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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>
This commit is contained in:
Adhemerval Zanella 2022-06-07 11:11:03 -03:00
parent 5b41b2659d
commit baf2a265c7
7 changed files with 42 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
elf/libc_early_init.c
View File

@ -38,7 +38,7 @@ __libc_early_init (_Bool initial)
__libc_single_threaded = initial;
#ifdef SHARED
__libc_initial = initial;
__libc_single_threaded_internal = __libc_initial = initial;
#endif
__pthread_early_init ();

22
include/libc-symbols.h
View File

@ -534,11 +534,15 @@ for linking")
__attribute__ ((visibility ("hidden"), ##attrs))
# define hidden_proto(name, attrs...) \
__hidden_proto (name, , __GI_##name, ##attrs)
# define hidden_proto_alias(name, alias, attrs...) \
__hidden_proto_alias (name, , alias, ##attrs)
# define hidden_tls_proto(name, attrs...) \
__hidden_proto (name, __thread, __GI_##name, ##attrs)
# define __hidden_proto(name, thread, internal, attrs...) \
extern thread __typeof (name) name __asm__ (__hidden_asmname (#internal)) \
__hidden_proto_hiddenattr (attrs);
# define __hidden_proto_alias(name, thread, internal, attrs...) \
extern thread __typeof (name) internal __hidden_proto_hiddenattr (attrs);
# define __hidden_asmname(name) \
__hidden_asmname1 (__USER_LABEL_PREFIX__, name)
# define __hidden_asmname1(prefix, name) __hidden_asmname2(prefix, name)
@ -554,7 +558,10 @@ for linking")
# define hidden_ver(local, name) __hidden_ver1(local, __GI_##name, name);
# define hidden_data_ver(local, name) hidden_ver(local, name)
# define hidden_def(name) __hidden_ver1(__GI_##name, name, name);
# define hidden_def_alias(name, internal) \
strong_alias (name, internal)
# define hidden_data_def(name) hidden_def(name)
# define hidden_data_def_alias(name, alias) hidden_def_alias(name, alias)
# define hidden_tls_def(name) \
__hidden_ver2 (__thread, __GI_##name, name, name);
# define hidden_weak(name) \
@ -581,9 +588,11 @@ for linking")
hidden_proto doesn't make sense for assembly but the equivalent
is to call via the HIDDEN_JUMPTARGET macro instead of JUMPTARGET. */
# define hidden_def(name) strong_alias (name, __GI_##name)
# define hidden_def_alias(name, alias) strong_alias (name, alias)
# define hidden_weak(name) hidden_def (name)
# define hidden_ver(local, name) strong_alias (local, __GI_##name)
# define hidden_data_def(name) strong_data_alias (name, __GI_##name)
# define hidden_data_def_alias(name, alias) strong_data_alias (name, alias)
# define hidden_tls_def(name) hidden_data_def (name)
# define hidden_data_weak(name) hidden_data_def (name)
# define hidden_data_ver(local, name) strong_data_alias (local, __GI_##name)
@ -598,12 +607,17 @@ for linking")
__attribute__ ((visibility ("hidden"), ##attrs))
# define hidden_proto(name, attrs...) \
__hidden_proto (name, , name, ##attrs)
# define hidden_proto_alias(name, alias, attrs...) \
__hidden_proto_alias (name, , alias, ##attrs)
# define hidden_tls_proto(name, attrs...) \
__hidden_proto (name, __thread, name, ##attrs)
# define __hidden_proto(name, thread, internal, attrs...) \
extern thread __typeof (name) name __hidden_proto_hiddenattr (attrs);
# define __hidden_proto_alias(name, thread, internal, attrs...) \
extern thread __typeof (name) internal __hidden_proto_hiddenattr (attrs);
# else
# define hidden_proto(name, attrs...)
# define hidden_proto_alias(name, alias, attrs...)
# define hidden_tls_proto(name, attrs...)
# endif
# else
@ -611,9 +625,11 @@ for linking")
# endif /* Not __ASSEMBLER__ */
# define hidden_weak(name)
# define hidden_def(name)
# define hidden_def_alias(name, alias)
# define hidden_ver(local, name)
# define hidden_data_weak(name)
# define hidden_data_def(name)
# define hidden_data_def_alias(name, alias)
# define hidden_tls_def(name)
# define hidden_data_ver(local, name)
# define hidden_nolink(name, lib, version)
@ -621,22 +637,28 @@ for linking")
#if IS_IN (libc)
# define libc_hidden_proto(name, attrs...) hidden_proto (name, ##attrs)
# define libc_hidden_proto_alias(name, alias, attrs...) \
hidden_proto_alias (name, alias, ##attrs)
# define libc_hidden_tls_proto(name, attrs...) hidden_tls_proto (name, ##attrs)
# define libc_hidden_def(name) hidden_def (name)
# define libc_hidden_def_alias(name, alias) hidden_def_alias (name, alias)
# define libc_hidden_weak(name) hidden_weak (name)
# define libc_hidden_nolink_sunrpc(name, version) hidden_nolink (name, libc, version)
# define libc_hidden_ver(local, name) hidden_ver (local, name)
# define libc_hidden_data_def(name) hidden_data_def (name)
# define libc_hidden_data_def_alias(name, alias) hidden_data_def_alias (name, alias)
# define libc_hidden_tls_def(name) hidden_tls_def (name)
# define libc_hidden_data_weak(name) hidden_data_weak (name)
# define libc_hidden_data_ver(local, name) hidden_data_ver (local, name)
#else
# define libc_hidden_proto(name, attrs...)
# define libc_hidden_proto_alias(name, alias, attrs...)
# define libc_hidden_tls_proto(name, attrs...)
# define libc_hidden_def(name)
# define libc_hidden_weak(name)
# define libc_hidden_ver(local, name)
# define libc_hidden_data_def(name)
# define libc_hidden_data_def_alias(name, alias)
# define libc_hidden_tls_def(name)
# define libc_hidden_data_weak(name)
# define libc_hidden_data_ver(local, name)

11
include/sys/single_threaded.h
View File

@ -1 +1,12 @@
#include <misc/sys/single_threaded.h>
#ifndef _ISOMAC
libc_hidden_proto_alias (__libc_single_threaded,
__libc_single_threaded_internal);
#if !defined SHARED || !IS_IN(libc)
# define __libc_single_threaded_internal __libc_single_threaded
#endif
#endif

2
misc/single_threaded.c
View File

@ -25,3 +25,5 @@ char __libc_single_threaded;
#else
char __libc_single_threaded = 1;
#endif
libc_hidden_data_def_alias (__libc_single_threaded,
__libc_single_threaded_internal)

5
nptl/pthread_create.c
View File

@ -624,9 +624,12 @@ __pthread_create_2_1 (pthread_t *newthread, const pthread_attr_t *attr,
/* Avoid a data race in the multi-threaded case, and call the
deferred initialization only once. */
if (__libc_single_threaded)
if (__libc_single_threaded_internal)
{
late_init ();
__libc_single_threaded_internal = 0;
/* __libc_single_threaded can be accessed through copy relocations, so
it requires to update the external copy. */
__libc_single_threaded = 0;
}

2
posix/fork.c
View File

@ -45,7 +45,7 @@ __libc_fork (void)
requirement for fork (Austin Group tracker issue #62) this is
best effort to make is async-signal-safe at least for single-thread
case. */
bool multiple_threads = __libc_single_threaded == 0;
bool multiple_threads = __libc_single_threaded_internal == 0;
uint64_t lastrun;
lastrun = __run_prefork_handlers (multiple_threads);

2
sysdeps/nptl/setxid.h
View File

@ -29,7 +29,7 @@
#define INLINE_SETXID_SYSCALL(name, nr, args...) \
({ \
int __result; \
if (!__libc_single_threaded) \
if (!__libc_single_threaded_internal) \
{ \
struct xid_command __cmd; \
__cmd.syscall_no = __NR_##name; \