[PATCH v3 1/4] misc: Optimize internal usage of __libc_single_threaded
Fangrui Song
maskray@google.com
Thu Jun 23 04:15:43 GMT 2022
On 2022-06-21, Adhemerval Zanella wrote:
>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.
>---
> elf/libc_early_init.c | 2 +-
> include/libc-symbols.h | 22 ++++++++++++++++++++++
> include/sys/single_threaded.h | 11 +++++++++++
> misc/single_threaded.c | 2 ++
> nptl/pthread_create.c | 5 ++++-
> posix/fork.c | 2 +-
> sysdeps/nptl/setxid.h | 2 +-
> 7 files changed, 42 insertions(+), 4 deletions(-)
>
>diff --git a/elf/libc_early_init.c b/elf/libc_early_init.c
>index 3c4a19cf6b..affc46fefc 100644
>--- a/elf/libc_early_init.c
>+++ b/elf/libc_early_init.c
>@@ -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 ();
>diff --git a/include/libc-symbols.h b/include/libc-symbols.h
>index 4bb3d8c7ba..4fde839471 100644
>--- a/include/libc-symbols.h
>+++ b/include/libc-symbols.h
>@@ -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)
include/libc-symbols.h is very difficult to read.
I can only use the preprocessed output to understand that this patch
works as intended.
I wish that we can simplify the file a bit :-)
>diff --git a/include/sys/single_threaded.h b/include/sys/single_threaded.h
>index 18f6972482..2015742be0 100644
>--- a/include/sys/single_threaded.h
>+++ b/include/sys/single_threaded.h
>@@ -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
Does this file need a header guard now?
>diff --git a/misc/single_threaded.c b/misc/single_threaded.c
>index 96ada9137b..9b0746a69c 100644
>--- a/misc/single_threaded.c
>+++ b/misc/single_threaded.c
>@@ -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)
>diff --git a/nptl/pthread_create.c b/nptl/pthread_create.c
>index e7a099acb7..5b98e053d6 100644
>--- a/nptl/pthread_create.c
>+++ b/nptl/pthread_create.c
>@@ -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;
> }
LGTM. I verify that __libc_single_threaded has a GLOB_DAT.
Reviewed-by: Fangrui Song <maskray@google.com>
>diff --git a/posix/fork.c b/posix/fork.c
>index e1be3422ea..987916a175 100644
>--- a/posix/fork.c
>+++ b/posix/fork.c
>@@ -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);
>diff --git a/sysdeps/nptl/setxid.h b/sysdeps/nptl/setxid.h
>index b821d6bc07..b87cad7b18 100644
>--- a/sysdeps/nptl/setxid.h
>+++ b/sysdeps/nptl/setxid.h
>@@ -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; \
>--
>2.34.1
>
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