This patch is based on the below upstream commit.

File deletions were altered to reflect file renames.

commit f50277c19df0937ea9691ab7e7c642ecd3ed3d94

Author: Torvald Riegel <triegel@redhat.com>

Date:   Sun Oct 19 21:59:26 2014 +0200

    pthread_once: Add fast path and remove x86 variants.

diff --git a/nptl/pthread_once.c b/nptl/pthread_once.c

index 595bd7e298003e00..2afb79c01fe0a61e 100644

--- a/nptl/pthread_once.c

+++ b/nptl/pthread_once.c

@@ -58,11 +58,13 @@ clear_once_control (void *arg)

    initialization is interrupted, we then fork 2^30 times (30 bits of

    once_control are used for the fork generation), and try to initialize

    again, we can deadlock because we can't distinguish the in-progress and

-   interrupted cases anymore.  */

-int

-__pthread_once (once_control, init_routine)

-     pthread_once_t *once_control;

-     void (*init_routine) (void);

+   interrupted cases anymore.

+   XXX: We split out this slow path because current compilers do not generate

+   as efficient code when the fast path in __pthread_once below is not in a

+   separate function.  */

+static int

+__attribute__ ((noinline))

+__pthread_once_slow (pthread_once_t *once_control, void (*init_routine) (void))

 {

   while (1)

     {

@@ -72,7 +74,7 @@ __pthread_once (once_control, init_routine)

          signals that initialization has finished, we need to see any

          data modifications done during initialization.  */

       val = *once_control;

-      atomic_read_barrier();

+      atomic_read_barrier ();

       do

 	{

 	  /* Check if the initialization has already been done.  */

@@ -130,5 +132,18 @@ __pthread_once (once_control, init_routine)

   return 0;

 }

+

+int

+__pthread_once (pthread_once_t *once_control, void (*init_routine) (void))

+{

+  /* Fast path.  See __pthread_once_slow.  */

+  int val;

+  val = *once_control;

+  atomic_read_barrier ();

+  if (__glibc_likely ((val & __PTHREAD_ONCE_DONE) != 0))

+    return 0;

+  else

+    return __pthread_once_slow (once_control, init_routine);

+}

 weak_alias (__pthread_once, pthread_once)

 hidden_def (__pthread_once)

diff --git a/nptl/sysdeps/unix/sysv/linux/i386/pthread_once.S b/nptl/sysdeps/unix/sysv/linux/i386/pthread_once.S

deleted file mode 100644

index ca3b860a7f6f95ae..0000000000000000

--- a/nptl/sysdeps/unix/sysv/linux/i386/pthread_once.S

+++ /dev/null

@@ -1,178 +0,0 @@

-/* Copyright (C) 2002-2012 Free Software Foundation, Inc.

-   This file is part of the GNU C Library.

-   Contributed by Ulrich Drepper <drepper@redhat.com>, 2002.

-

-   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

-   <http://www.gnu.org/licenses/>.  */

-

-#include <unwindbuf.h>

-#include <sysdep.h>

-#include <kernel-features.h>

-#include <lowlevellock.h>

-

-

-	.comm	__fork_generation, 4, 4

-

-	.text

-

-

-	.globl	__pthread_once

-	.type	__pthread_once,@function

-	.align	16

-	cfi_startproc

-__pthread_once:

-	movl	4(%esp), %ecx

-	testl	$2, (%ecx)

-	jz	1f

-	xorl	%eax, %eax

-	ret

-

-1:	pushl	%ebx

-	cfi_adjust_cfa_offset (4)

-	cfi_rel_offset (3, 0)

-	pushl	%esi

-	cfi_adjust_cfa_offset (4)

-	cfi_rel_offset (6, 0)

-	movl	%ecx, %ebx

-	xorl	%esi, %esi

-

-	/* Not yet initialized or initialization in progress.

-	   Get the fork generation counter now.  */

-6:	movl	(%ebx), %eax

-#ifdef PIC

-	LOAD_PIC_REG(cx)

-#endif

-

-5:	movl	%eax, %edx

-

-	testl	$2, %eax

-	jnz	4f

-

-	andl	$3, %edx

-#ifdef PIC

-	orl	__fork_generation@GOTOFF(%ecx), %edx

-#else

-	orl	__fork_generation, %edx

-#endif

-	orl	$1, %edx

-

-	LOCK

-	cmpxchgl %edx, (%ebx)

-	jnz	5b

-

-	/* Check whether another thread already runs the initializer.  */

-	testl	$1, %eax

-	jz	3f	/* No -> do it.  */

-

-	/* Check whether the initializer execution was interrupted

-	   by a fork.  */

-	xorl	%edx, %eax

-	testl	$0xfffffffc, %eax

-	jnz	3f	/* Different for generation -> run initializer.  */

-

-	/* Somebody else got here first.  Wait.  */

-#ifdef __ASSUME_PRIVATE_FUTEX

-	movl	$FUTEX_WAIT|FUTEX_PRIVATE_FLAG, %ecx

-#else

-# if FUTEX_WAIT == 0

-	movl	%gs:PRIVATE_FUTEX, %ecx

-# else

-	movl	$FUTEX_WAIT, %ecx

-	orl	%gs:PRIVATE_FUTEX, %ecx

-# endif

-#endif

-	movl	$SYS_futex, %eax

-	ENTER_KERNEL

-	jmp	6b

-

-3:	/* Call the initializer function after setting up the

-	   cancellation handler.  Note that it is not possible here

-	   to use the unwind-based cleanup handling.  This would require

-	   that the user-provided function and all the code it calls

-	   is compiled with exceptions.  Unfortunately this cannot be

-	   guaranteed.  */

-	subl	$UNWINDBUFSIZE+8, %esp

-	cfi_adjust_cfa_offset (UNWINDBUFSIZE+8)

-	movl	%ecx, %ebx		/* PIC register value.  */

-

-	leal	8+UWJMPBUF(%esp), %eax

-	movl	$0, 4(%esp)

-	movl	%eax, (%esp)

-	call	__sigsetjmp@PLT

-	testl	%eax, %eax

-	jne	7f

-

-	leal	8(%esp), %eax

-	call	HIDDEN_JUMPTARGET(__pthread_register_cancel)

-

-	/* Call the user-provided initialization function.  */

-	call	*24+UNWINDBUFSIZE(%esp)

-

-	/* Pop the cleanup handler.  */

-	leal	8(%esp), %eax

-	call	HIDDEN_JUMPTARGET(__pthread_unregister_cancel)

-	addl	$UNWINDBUFSIZE+8, %esp

-	cfi_adjust_cfa_offset (-UNWINDBUFSIZE-8)

-

-	/* Sucessful run of the initializer.  Signal that we are done.  */

-	movl	12(%esp), %ebx

-	LOCK

-	addl	$1, (%ebx)

-

-	/* Wake up all other threads.  */

-	movl	$0x7fffffff, %edx

-#ifdef __ASSUME_PRIVATE_FUTEX

-	movl	$FUTEX_WAKE|FUTEX_PRIVATE_FLAG, %ecx

-#else

-	movl	$FUTEX_WAKE, %ecx

-	orl	%gs:PRIVATE_FUTEX, %ecx

-#endif

-	movl	$SYS_futex, %eax

-	ENTER_KERNEL

-

-4:	popl	%esi

-	cfi_adjust_cfa_offset (-4)

-	cfi_restore (6)

-	popl	%ebx

-	cfi_adjust_cfa_offset (-4)

-	cfi_restore (3)

-	xorl	%eax, %eax

-	ret

-

-7:	/* __sigsetjmp returned for the second time.  */

-	movl	20+UNWINDBUFSIZE(%esp), %ebx

-	cfi_adjust_cfa_offset (UNWINDBUFSIZE+16)

-	cfi_offset (3, -8)

-	cfi_offset (6, -12)

-	movl	$0, (%ebx)

-

-	movl	$0x7fffffff, %edx

-#ifdef __ASSUME_PRIVATE_FUTEX

-	movl	$FUTEX_WAKE|FUTEX_PRIVATE_FLAG, %ecx

-#else

-	movl	$FUTEX_WAKE, %ecx

-	orl	%gs:PRIVATE_FUTEX, %ecx

-#endif

-	movl	$SYS_futex, %eax

-	ENTER_KERNEL

-

-	leal	8(%esp), %eax

-	call	HIDDEN_JUMPTARGET (__pthread_unwind_next)

-	/* NOTREACHED */

-	hlt

-	cfi_endproc

-	.size	__pthread_once,.-__pthread_once

-

-hidden_def (__pthread_once)

-strong_alias (__pthread_once, pthread_once)

diff --git a/nptl/sysdeps/unix/sysv/linux/x86_64/pthread_once.S b/nptl/sysdeps/unix/sysv/linux/x86_64/pthread_once.S

deleted file mode 100644

index 7f5c0810fa16b987..0000000000000000

--- a/nptl/sysdeps/unix/sysv/linux/x86_64/pthread_once.S

+++ /dev/null

@@ -1,193 +0,0 @@

-/* Copyright (C) 2002-2012 Free Software Foundation, Inc.

-   This file is part of the GNU C Library.

-   Contributed by Ulrich Drepper <drepper@redhat.com>, 2002.

-

-   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

-   <http://www.gnu.org/licenses/>.  */

-

-#include <sysdep.h>

-#include <kernel-features.h>

-#include <tcb-offsets.h>

-#include <lowlevellock.h>

-

-

-	.comm	__fork_generation, 4, 4

-

-	.text

-

-

-	.globl	__pthread_once

-	.type	__pthread_once,@function

-	.align	16

-__pthread_once:

-.LSTARTCODE:

-	cfi_startproc

-#ifdef SHARED

-	cfi_personality(DW_EH_PE_pcrel | DW_EH_PE_sdata4 | DW_EH_PE_indirect,

-			DW.ref.__gcc_personality_v0)

-	cfi_lsda(DW_EH_PE_pcrel | DW_EH_PE_sdata4, .LexceptSTART)

-#else

-	cfi_personality(DW_EH_PE_udata4, __gcc_personality_v0)

-	cfi_lsda(DW_EH_PE_udata4, .LexceptSTART)

-#endif

-	testl	$2, (%rdi)

-	jz	1f

-	xorl	%eax, %eax

-	retq

-

-	/* Preserve the function pointer.  */

-1:	pushq	%rsi

-	cfi_adjust_cfa_offset(8)

-	xorq	%r10, %r10

-

-	/* Not yet initialized or initialization in progress.

-	   Get the fork generation counter now.  */

-6:	movl	(%rdi), %eax

-

-5:	movl	%eax, %edx

-

-	testl	$2, %eax

-	jnz	4f

-

-	andl	$3, %edx

-	orl	__fork_generation(%rip), %edx

-	orl	$1, %edx

-

-	LOCK

-	cmpxchgl %edx, (%rdi)

-	jnz	5b

-

-	/* Check whether another thread already runs the initializer.  */

-	testl	$1, %eax

-	jz	3f	/* No -> do it.  */

-

-	/* Check whether the initializer execution was interrupted

-	   by a fork.  */

-	xorl	%edx, %eax

-	testl	$0xfffffffc, %eax

-	jnz	3f	/* Different for generation -> run initializer.  */

-

-	/* Somebody else got here first.  Wait.  */

-#ifdef __ASSUME_PRIVATE_FUTEX

-	movl	$FUTEX_WAIT|FUTEX_PRIVATE_FLAG, %esi

-#else

-# if FUTEX_WAIT == 0

-	movl	%fs:PRIVATE_FUTEX, %esi

-# else

-	movl	$FUTEX_WAIT, %esi

-	orl	%fs:PRIVATE_FUTEX, %esi

-# endif

-#endif

-	movl	$SYS_futex, %eax

-	syscall

-	jmp	6b

-

-	/* Preserve the pointer to the control variable.  */

-3:	pushq	%rdi

-	cfi_adjust_cfa_offset(8)

-	pushq	%rdi

-	cfi_adjust_cfa_offset(8)

-

-.LcleanupSTART:

-	callq	*16(%rsp)

-.LcleanupEND:

-

-	/* Get the control variable address back.  */

-	popq	%rdi

-	cfi_adjust_cfa_offset(-8)

-

-	/* Sucessful run of the initializer.  Signal that we are done.  */

-	LOCK

-	incl	(%rdi)

-

-	addq	$8, %rsp

-	cfi_adjust_cfa_offset(-8)

-

-	/* Wake up all other threads.  */

-	movl	$0x7fffffff, %edx

-#ifdef __ASSUME_PRIVATE_FUTEX

-	movl	$FUTEX_WAKE|FUTEX_PRIVATE_FLAG, %esi

-#else

-	movl	$FUTEX_WAKE, %esi

-	orl	%fs:PRIVATE_FUTEX, %esi

-#endif

-	movl	$SYS_futex, %eax

-	syscall

-

-4:	addq	$8, %rsp

-	cfi_adjust_cfa_offset(-8)

-	xorl	%eax, %eax

-	retq

-	.size	__pthread_once,.-__pthread_once

-

-

-hidden_def (__pthread_once)

-strong_alias (__pthread_once, pthread_once)

-

-

-	.type	clear_once_control,@function

-	.align	16

-clear_once_control:

-	cfi_adjust_cfa_offset(3 * 8)

-	movq	(%rsp), %rdi

-	movq	%rax, %r8

-	movl	$0, (%rdi)

-

-	movl	$0x7fffffff, %edx

-#ifdef __ASSUME_PRIVATE_FUTEX

-	movl	$FUTEX_WAKE|FUTEX_PRIVATE_FLAG, %esi

-#else

-	movl	$FUTEX_WAKE, %esi

-	orl	%fs:PRIVATE_FUTEX, %esi

-#endif

-	movl	$SYS_futex, %eax

-	syscall

-

-	movq	%r8, %rdi

-.LcallUR:

-	call	_Unwind_Resume@PLT

-	hlt

-.LENDCODE:

-	cfi_endproc

-	.size	clear_once_control,.-clear_once_control

-

-

-	.section .gcc_except_table,"a",@progbits

-.LexceptSTART:

-	.byte	DW_EH_PE_omit			# @LPStart format

-	.byte	DW_EH_PE_omit			# @TType format

-	.byte	DW_EH_PE_uleb128		# call-site format

-	.uleb128 .Lcstend-.Lcstbegin

-.Lcstbegin:

-	.uleb128 .LcleanupSTART-.LSTARTCODE

-	.uleb128 .LcleanupEND-.LcleanupSTART

-	.uleb128 clear_once_control-.LSTARTCODE

-	.uleb128  0

-	.uleb128 .LcallUR-.LSTARTCODE

-	.uleb128 .LENDCODE-.LcallUR

-	.uleb128 0

-	.uleb128  0

-.Lcstend:

-

-

-#ifdef SHARED

-	.hidden	DW.ref.__gcc_personality_v0

-	.weak	DW.ref.__gcc_personality_v0

-	.section .gnu.linkonce.d.DW.ref.__gcc_personality_v0,"aw",@progbits

-	.align	LP_SIZE

-	.type	DW.ref.__gcc_personality_v0, @object

-	.size	DW.ref.__gcc_personality_v0, LP_SIZE

-DW.ref.__gcc_personality_v0:

-	ASM_ADDR __gcc_personality_v0

-#endif