/* * 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 }