expr *gen_trace_for_expr (CORE_ADDR, struct expression *);
110
111#endif /* AX_GDB_H */
112