gdb/ax-gdb.h

   1 /* GDB-specific functions for operating on agent expressions
   2    Copyright (C) 1998-2022 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
  26 /* Types and enums */
  27
  28 /* GDB stores expressions in the form of a flattened tree (struct
  29    expression), so we just walk that tree and generate agent bytecodes
  30    as we go along.
  31
  32    GDB's normal evaluation uses struct value, which contains the
  33    expression's value as well as its address or the register it came
  34    from.  The `+' operator uses the value, whereas the unary `&'
  35    operator will use the address portion.  The `=' operator will use
  36    the address or register number of its left hand side.
  37
  38    The issues are different when generating agent bytecode.  Given a
  39    variable reference expression, we should not necessarily generate
  40    code to fetch its value, because the next operator may be `=' or
  41    unary `&'.  Instead, when we recurse on a subexpression, we
  42    indicate whether we want that expression to produce an lvalue or an
  43    rvalue.  If we requested an lvalue, then the recursive call tells
  44    us whether it generated code to compute an address on the stack, or
  45    whether the lvalue lives in a register.
  46
  47    The `axs' prefix here means `agent expression, static', because
  48    this is all static analysis of the expression, i.e. analysis which
  49    doesn't depend on the contents of memory and registers.  */
  50
  51
  52 /* Different kinds of agent expression static values.  */
  53 enum axs_lvalue_kind
  54   {
  55     /* We generated code to compute the subexpression's value.
  56        Constants and arithmetic operators yield this.  */
  57     axs_rvalue,
  58
  59     /* We generated code to yield the subexpression's value's address on
  60        the top of the stack.  If the caller needs an rvalue, it should
  61        call require_rvalue to produce the rvalue from this address.  */
  62     axs_lvalue_memory,
  63
  64     /* We didn't generate any code, and the stack is undisturbed,
  65        because the subexpression's value lives in a register; u.reg is
  66        the register number.  If the caller needs an rvalue, it should
  67        call require_rvalue to produce the rvalue from this register
  68        number.  */
  69     axs_lvalue_register
  70   };
  71
  72 /* Structure describing what we got from a subexpression.  Think of
  73    this as parallel to value.h's enum lval_type, except that we're
  74    describing a value which will exist when the expression is
  75    evaluated in the future, not a value we have in our hand.  */
  76 struct axs_value
  77   {
  78     enum axs_lvalue_kind kind;  /* see above */
  79
  80     /* The type of the subexpression.  Even if lvalue == axs_lvalue_memory,
  81        this is the type of the value itself; the value on the stack is a
  82        "pointer to" an object of this type.  */
  83     struct type *type;
  84
  85     /* If nonzero, this is a variable which does not actually exist in
  86        the program.  */
  87     char optimized_out;
  88
  89     union
  90       {
  91         /* if kind == axs_lvalue_register, this is the register number */
  92         int reg;
  93       }
  94     u;
  95   };
  96 \f
  97
  98 /* Translating GDB expressions into agent expressions.  */
  99
 100 /* Given a GDB expression EXPR, return bytecode to trace its value.
 101    The result will use the `trace' and `trace_quick' bytecodes to
 102    record the value of all memory touched by the expression, and leave
 103    no values on the stack.  The caller can then use the ax_reqs
 104    function to discover which registers the expression uses.  */
 105 extern agent_expr_up gen_trace_for_expr (CORE_ADDR, struct expression *,
 106                                          int);
 107
 108 extern agent_expr_up gen_trace_for_var (CORE_ADDR, struct gdbarch *,
 109                                         struct symbol *, int);
 110
 111 extern agent_expr_up gen_trace_for_return_address (CORE_ADDR,
 112                                                    struct gdbarch *,
 113                                                    int);
 114
 115 extern agent_expr_up gen_eval_for_expr (CORE_ADDR, struct expression *);
 116
 117 extern void gen_expr (struct expression *exp, union exp_element **pc,
 118                       struct agent_expr *ax, struct axs_value *value);
 119
 120 extern void require_rvalue (struct agent_expr *ax, struct axs_value *value);
 121
 122 extern agent_expr_up gen_printf (CORE_ADDR, struct gdbarch *,
 123                                  CORE_ADDR, LONGEST, const char *, int,
 124                                  int, struct expression **);
 125
 126 #endif /* AX_GDB_H */