[glibc] nptl: Export __libc_multiple_threads from libc as an internal symbol

[glibc] nptl: Export __libc_multiple_threads from libc as an internal symbol

[Florian Weimer]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=321789f61aa93c14390535aa3cf01846633cd022

commit 321789f61aa93c14390535aa3cf01846633cd022
Author: Florian Weimer <fweimer@redhat.com>
Date:   Mon May 10 10:31:41 2021 +0200

    nptl: Export __libc_multiple_threads from libc as an internal symbol
    
    This allows the elimination of the __libc_multiple_threads_ptr
    variable in libpthread and its initialization procedure.
    
    Tested-by: Carlos O'Donell <carlos@redhat.com>
    Reviewed-by: Carlos O'Donell <carlos@redhat.com>

Diff:
---
 nptl/Versions                           |  1 +
 nptl/allocatestack.c                    |  4 ++--
 nptl/libc_multiple_threads.c            |  3 ++-
 nptl/libc_pthread_init.c                | 11 -----------
 nptl/nptl-init.c                        | 10 +---------
 nptl/pthreadP.h                         |  6 +-----
 nptl/pthread_cancel.c                   |  2 +-
 sysdeps/unix/sysv/linux/single-thread.h |  6 +++++-
 8 files changed, 13 insertions(+), 30 deletions(-)

diff --git a/nptl/Versions b/nptl/Versions
index f950b77969..fb15a7e8eb 100644
--- a/nptl/Versions
+++ b/nptl/Versions
@@ -305,6 +305,7 @@ libc {
     __libc_cleanup_pop_restore;
     __libc_cleanup_push_defer;
     __libc_dl_error_tsd;
+    __libc_multiple_threads;
     __libc_pthread_init;
     __lll_clocklock_elision;
     __lll_lock_elision;
diff --git a/nptl/allocatestack.c b/nptl/allocatestack.c
index 8aaba088b1..059786192e 100644
--- a/nptl/allocatestack.c
+++ b/nptl/allocatestack.c
@@ -477,7 +477,7 @@ allocate_stack (const struct pthread_attr *attr, struct pthread **pdp,
       /* This is at least the second thread.  */
       pd->header.multiple_threads = 1;
 #ifndef TLS_MULTIPLE_THREADS_IN_TCB
-      __pthread_multiple_threads = *__libc_multiple_threads_ptr = 1;
+      __pthread_multiple_threads = __libc_multiple_threads = 1;
 #endif
 
 #ifdef NEED_DL_SYSINFO
@@ -598,7 +598,7 @@ allocate_stack (const struct pthread_attr *attr, struct pthread **pdp,
 	  /* This is at least the second thread.  */
 	  pd->header.multiple_threads = 1;
 #ifndef TLS_MULTIPLE_THREADS_IN_TCB
-	  __pthread_multiple_threads = *__libc_multiple_threads_ptr = 1;
+	  __pthread_multiple_threads = __libc_multiple_threads = 1;
 #endif
 
 #ifdef NEED_DL_SYSINFO
diff --git a/nptl/libc_multiple_threads.c b/nptl/libc_multiple_threads.c
index 60328023cd..a0e7932c26 100644
--- a/nptl/libc_multiple_threads.c
+++ b/nptl/libc_multiple_threads.c
@@ -23,6 +23,7 @@
 /* Variable set to a nonzero value either if more than one thread runs or ran,
    or if a single-threaded process is trying to cancel itself.  See
    nptl/descr.h for more context on the single-threaded process case.  */
-int __libc_multiple_threads attribute_hidden;
+int __libc_multiple_threads __attribute__ ((nocommon));
+libc_hidden_data_def (__libc_multiple_threads)
 # endif
 #endif
diff --git a/nptl/libc_pthread_init.c b/nptl/libc_pthread_init.c
index 397b83beb6..75f5d28ed6 100644
--- a/nptl/libc_pthread_init.c
+++ b/nptl/libc_pthread_init.c
@@ -27,20 +27,9 @@
 #include <sysdep.h>
 #include <ldsodefs.h>
 
-
-#ifdef TLS_MULTIPLE_THREADS_IN_TCB
 void
-#else
-extern int __libc_multiple_threads attribute_hidden;
-
-int *
-#endif
 __libc_pthread_init (void (*reclaim) (void))
 {
   /* Called by a child after fork.  */
   __register_atfork (NULL, NULL, reclaim, NULL);
-
-#ifndef TLS_MULTIPLE_THREADS_IN_TCB
-  return &__libc_multiple_threads;
-#endif
 }
diff --git a/nptl/nptl-init.c b/nptl/nptl-init.c
index 2724770533..2fb1117f3e 100644
--- a/nptl/nptl-init.c
+++ b/nptl/nptl-init.c
@@ -37,11 +37,6 @@
 #include <libc-pointer-arith.h>
 #include <pthread_mutex_conf.h>
 
-#ifndef TLS_MULTIPLE_THREADS_IN_TCB
-/* Pointer to the corresponding variable in libc.  */
-int *__libc_multiple_threads_ptr attribute_hidden;
-#endif
-
 /* Size and alignment of static TLS block.  */
 size_t __static_tls_size;
 size_t __static_tls_align_m1;
@@ -183,10 +178,7 @@ __pthread_initialize_minimal_internal (void)
 #endif
 
   /* Register the fork generation counter with the libc.  */
-#ifndef TLS_MULTIPLE_THREADS_IN_TCB
-  __libc_multiple_threads_ptr =
-#endif
-    __libc_pthread_init (__reclaim_stacks);
+  __libc_pthread_init (__reclaim_stacks);
 }
 strong_alias (__pthread_initialize_minimal_internal,
 	      __pthread_initialize_minimal)
diff --git a/nptl/pthreadP.h b/nptl/pthreadP.h
index 6b52ca158e..dd6d6c6342 100644
--- a/nptl/pthreadP.h
+++ b/nptl/pthreadP.h
@@ -368,17 +368,13 @@ extern unsigned long int __fork_generation attribute_hidden;
 extern unsigned long int *__fork_generation_pointer attribute_hidden;
 
 /* Register the generation counter in the libpthread with the libc.  */
-#ifdef TLS_MULTIPLE_THREADS_IN_TCB
 extern void __libc_pthread_init (void (*reclaim) (void));
-#else
-extern int *__libc_pthread_init (void (*reclaim) (void));
 
+#ifndef TLS_MULTIPLE_THREADS_IN_TCB
 /* Variable set to a nonzero value either if more than one thread runs or ran,
    or if a single-threaded process is trying to cancel itself.  See
    nptl/descr.h for more context on the single-threaded process case.  */
 extern int __pthread_multiple_threads attribute_hidden;
-/* Pointer to the corresponding variable in libc.  */
-extern int *__libc_multiple_threads_ptr attribute_hidden;
 #endif
 
 extern size_t __pthread_get_minstack (const pthread_attr_t *attr);
diff --git a/nptl/pthread_cancel.c b/nptl/pthread_cancel.c
index 060484cdc8..2cab8f0a34 100644
--- a/nptl/pthread_cancel.c
+++ b/nptl/pthread_cancel.c
@@ -90,7 +90,7 @@ __pthread_cancel (pthread_t th)
 	   points get executed.  */
 	THREAD_SETMEM (THREAD_SELF, header.multiple_threads, 1);
 #ifndef TLS_MULTIPLE_THREADS_IN_TCB
-	__pthread_multiple_threads = *__libc_multiple_threads_ptr = 1;
+	__pthread_multiple_threads = __libc_multiple_threads = 1;
 #endif
     }
   /* Mark the thread as canceled.  This has to be done
diff --git a/sysdeps/unix/sysv/linux/single-thread.h b/sysdeps/unix/sysv/linux/single-thread.h
index a28aaed04d..841f8c69d5 100644
--- a/sysdeps/unix/sysv/linux/single-thread.h
+++ b/sysdeps/unix/sysv/linux/single-thread.h
@@ -27,9 +27,13 @@
    The ABI might define SINGLE_THREAD_BY_GLOBAL to enable the single thread
    check to use global variables instead of the pthread_t field.  */
 
+#ifndef __ASSEMBLER__
+extern int __libc_multiple_threads;
+libc_hidden_proto (__libc_multiple_threads)
+#endif
+
 #ifdef SINGLE_THREAD_BY_GLOBAL
 # if IS_IN (libc)
-extern int __libc_multiple_threads;
 #  define SINGLE_THREAD_P \
   __glibc_likely (__libc_multiple_threads == 0)
 # elif IS_IN (libpthread)