545 lines
13 KiB
C
545 lines
13 KiB
C
/* Prologue value handling for GDB.
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Copyright (C) 2003-2020 Free Software Foundation, Inc.
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This file is part of GDB.
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 3 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program. If not, see <http://www.gnu.org/licenses/>. */
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#include "defs.h"
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#include "prologue-value.h"
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#include "regcache.h"
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/* Constructors. */
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pv_t
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pv_unknown (void)
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{
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pv_t v = { pvk_unknown, 0, 0 };
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return v;
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}
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pv_t
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pv_constant (CORE_ADDR k)
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{
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pv_t v;
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v.kind = pvk_constant;
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v.reg = -1; /* for debugging */
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v.k = k;
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return v;
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}
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pv_t
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pv_register (int reg, CORE_ADDR k)
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{
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pv_t v;
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v.kind = pvk_register;
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v.reg = reg;
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v.k = k;
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return v;
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}
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/* Arithmetic operations. */
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/* If one of *A and *B is a constant, and the other isn't, swap the
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values as necessary to ensure that *B is the constant. This can
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reduce the number of cases we need to analyze in the functions
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below. */
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static void
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constant_last (pv_t *a, pv_t *b)
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{
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if (a->kind == pvk_constant
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&& b->kind != pvk_constant)
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{
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pv_t temp = *a;
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*a = *b;
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*b = temp;
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}
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}
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pv_t
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pv_add (pv_t a, pv_t b)
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{
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constant_last (&a, &b);
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/* We can add a constant to a register. */
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if (a.kind == pvk_register
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&& b.kind == pvk_constant)
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return pv_register (a.reg, a.k + b.k);
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/* We can add a constant to another constant. */
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else if (a.kind == pvk_constant
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&& b.kind == pvk_constant)
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return pv_constant (a.k + b.k);
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/* Anything else we don't know how to add. We don't have a
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representation for, say, the sum of two registers, or a multiple
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of a register's value (adding a register to itself). */
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else
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return pv_unknown ();
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}
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pv_t
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pv_add_constant (pv_t v, CORE_ADDR k)
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{
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/* Rather than thinking of all the cases we can and can't handle,
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we'll just let pv_add take care of that for us. */
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return pv_add (v, pv_constant (k));
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}
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pv_t
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pv_subtract (pv_t a, pv_t b)
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{
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/* This isn't quite the same as negating B and adding it to A, since
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we don't have a representation for the negation of anything but a
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constant. For example, we can't negate { pvk_register, R1, 10 },
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but we do know that { pvk_register, R1, 10 } minus { pvk_register,
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R1, 5 } is { pvk_constant, <ignored>, 5 }.
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This means, for example, that we could subtract two stack
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addresses; they're both relative to the original SP. Since the
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frame pointer is set based on the SP, its value will be the
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original SP plus some constant (probably zero), so we can use its
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value just fine, too. */
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constant_last (&a, &b);
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/* We can subtract two constants. */
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if (a.kind == pvk_constant
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&& b.kind == pvk_constant)
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return pv_constant (a.k - b.k);
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/* We can subtract a constant from a register. */
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else if (a.kind == pvk_register
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&& b.kind == pvk_constant)
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return pv_register (a.reg, a.k - b.k);
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/* We can subtract a register from itself, yielding a constant. */
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else if (a.kind == pvk_register
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&& b.kind == pvk_register
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&& a.reg == b.reg)
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return pv_constant (a.k - b.k);
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/* We don't know how to subtract anything else. */
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else
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return pv_unknown ();
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}
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pv_t
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pv_logical_and (pv_t a, pv_t b)
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{
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constant_last (&a, &b);
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/* We can 'and' two constants. */
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if (a.kind == pvk_constant
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&& b.kind == pvk_constant)
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return pv_constant (a.k & b.k);
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/* We can 'and' anything with the constant zero. */
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else if (b.kind == pvk_constant
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&& b.k == 0)
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return pv_constant (0);
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/* We can 'and' anything with ~0. */
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else if (b.kind == pvk_constant
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&& b.k == ~ (CORE_ADDR) 0)
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return a;
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/* We can 'and' a register with itself. */
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else if (a.kind == pvk_register
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&& b.kind == pvk_register
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&& a.reg == b.reg
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&& a.k == b.k)
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return a;
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/* Otherwise, we don't know. */
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else
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return pv_unknown ();
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}
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/* Examining prologue values. */
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int
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pv_is_identical (pv_t a, pv_t b)
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{
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if (a.kind != b.kind)
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return 0;
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switch (a.kind)
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{
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case pvk_unknown:
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return 1;
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case pvk_constant:
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return (a.k == b.k);
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case pvk_register:
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return (a.reg == b.reg && a.k == b.k);
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default:
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gdb_assert_not_reached ("unexpected prologue value kind");
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}
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}
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int
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pv_is_constant (pv_t a)
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{
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return (a.kind == pvk_constant);
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}
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int
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pv_is_register (pv_t a, int r)
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{
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return (a.kind == pvk_register
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&& a.reg == r);
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}
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int
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pv_is_register_k (pv_t a, int r, CORE_ADDR k)
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{
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return (a.kind == pvk_register
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&& a.reg == r
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&& a.k == k);
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}
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enum pv_boolean
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pv_is_array_ref (pv_t addr, CORE_ADDR size,
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pv_t array_addr, CORE_ADDR array_len,
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CORE_ADDR elt_size,
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int *i)
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{
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/* Note that, since .k is a CORE_ADDR, and CORE_ADDR is unsigned, if
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addr is *before* the start of the array, then this isn't going to
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be negative... */
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pv_t offset = pv_subtract (addr, array_addr);
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if (offset.kind == pvk_constant)
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{
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/* This is a rather odd test. We want to know if the SIZE bytes
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at ADDR don't overlap the array at all, so you'd expect it to
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be an || expression: "if we're completely before || we're
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completely after". But with unsigned arithmetic, things are
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different: since it's a number circle, not a number line, the
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right values for offset.k are actually one contiguous range. */
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if (offset.k <= -size
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&& offset.k >= array_len * elt_size)
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return pv_definite_no;
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else if (offset.k % elt_size != 0
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|| size != elt_size)
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return pv_maybe;
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else
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{
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*i = offset.k / elt_size;
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return pv_definite_yes;
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}
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}
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else
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return pv_maybe;
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}
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/* Areas. */
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/* A particular value known to be stored in an area.
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Entries form a ring, sorted by unsigned offset from the area's base
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register's value. Since entries can straddle the wrap-around point,
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unsigned offsets form a circle, not a number line, so the list
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itself is structured the same way --- there is no inherent head.
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The entry with the lowest offset simply follows the entry with the
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highest offset. Entries may abut, but never overlap. The area's
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'entry' pointer points to an arbitrary node in the ring. */
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struct pv_area::area_entry
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{
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/* Links in the doubly-linked ring. */
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struct area_entry *prev, *next;
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/* Offset of this entry's address from the value of the base
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register. */
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CORE_ADDR offset;
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/* The size of this entry. Note that an entry may wrap around from
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the end of the address space to the beginning. */
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CORE_ADDR size;
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/* The value stored here. */
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pv_t value;
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};
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/* See prologue-value.h. */
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pv_area::pv_area (int base_reg, int addr_bit)
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: m_base_reg (base_reg),
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/* Remember that shift amounts equal to the type's width are
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undefined. */
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m_addr_mask (((((CORE_ADDR) 1 << (addr_bit - 1)) - 1) << 1) | 1),
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m_entry (nullptr)
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{
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}
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/* See prologue-value.h. */
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void
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pv_area::clear_entries ()
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{
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struct area_entry *e = m_entry;
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if (e)
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{
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/* This needs to be a do-while loop, in order to actually
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process the node being checked for in the terminating
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condition. */
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do
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{
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struct area_entry *next = e->next;
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xfree (e);
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e = next;
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}
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while (e != m_entry);
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m_entry = 0;
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}
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}
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pv_area::~pv_area ()
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{
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clear_entries ();
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}
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/* See prologue-value.h. */
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bool
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pv_area::store_would_trash (pv_t addr)
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{
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/* It may seem odd that pvk_constant appears here --- after all,
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that's the case where we know the most about the address! But
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pv_areas are always relative to a register, and we don't know the
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value of the register, so we can't compare entry addresses to
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constants. */
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return (addr.kind == pvk_unknown
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|| addr.kind == pvk_constant
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|| (addr.kind == pvk_register && addr.reg != m_base_reg));
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}
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/* See prologue-value.h. */
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struct pv_area::area_entry *
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pv_area::find_entry (CORE_ADDR offset)
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{
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struct area_entry *e = m_entry;
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if (! e)
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return 0;
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/* If the next entry would be better than the current one, then scan
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forward. Since we use '<' in this loop, it always terminates.
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Note that, even setting aside the addr_mask stuff, we must not
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simplify this, in high school algebra fashion, to
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(e->next->offset < e->offset), because of the way < interacts
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with wrap-around. We have to subtract offset from both sides to
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make sure both things we're comparing are on the same side of the
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discontinuity. */
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while (((e->next->offset - offset) & m_addr_mask)
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< ((e->offset - offset) & m_addr_mask))
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e = e->next;
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/* If the previous entry would be better than the current one, then
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scan backwards. */
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while (((e->prev->offset - offset) & m_addr_mask)
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< ((e->offset - offset) & m_addr_mask))
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e = e->prev;
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/* In case there's some locality to the searches, set the area's
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pointer to the entry we've found. */
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m_entry = e;
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return e;
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}
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/* See prologue-value.h. */
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int
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pv_area::overlaps (struct area_entry *entry, CORE_ADDR offset, CORE_ADDR size)
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{
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/* Think carefully about wrap-around before simplifying this. */
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return (((entry->offset - offset) & m_addr_mask) < size
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|| ((offset - entry->offset) & m_addr_mask) < entry->size);
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}
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/* See prologue-value.h. */
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void
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pv_area::store (pv_t addr, CORE_ADDR size, pv_t value)
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{
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/* Remove any (potentially) overlapping entries. */
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if (store_would_trash (addr))
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clear_entries ();
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else
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{
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CORE_ADDR offset = addr.k;
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struct area_entry *e = find_entry (offset);
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/* Delete all entries that we would overlap. */
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while (e && overlaps (e, offset, size))
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{
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struct area_entry *next = (e->next == e) ? 0 : e->next;
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e->prev->next = e->next;
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e->next->prev = e->prev;
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xfree (e);
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e = next;
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}
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/* Move the area's pointer to the next remaining entry. This
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will also zero the pointer if we've deleted all the entries. */
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m_entry = e;
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}
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/* Now, there are no entries overlapping us, and m_entry is
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either zero or pointing at the closest entry after us. We can
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just insert ourselves before that.
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But if we're storing an unknown value, don't bother --- that's
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the default. */
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if (value.kind == pvk_unknown)
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return;
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else
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{
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CORE_ADDR offset = addr.k;
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struct area_entry *e = XNEW (struct area_entry);
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e->offset = offset;
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e->size = size;
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e->value = value;
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if (m_entry)
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{
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e->prev = m_entry->prev;
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e->next = m_entry;
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e->prev->next = e->next->prev = e;
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}
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else
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{
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e->prev = e->next = e;
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m_entry = e;
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}
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}
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}
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/* See prologue-value.h. */
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pv_t
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pv_area::fetch (pv_t addr, CORE_ADDR size)
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{
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/* If we have no entries, or we can't decide how ADDR relates to the
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entries we do have, then the value is unknown. */
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if (! m_entry
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|| store_would_trash (addr))
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return pv_unknown ();
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else
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{
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CORE_ADDR offset = addr.k;
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struct area_entry *e = find_entry (offset);
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/* If this entry exactly matches what we're looking for, then
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we're set. Otherwise, say it's unknown. */
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if (e->offset == offset && e->size == size)
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return e->value;
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else
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return pv_unknown ();
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}
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}
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/* See prologue-value.h. */
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bool
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pv_area::find_reg (struct gdbarch *gdbarch, int reg, CORE_ADDR *offset_p)
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{
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struct area_entry *e = m_entry;
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if (e)
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do
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{
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if (e->value.kind == pvk_register
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&& e->value.reg == reg
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&& e->value.k == 0
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&& e->size == register_size (gdbarch, reg))
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{
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if (offset_p)
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*offset_p = e->offset;
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return true;
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}
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e = e->next;
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}
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while (e != m_entry);
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return false;
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}
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/* See prologue-value.h. */
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void
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pv_area::scan (void (*func) (void *closure,
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pv_t addr,
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CORE_ADDR size,
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pv_t value),
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void *closure)
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{
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struct area_entry *e = m_entry;
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pv_t addr;
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addr.kind = pvk_register;
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addr.reg = m_base_reg;
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if (e)
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do
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{
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addr.k = e->offset;
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func (closure, addr, e->size, e->value);
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e = e->next;
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}
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while (e != m_entry);
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}
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