glibc/misc/single_threaded.c

/* Support for single-thread optimizations.  Statically linked version.
   Copyright (C) 2020-2023 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

   The GNU C 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.

   The GNU C 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 the GNU C Library; if not, see
   <https://www.gnu.org/licenses/>.  */

#include <sys/single_threaded.h>

/* In dynamically linked programs, this variable is initialized in
   __libc_early_init (as false for inner libcs).  */
#ifdef SHARED
char __libc_single_threaded;
#else
char __libc_single_threaded = 1;
#endif
libc_hidden_data_def_alias (__libc_single_threaded,
			    __libc_single_threaded_internal)
Add the __libc_single_threaded variable The variable is placed in libc.so, and it can be true only in an outer libc, not libcs loaded via dlmopen or static dlopen. Since thread creation from inner namespaces does not work, pthread_create can update __libc_single_threaded directly. Using __libc_early_init and its initial flag, implementation of this variable is very straightforward. A future version may reset the flag during fork (but not in an inner namespace), or after joining all threads except one. Reviewed-by: DJ Delorie <dj@redhat.com> 2020-05-20 13:40:35 +00:00			`/* Support for single-thread optimizations. Statically linked version.`
Update copyright dates with scripts/update-copyrights 2023-01-06 21:08:04 +00:00			`Copyright (C) 2020-2023 Free Software Foundation, Inc.`
Add the __libc_single_threaded variable The variable is placed in libc.so, and it can be true only in an outer libc, not libcs loaded via dlmopen or static dlopen. Since thread creation from inner namespaces does not work, pthread_create can update __libc_single_threaded directly. Using __libc_early_init and its initial flag, implementation of this variable is very straightforward. A future version may reset the flag during fork (but not in an inner namespace), or after joining all threads except one. Reviewed-by: DJ Delorie <dj@redhat.com> 2020-05-20 13:40:35 +00:00			`This file is part of the GNU C Library.`

			`The GNU C 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.`

			`The GNU C 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 the GNU C Library; if not, see`
			`<https://www.gnu.org/licenses/>. */`

			`#include <sys/single_threaded.h>`

			`/* In dynamically linked programs, this variable is initialized in`
			`__libc_early_init (as false for inner libcs). */`
			`#ifdef SHARED`
			`char __libc_single_threaded;`
			`#else`
			`char __libc_single_threaded = 1;`
			`#endif`
misc: Optimize internal usage of __libc_single_threaded By adding an internal alias to avoid the GOT indirection. On some architecture, __libc_single_thread may be accessed through copy relocations and thus it requires to update also the copies default copy. This is done by adding a new internal macro, libc_hidden_data_{proto,def}, which has an addition argument that specifies the alias name (instead of default __GI_ one). Checked on x86_64-linux-gnu and i686-linux-gnu. Reviewed-by: Fangrui Song <maskray@google.com> 2022-06-07 14:11:03 +00:00			`libc_hidden_data_def_alias (__libc_single_threaded,`
			`__libc_single_threaded_internal)`