mirror of https://gitee.com/openkylin/qemu.git
109 lines
3.5 KiB
C
109 lines
3.5 KiB
C
/*
|
|
* Variable page size handling
|
|
*
|
|
* Copyright (c) 2003 Fabrice Bellard
|
|
*
|
|
* This library is free software; you can redistribute it and/or
|
|
* modify it under the terms of the GNU Lesser General Public
|
|
* License as published by the Free Software Foundation; either
|
|
* version 2 of the License, or (at your option) any later version.
|
|
*
|
|
* This library is distributed in the hope that it will be useful,
|
|
* but WITHOUT ANY WARRANTY; without even the implied warranty of
|
|
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
|
|
* Lesser General Public License for more details.
|
|
*
|
|
* You should have received a copy of the GNU Lesser General Public
|
|
* License along with this library; if not, see <http://www.gnu.org/licenses/>.
|
|
*/
|
|
|
|
#include "qemu/osdep.h"
|
|
#include "qemu-common.h"
|
|
|
|
#define IN_EXEC_VARY 1
|
|
|
|
#include "exec/exec-all.h"
|
|
|
|
#ifdef TARGET_PAGE_BITS_VARY
|
|
# ifdef CONFIG_ATTRIBUTE_ALIAS
|
|
/*
|
|
* We want to declare the "target_page" variable as const, which tells
|
|
* the compiler that it can cache any value that it reads across calls.
|
|
* This avoids multiple assertions and multiple reads within any one user.
|
|
*
|
|
* This works because we finish initializing the data before we ever read
|
|
* from the "target_page" symbol.
|
|
*
|
|
* This also requires that we have a non-constant symbol by which we can
|
|
* perform the actual initialization, and which forces the data to be
|
|
* allocated within writable memory. Thus "init_target_page", and we use
|
|
* that symbol exclusively in the two functions that initialize this value.
|
|
*
|
|
* The "target_page" symbol is created as an alias of "init_target_page".
|
|
*/
|
|
static TargetPageBits init_target_page;
|
|
|
|
/*
|
|
* Note that this is *not* a redundant decl, this is the definition of
|
|
* the "target_page" symbol. The syntax for this definition requires
|
|
* the use of the extern keyword. This seems to be a GCC bug in
|
|
* either the syntax for the alias attribute or in -Wredundant-decls.
|
|
*
|
|
* See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91765
|
|
*/
|
|
# pragma GCC diagnostic push
|
|
# pragma GCC diagnostic ignored "-Wredundant-decls"
|
|
|
|
extern const TargetPageBits target_page
|
|
__attribute__((alias("init_target_page")));
|
|
|
|
# pragma GCC diagnostic pop
|
|
# else
|
|
/*
|
|
* When aliases are not supported then we force two different declarations,
|
|
* by way of suppressing the header declaration with IN_EXEC_VARY.
|
|
* We assume that on such an old compiler, LTO cannot be used, and so the
|
|
* compiler cannot not detect the mismatched declarations, and all is well.
|
|
*/
|
|
TargetPageBits target_page;
|
|
# define init_target_page target_page
|
|
# endif
|
|
#endif
|
|
|
|
bool set_preferred_target_page_bits(int bits)
|
|
{
|
|
/*
|
|
* The target page size is the lowest common denominator for all
|
|
* the CPUs in the system, so we can only make it smaller, never
|
|
* larger. And we can't make it smaller once we've committed to
|
|
* a particular size.
|
|
*/
|
|
#ifdef TARGET_PAGE_BITS_VARY
|
|
assert(bits >= TARGET_PAGE_BITS_MIN);
|
|
if (init_target_page.bits == 0 || init_target_page.bits > bits) {
|
|
if (init_target_page.decided) {
|
|
return false;
|
|
}
|
|
init_target_page.bits = bits;
|
|
}
|
|
#endif
|
|
return true;
|
|
}
|
|
|
|
void finalize_target_page_bits(void)
|
|
{
|
|
#ifdef TARGET_PAGE_BITS_VARY
|
|
if (init_target_page.bits == 0) {
|
|
init_target_page.bits = TARGET_PAGE_BITS_MIN;
|
|
}
|
|
init_target_page.mask = (target_long)-1 << init_target_page.bits;
|
|
init_target_page.decided = true;
|
|
|
|
/*
|
|
* For the benefit of an -flto build, prevent the compiler from
|
|
* hoisting a read from target_page before we finish initializing.
|
|
*/
|
|
barrier();
|
|
#endif
|
|
}
|