From 6670d4d0e38249323df755a92ffdf04f2c6b7894 Mon Sep 17 00:00:00 2001 From: Richard Henderson Date: Mon, 22 Mar 2021 12:24:24 +0100 Subject: exec: Rename exec-vary.c as page-vary.c MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit exec-vary.c is about variable page size handling, rename it page-vary.c. Currently this file is target specific (built once for each target), comment this. Signed-off-by: Philippe Mathieu-Daudé Message-Id: <20210322112427.4045204-2-f4bug@amsat.org> [rth: Update MAINTAINERS] Signed-off-by: Richard Henderson --- page-vary.c | 108 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 108 insertions(+) create mode 100644 page-vary.c (limited to 'page-vary.c') diff --git a/page-vary.c b/page-vary.c new file mode 100644 index 0000000000..344f9fcf76 --- /dev/null +++ b/page-vary.c @@ -0,0 +1,108 @@ +/* + * Variable page size handling -- target specific part. + * + * 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 2.1 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 . + */ + +#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 +} -- cgit v1.2.3