gdb/ax-gdb.h

   1 /* GDB-specific functions for operating on agent expressions
   2    Copyright (C) 1998-2020 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 #include "ax.h"  /* For agent_expr_up.  */
  23
  24 struct expression;
  25 union exp_element;
  26
  27 /* Types and enums */
  28
  29 /* GDB stores expressions in the form of a flattened tree (struct
  30    expression), so we just walk that tree and generate agent bytecodes
  31    as we go along.
  32
  33    GDB's normal evaluation uses struct value, which contains the
  34    expression's value as well as its address or the register it came
  35    from.  The `+' operator uses the value, whereas the unary `&'
  36    operator will use the address portion.  The `=' operator will use
  37    the address or register number of its left hand side.
  38
  39    The issues are different when generating agent bytecode.  Given a
  40    variable reference expression, we should not necessarily generate
  41    code to fetch its value, because the next operator may be `=' or
  42    unary `&'.  Instead, when we recurse on a subexpression, we
  43    indicate whether we want that expression to produce an lvalue or an
  44    rvalue.  If we requested an lvalue, then the recursive call tells
  45    us whether it generated code to compute an address on the stack, or
  46    whether the lvalue lives in a register.
  47
  48    The `axs' prefix here means `agent expression, static', because
  49    this is all static analysis of the expression, i.e. analysis which
  50    doesn't depend on the contents of memory and registers.  */
  51
  52
  53 /* Different kinds of agent expression static values.  */
  54 enum axs_lvalue_kind
  55   {
  56     /* We generated code to compute the subexpression's value.
  57        Constants and arithmetic operators yield this.  */
  58     axs_rvalue,
  59
  60     /* We generated code to yield the subexpression's value's address on
  61        the top of the stack.  If the caller needs an rvalue, it should
  62        call require_rvalue to produce the rvalue from this address.  */
  63     axs_lvalue_memory,
  64
  65     /* We didn't generate any code, and the stack is undisturbed,
  66        because the subexpression's value lives in a register; u.reg is
  67        the register number.  If the caller needs an rvalue, it should
  68        call require_rvalue to produce the rvalue from this register
  69        number.  */
  70     axs_lvalue_register
  71   };
  72
  73 /* Structure describing what we got from a subexpression.  Think of
  74    this as parallel to value.h's enum lval_type, except that we're
  75    describing a value which will exist when the expression is
  76    evaluated in the future, not a value we have in our hand.  */
  77 struct axs_value
  78   {
  79     enum axs_lvalue_kind kind;  /* see above */
  80
  81     /* The type of the subexpression.  Even if lvalue == axs_lvalue_memory,
  82        this is the type of the value itself; the value on the stack is a
  83        "pointer to" an object of this type.  */
  84     struct type *type;
  85
  86     /* If nonzero, this is a variable which does not actually exist in
  87        the program.  */
  88     char optimized_out;
  89
  90     union
  91       {
  92         /* if kind == axs_lvalue_register, this is the register number */
  93         int reg;
  94       }
  95     u;
  96   };
  97 \f
  98
  99 /* Translating GDB expressions into agent expressions.  */
 100
 101 /* Given a GDB expression EXPR, return bytecode to trace its value.
 102    The result will use the `trace' and `trace_quick' bytecodes to
 103    record the value of all memory touched by the expression, and leave
 104    no values on the stack.  The caller can then use the ax_reqs
 105    function to discover which registers the expression uses.  */
 106 extern agent_expr_up gen_trace_for_expr (CORE_ADDR, struct expression *,
 107                                          int);
 108
 109 extern agent_expr_up gen_trace_for_var (CORE_ADDR, struct gdbarch *,
 110                                         struct symbol *, int);
 111
 112 extern agent_expr_up gen_trace_for_return_address (CORE_ADDR,
 113                                                    struct gdbarch *,
 114                                                    int);
 115
 116 extern agent_expr_up gen_eval_for_expr (CORE_ADDR, struct expression *);
 117
 118 extern void gen_expr (struct expression *exp, union exp_element **pc,
 119                       struct agent_expr *ax, struct axs_value *value);
 120
 121 extern void require_rvalue (struct agent_expr *ax, struct axs_value *value);
 122
 123 extern agent_expr_up gen_printf (CORE_ADDR, struct gdbarch *,
 124                                  CORE_ADDR, LONGEST, const char *, int,
 125                                  int, struct expression **);
 126
 127 #endif /* AX_GDB_H */