diff --git a/MAINTAINERS b/MAINTAINERS index ed68de3cec..10ed6d7624 100644 --- a/MAINTAINERS +++ b/MAINTAINERS @@ -118,6 +118,7 @@ S: Maintained F: softmmu/cpus.c F: cpus-common.c F: page-vary.c +F: page-vary-common.c F: accel/tcg/ F: accel/stubs/tcg-stub.c F: util/cacheinfo.c diff --git a/configure b/configure index 61872096a8..edf9dc8985 100755 --- a/configure +++ b/configure @@ -4889,21 +4889,6 @@ if test "$plugins" = "yes" && "for this purpose. You can't build with --static." fi -######################################## -# See if __attribute__((alias)) is supported. -# This false for Xcode 9, but has been remedied for Xcode 10. -# Unfortunately, travis uses Xcode 9 by default. - -attralias=no -cat > $TMPC << EOF -int x = 1; -extern const int y __attribute__((alias("x"))); -int main(void) { return 0; } -EOF -if compile_prog "" "" ; then - attralias=yes -fi - ######################################## # check if getauxval is available. @@ -5935,10 +5920,6 @@ if test "$atomic64" = "yes" ; then echo "CONFIG_ATOMIC64=y" >> $config_host_mak fi -if test "$attralias" = "yes" ; then - echo "CONFIG_ATTRIBUTE_ALIAS=y" >> $config_host_mak -fi - if test "$getauxval" = "yes" ; then echo "CONFIG_GETAUXVAL=y" >> $config_host_mak fi diff --git a/include/exec/cpu-all.h b/include/exec/cpu-all.h index b0a422c7b6..d76b0b9e02 100644 --- a/include/exec/cpu-all.h +++ b/include/exec/cpu-all.h @@ -216,11 +216,7 @@ static inline void stl_phys_notdirty(AddressSpace *as, hwaddr addr, uint32_t val #ifdef TARGET_PAGE_BITS_VARY # include "exec/page-vary.h" -#if defined(CONFIG_ATTRIBUTE_ALIAS) || !defined(IN_EXEC_VARY) extern const TargetPageBits target_page; -#else -extern TargetPageBits target_page; -#endif #ifdef CONFIG_DEBUG_TCG #define TARGET_PAGE_BITS ({ assert(target_page.decided); target_page.bits; }) #define TARGET_PAGE_MASK ({ assert(target_page.decided); \ diff --git a/include/exec/page-vary.h b/include/exec/page-vary.h index 799d6310d6..c22a7a742e 100644 --- a/include/exec/page-vary.h +++ b/include/exec/page-vary.h @@ -26,4 +26,9 @@ typedef struct { uint64_t mask; } TargetPageBits; +#ifdef IN_PAGE_VARY +extern bool set_preferred_target_page_bits_common(int bits); +extern void finalize_target_page_bits_common(int min); +#endif + #endif /* EXEC_PAGE_VARY_H */ diff --git a/meson.build b/meson.build index f0dd8aa089..c6f4b0cf5e 100644 --- a/meson.build +++ b/meson.build @@ -1944,6 +1944,24 @@ specific_ss.add(when: 'CONFIG_TCG', if_true: files( )) specific_ss.add(when: 'CONFIG_TCG_INTERPRETER', if_true: files('tcg/tci.c')) +# Work around a gcc bug/misfeature wherein constant propagation looks +# through an alias: +# https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99696 +# to guess that a const variable is always zero. Without lto, this is +# impossible, as the alias is restricted to page-vary-common.c. Indeed, +# without lto, not even the alias is required -- we simply use different +# declarations in different compilation units. +pagevary = files('page-vary-common.c') +if get_option('b_lto') + pagevary_flags = ['-fno-lto'] + if get_option('cfi') + pagevary_flags += '-fno-sanitize=cfi-icall' + endif + pagevary = static_library('page-vary-common', sources: pagevary, + c_args: pagevary_flags) + pagevary = declare_dependency(link_with: pagevary) +endif +common_ss.add(pagevary) specific_ss.add(files('page-vary.c')) subdir('backends') diff --git a/page-vary-common.c b/page-vary-common.c new file mode 100644 index 0000000000..9175556498 --- /dev/null +++ b/page-vary-common.c @@ -0,0 +1,54 @@ +/* + * Variable page size handling -- target independent 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 . + */ + +#define IN_PAGE_VARY 1 + +#include "qemu/osdep.h" +#include "qemu-common.h" +#include "exec/page-vary.h" + +/* WARNING: This file must *not* be complied with -flto. */ + +TargetPageBits target_page; + +bool set_preferred_target_page_bits_common(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. + */ + if (target_page.bits == 0 || target_page.bits > bits) { + if (target_page.decided) { + return false; + } + target_page.bits = bits; + } + return true; +} + +void finalize_target_page_bits_common(int min) +{ + if (target_page.bits == 0) { + target_page.bits = min; + } + target_page.mask = -1ull << target_page.bits; + target_page.decided = true; +} diff --git a/page-vary.c b/page-vary.c index 344f9fcf76..057c7f1815 100644 --- a/page-vary.c +++ b/page-vary.c @@ -17,92 +17,25 @@ * License along with this library; if not, see . */ +#define IN_PAGE_VARY 1 + #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 set_preferred_target_page_bits_common(bits); +#else return true; +#endif } 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(); + finalize_target_page_bits_common(TARGET_PAGE_BITS_MIN); #endif }