1 /* GDB-specific functions for operating on agent expressions
2 Copyright (C) 1998, 1999, 2000, 2007, 2008 Free Software Foundation, Inc.
4 This file is part of GDB.
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.
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.
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/>. */
26 /* GDB stores expressions in the form of a flattened tree (struct
27 expression), so we just walk that tree and generate agent bytecodes
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.
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.
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. */
50 /* Different kinds of agent expression static values. */
53 /* We generated code to compute the subexpression's value.
54 Constants and arithmetic operators yield this. */
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. */
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
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. */
76 enum axs_lvalue_kind kind
; /* see above */
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. */
85 /* if kind == axs_lvalue_register, this is the register number */
92 /* Translating GDB expressions into agent expressions. */
94 /* Given a GDB expression EXPR, return bytecode to trace its value.
95 The result will use the `trace' and `trace_quick' bytecodes to
96 record the value of all memory touched by the expression, and leave
97 no values on the stack. The caller can then use the ax_reqs
98 function to discover which registers the expression uses. */
99 extern struct agent_expr
*gen_trace_for_expr (CORE_ADDR
, struct expression
*);
101 #endif /* AX_GDB_H */
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