mirror of https://gitee.com/openkylin/qemu.git
109 lines
3.5 KiB
C
109 lines
3.5 KiB
C
/*
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* Variable page size handling
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*
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* Copyright (c) 2003 Fabrice Bellard
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*
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* This library is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Lesser General Public
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* License as published by the Free Software Foundation; either
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* version 2.1 of the License, or (at your option) any later version.
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*
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* This library 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 GNU
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* Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public
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* License along with this library; if not, see <http://www.gnu.org/licenses/>.
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*/
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#include "qemu/osdep.h"
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#include "qemu-common.h"
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#define IN_EXEC_VARY 1
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#include "exec/exec-all.h"
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#ifdef TARGET_PAGE_BITS_VARY
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# ifdef CONFIG_ATTRIBUTE_ALIAS
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/*
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* We want to declare the "target_page" variable as const, which tells
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* the compiler that it can cache any value that it reads across calls.
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* This avoids multiple assertions and multiple reads within any one user.
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*
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* This works because we finish initializing the data before we ever read
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* from the "target_page" symbol.
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*
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* This also requires that we have a non-constant symbol by which we can
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* perform the actual initialization, and which forces the data to be
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* allocated within writable memory. Thus "init_target_page", and we use
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* that symbol exclusively in the two functions that initialize this value.
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*
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* The "target_page" symbol is created as an alias of "init_target_page".
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*/
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static TargetPageBits init_target_page;
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/*
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* Note that this is *not* a redundant decl, this is the definition of
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* the "target_page" symbol. The syntax for this definition requires
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* the use of the extern keyword. This seems to be a GCC bug in
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* either the syntax for the alias attribute or in -Wredundant-decls.
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*
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* See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91765
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*/
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# pragma GCC diagnostic push
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# pragma GCC diagnostic ignored "-Wredundant-decls"
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extern const TargetPageBits target_page
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__attribute__((alias("init_target_page")));
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# pragma GCC diagnostic pop
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# else
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/*
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* When aliases are not supported then we force two different declarations,
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* by way of suppressing the header declaration with IN_EXEC_VARY.
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* We assume that on such an old compiler, LTO cannot be used, and so the
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* compiler cannot not detect the mismatched declarations, and all is well.
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*/
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TargetPageBits target_page;
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# define init_target_page target_page
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# endif
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#endif
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bool set_preferred_target_page_bits(int bits)
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{
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/*
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* The target page size is the lowest common denominator for all
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* the CPUs in the system, so we can only make it smaller, never
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* larger. And we can't make it smaller once we've committed to
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* a particular size.
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*/
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#ifdef TARGET_PAGE_BITS_VARY
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assert(bits >= TARGET_PAGE_BITS_MIN);
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if (init_target_page.bits == 0 || init_target_page.bits > bits) {
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if (init_target_page.decided) {
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return false;
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}
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init_target_page.bits = bits;
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}
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#endif
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return true;
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}
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void finalize_target_page_bits(void)
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{
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#ifdef TARGET_PAGE_BITS_VARY
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if (init_target_page.bits == 0) {
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init_target_page.bits = TARGET_PAGE_BITS_MIN;
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}
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init_target_page.mask = (target_long)-1 << init_target_page.bits;
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init_target_page.decided = true;
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/*
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* For the benefit of an -flto build, prevent the compiler from
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* hoisting a read from target_page before we finish initializing.
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*/
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barrier();
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#endif
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}
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