commit f0458cf4f9ff3d870c43b624e6dccaaf657d5e83

Author: Adhemerval Zanella <adhemerval.zanella@linaro.org>

Date:   Mon Aug 27 09:42:50 2018 -0300

    powerpc: Only enable TLE with PPC_FEATURE2_HTM_NOSC

    Linux from 3.9 through 4.2 does not abort HTM transaction on syscalls,

    instead it suspend and resume it when leaving the kernel.  The

    side-effects of the syscall will always remain visible, even if the

    transaction is aborted.  This is an issue when transaction is used along

    with futex syscall, on pthread_cond_wait for instance, where the futex

    call might succeed but the transaction is rolled back leading the

    pthread_cond object in an inconsistent state.

    Glibc used to prevent it by always aborting a transaction before issuing

    a syscall.  Linux 4.2 also decided to abort active transaction in

    syscalls which makes the glibc workaround superfluous.  Worse, glibc

    transaction abortion leads to a performance issue on recent kernels

    where the HTM state is saved/restore lazily (v4.9).  By aborting a

    transaction on every syscalls, regardless whether a transaction has being

    initiated before, GLIBS makes the kernel always save/restore HTM state

    (it can not even lazily disable it after a certain number of syscall

    iterations).

    Because of this shortcoming, Transactional Lock Elision is just enabled

    when it has been explicitly set (either by tunables of by a configure

    switch) and if kernel aborts HTM transactions on syscalls

    (PPC_FEATURE2_HTM_NOSC).  It is reported that using simple benchmark [1],

    the context-switch is about 5% faster by not issuing a tabort in every

    syscall in newer kernels.

    Checked on powerpc64le-linux-gnu with 4.4.0 kernel (Ubuntu 16.04).

    	* NEWS: Add note about new TLE support on powerpc64le.

    	* sysdeps/powerpc/nptl/tcb-offsets.sym (TM_CAPABLE): Remove.

    	* sysdeps/powerpc/nptl/tls.h (tcbhead_t): Rename tm_capable to

    	__ununsed1.

    	(TLS_INIT_TP, TLS_DEFINE_INIT_TP): Remove tm_capable setup.

    	(THREAD_GET_TM_CAPABLE, THREAD_SET_TM_CAPABLE): Remove macros.

    	* sysdeps/powerpc/powerpc32/sysdep.h,

    	sysdeps/powerpc/powerpc64/sysdep.h (ABORT_TRANSACTION_IMPL,

    	ABORT_TRANSACTION): Remove macros.

    	* sysdeps/powerpc/sysdep.h (ABORT_TRANSACTION): Likewise.

    	* sysdeps/unix/sysv/linux/powerpc/elision-conf.c (elision_init): Set

    	__pthread_force_elision iff PPC_FEATURE2_HTM_NOSC is set.

    	* sysdeps/unix/sysv/linux/powerpc/powerpc32/sysdep.h,

    	sysdeps/unix/sysv/linux/powerpc/powerpc64/sysdep.h

    	sysdeps/unix/sysv/linux/powerpc/syscall.S (ABORT_TRANSACTION): Remove

    	usage.

    	* sysdeps/unix/sysv/linux/powerpc/not-errno.h: Remove file.

    Reported-by: Breno Leitão <leitao@debian.org>

diff --git a/sysdeps/powerpc/nptl/tcb-offsets.sym b/sysdeps/powerpc/nptl/tcb-offsets.sym

index e5bb2b3..4c01615 100644

--- a/sysdeps/powerpc/nptl/tcb-offsets.sym

+++ b/sysdeps/powerpc/nptl/tcb-offsets.sym

@@ -21,7 +21,6 @@ DSO_SLOT2			(offsetof (tcbhead_t, dso_slot2) - TLS_TCB_OFFSET - sizeof (tcbhead_

 #ifdef __powerpc64__

 TCB_AT_PLATFORM			(offsetof (tcbhead_t, at_platform) - TLS_TCB_OFFSET - sizeof(tcbhead_t))

 #endif

-TM_CAPABLE			(offsetof (tcbhead_t, tm_capable) - TLS_TCB_OFFSET - sizeof (tcbhead_t))

 #ifndef __powerpc64__

 TCB_AT_PLATFORM			(offsetof (tcbhead_t, at_platform) - TLS_TCB_OFFSET - sizeof(tcbhead_t))

 PADDING				(offsetof (tcbhead_t, padding) - TLS_TCB_OFFSET - sizeof(tcbhead_t))

diff --git a/sysdeps/powerpc/nptl/tls.h b/sysdeps/powerpc/nptl/tls.h

index f88fed5..8317ca7 100644

--- a/sysdeps/powerpc/nptl/tls.h

+++ b/sysdeps/powerpc/nptl/tls.h

@@ -67,8 +67,7 @@ typedef struct

   uint32_t padding;

   uint32_t at_platform;

 #endif

-  /* Indicate if HTM capable (ISA 2.07).  */

-  uint32_t tm_capable;

+  uint32_t __unused;

   /* Reservation for AT_PLATFORM data - powerpc64.  */

 #ifdef __powerpc64__

   uint32_t at_platform;

@@ -142,7 +141,6 @@ register void *__thread_register __asm__ ("r13");

 # define TLS_INIT_TP(tcbp) \

   ({ 									      \

     __thread_register = (void *) (tcbp) + TLS_TCB_OFFSET;		      \

-    THREAD_SET_TM_CAPABLE (__tcb_hwcap & PPC_FEATURE2_HAS_HTM ? 1 : 0);	      \

     THREAD_SET_HWCAP (__tcb_hwcap);					      \

     THREAD_SET_AT_PLATFORM (__tcb_platform);				      \

     NULL;								      \

@@ -151,8 +149,6 @@ register void *__thread_register __asm__ ("r13");

 /* Value passed to 'clone' for initialization of the thread register.  */

 # define TLS_DEFINE_INIT_TP(tp, pd) \

     void *tp = (void *) (pd) + TLS_TCB_OFFSET + TLS_PRE_TCB_SIZE;	      \

-    (((tcbhead_t *) ((char *) tp - TLS_TCB_OFFSET))[-1].tm_capable) =	      \

-      THREAD_GET_TM_CAPABLE ();						      \

     (((tcbhead_t *) ((char *) tp - TLS_TCB_OFFSET))[-1].hwcap) =	      \

       THREAD_GET_HWCAP ();						      \

     (((tcbhead_t *) ((char *) tp - TLS_TCB_OFFSET))[-1].at_platform) =	      \

@@ -210,13 +206,6 @@ register void *__thread_register __asm__ ("r13");

 		     + TLS_PRE_TCB_SIZE))[-1].pointer_guard		      \

      = THREAD_GET_POINTER_GUARD())

-/* tm_capable field in TCB head.  */

-# define THREAD_GET_TM_CAPABLE() \

-    (((tcbhead_t *) ((char *) __thread_register				      \

-		     - TLS_TCB_OFFSET))[-1].tm_capable)

-# define THREAD_SET_TM_CAPABLE(value) \

-    (THREAD_GET_TM_CAPABLE () = (value))

-

 /* hwcap field in TCB head.  */

 # define THREAD_GET_HWCAP() \

     (((tcbhead_t *) ((char *) __thread_register				      \

diff --git a/sysdeps/powerpc/powerpc32/sysdep.h b/sysdeps/powerpc/powerpc32/sysdep.h

index 5f1294e..93097c5 100644

--- a/sysdeps/powerpc/powerpc32/sysdep.h

+++ b/sysdeps/powerpc/powerpc32/sysdep.h

@@ -90,24 +90,7 @@ GOT_LABEL:			;					      \

   cfi_endproc;								      \

   ASM_SIZE_DIRECTIVE(name)

-#if !IS_IN(rtld) && !defined(__SPE__)

-# define ABORT_TRANSACTION_IMPL \

-    cmpwi    2,0;		\

-    beq      1f;		\

-    lwz      0,TM_CAPABLE(2);	\

-    cmpwi    0,0;		\

-    beq	     1f;		\

-    li       11,_ABORT_SYSCALL;	\

-    tabort.  11;		\

-    .align 4;			\

-1:

-#else

-# define ABORT_TRANSACTION_IMPL

-#endif

-#define ABORT_TRANSACTION ABORT_TRANSACTION_IMPL

-

 #define DO_CALL(syscall)						      \

-    ABORT_TRANSACTION							      \

     li 0,syscall;							      \

     sc

diff --git a/sysdeps/powerpc/powerpc64/sysdep.h b/sysdeps/powerpc/powerpc64/sysdep.h

index 2df1d9b..50e64f9 100644

--- a/sysdeps/powerpc/powerpc64/sysdep.h

+++ b/sysdeps/powerpc/powerpc64/sysdep.h

@@ -263,24 +263,7 @@ LT_LABELSUFFIX(name,_name_end): ; \

   TRACEBACK_MASK(name,mask);	\

   END_2(name)

-#if !IS_IN(rtld)

-# define ABORT_TRANSACTION_IMPL \

-    cmpdi    13,0;		\

-    beq      1f;		\

-    lwz      0,TM_CAPABLE(13);	\

-    cmpwi    0,0;		\

-    beq	     1f;		\

-    li       11,_ABORT_SYSCALL;	\

-    tabort.  11;		\

-    .p2align 4;			\

-1:

-#else

-# define ABORT_TRANSACTION_IMPL

-#endif

-#define ABORT_TRANSACTION ABORT_TRANSACTION_IMPL

-

 #define DO_CALL(syscall) \

-    ABORT_TRANSACTION \

     li 0,syscall; \

     sc

diff --git a/sysdeps/powerpc/sysdep.h b/sysdeps/powerpc/sysdep.h

index 8a6d236..c8bf25e 100644

--- a/sysdeps/powerpc/sysdep.h

+++ b/sysdeps/powerpc/sysdep.h

@@ -21,8 +21,6 @@

  */

 #define _SYSDEPS_SYSDEP_H 1

 #include <bits/hwcap.h>

-#include <tls.h>

-#include <htm.h>

 #define PPC_FEATURE_970 (PPC_FEATURE_POWER4 + PPC_FEATURE_HAS_ALTIVEC)

@@ -166,22 +164,4 @@

 #define ALIGNARG(log2) log2

 #define ASM_SIZE_DIRECTIVE(name) .size name,.-name

-#else

-

-/* Linux kernel powerpc documentation [1] states issuing a syscall inside a

-   transaction is not recommended and may lead to undefined behavior.  It

-   also states syscalls do not abort transactions.  To avoid such traps,

-   we abort transaction just before syscalls.

-

-   [1] Documentation/powerpc/transactional_memory.txt [Syscalls]  */

-#if !IS_IN(rtld) && !defined(__SPE__)

-# define ABORT_TRANSACTION \

-  ({ 						\

-    if (THREAD_GET_TM_CAPABLE ())		\

-      __libc_tabort (_ABORT_SYSCALL);	\

-  })

-#else

-# define ABORT_TRANSACTION

-#endif

-

 #endif	/* __ASSEMBLER__ */

diff --git a/sysdeps/unix/sysv/linux/powerpc/elision-conf.c b/sysdeps/unix/sysv/linux/powerpc/elision-conf.c

index 906882a..fc82bd1 100644

--- a/sysdeps/unix/sysv/linux/powerpc/elision-conf.c

+++ b/sysdeps/unix/sysv/linux/powerpc/elision-conf.c

@@ -127,6 +127,26 @@ elision_init (int argc __attribute__ ((unused)),

 	       TUNABLE_CALLBACK (set_elision_skip_trylock_internal_abort));

 #endif

+  /* Linux from 3.9 through 4.2 do not abort HTM transaction on syscalls,

+     instead it suspends the transaction and resumes it when returning to

+     usercode.  The side-effects of the syscall will always remain visible,

+     even if the transaction is aborted.  This is an issue when a transaction

+     is used along with futex syscall, on pthread_cond_wait for instance,

+     where futex might succeed but the transaction is rolled back leading

+     the condition variable object in an inconsistent state.

+

+     Glibc used to prevent it by always aborting a transaction before issuing

+     a syscall.  Linux 4.2 also decided to abort active transaction in

+     syscalls which makes the glibc workaround superflours.  Worse, glibc

+     transaction abortions leads to a performance issues on recent kernels.

+

+     So Lock Elision is just enabled when it has been explict set (either

+     by tunables of by a configure switch) and if kernel aborts HTM

+     transactions on syscalls (PPC_FEATURE2_HTM_NOSC)  */

+

+  __pthread_force_elision = (__pthread_force_elision

+			     && GLRO (dl_hwcap2) & PPC_FEATURE2_HTM_NOSC);

+

   if (!__pthread_force_elision)

     __elision_aconf.try_tbegin = 0; /* Disable elision on rwlocks.  */

 }

diff --git a/sysdeps/unix/sysv/linux/powerpc/not-errno.h b/sysdeps/unix/sysv/linux/powerpc/not-errno.h

deleted file mode 100644

index 27da21b..0000000

--- a/sysdeps/unix/sysv/linux/powerpc/not-errno.h

+++ /dev/null

@@ -1,30 +0,0 @@

-/* Syscall wrapper that do not set errno.  Linux powerpc version.

-   Copyright (C) 2018 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

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

-

-/* __access_noerrno is used during process initialization in elf/dl-tunables.c

-   before the TCB is initialized, prohibiting the usage of

-   ABORT_TRANSACTION.  */

-#undef ABORT_TRANSACTION

-#define ABORT_TRANSACTION

-

-#include "sysdeps/unix/sysv/linux/not-errno.h"

-

-/* Recover ABORT_TRANSACTION's previous value, in order to not affect

-   other syscalls.  */

-#undef ABORT_TRANSACTION

-#define ABORT_TRANSACTION ABORT_TRANSACTION_IMPL

diff --git a/sysdeps/unix/sysv/linux/powerpc/powerpc32/sysdep.h b/sysdeps/unix/sysv/linux/powerpc/powerpc32/sysdep.h

index f7277d5..ec5c525 100644

--- a/sysdeps/unix/sysv/linux/powerpc/powerpc32/sysdep.h

+++ b/sysdeps/unix/sysv/linux/powerpc/powerpc32/sysdep.h

@@ -109,7 +109,6 @@

     register long int r11 __asm__ ("r11");				\

     register long int r12 __asm__ ("r12");				\

     LOADARGS_##nr(name, args);						\

-    ABORT_TRANSACTION;							\

     __asm__ __volatile__						\

       ("sc   \n\t"							\

        "mfcr %0"							\

diff --git a/sysdeps/unix/sysv/linux/powerpc/powerpc64/sysdep.h b/sysdeps/unix/sysv/linux/powerpc/powerpc64/sysdep.h

index 0956cf0..1f17f7b 100644

--- a/sysdeps/unix/sysv/linux/powerpc/powerpc64/sysdep.h

+++ b/sysdeps/unix/sysv/linux/powerpc/powerpc64/sysdep.h

@@ -131,7 +131,6 @@

     register long int r7  __asm__ ("r7");				\

     register long int r8  __asm__ ("r8");				\

     LOADARGS_##nr (name, ##args);					\

-    ABORT_TRANSACTION;							\

     __asm__ __volatile__						\

       ("sc\n\t"								\

        "mfcr  %0\n\t"							\

diff --git a/sysdeps/unix/sysv/linux/powerpc/syscall.S b/sysdeps/unix/sysv/linux/powerpc/syscall.S

index 2da9172..bbab613 100644

--- a/sysdeps/unix/sysv/linux/powerpc/syscall.S

+++ b/sysdeps/unix/sysv/linux/powerpc/syscall.S

@@ -18,7 +18,6 @@

 #include <sysdep.h>

 ENTRY (syscall)

-	ABORT_TRANSACTION

 	mr   r0,r3

 	mr   r3,r4

 	mr   r4,r5