gdb/ax-gdb.h

   1 /* GDB-specific functions for operating on agent expressions
   2    Copyright (C) 1998, 1999, 2000, 2007, 2008 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
  22 struct 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.  */
  51 enum 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.  */
  74 struct 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 \f
  91
  92 /* Translating GDB expressions into agent expressions.  */
  93
  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 *);
 100
 101 #endif /* AX_GDB_H */