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[COMMITTED PATCH] Separate Linuxisms from lowlevellock.h, make a generic one


I've committed the new files that were previously posted on the
roland/lll-futex branch.  This does not affect any existing configuration
yet.  Each machine can simply remove its lowlevellock.h file to start using
the generic code and see how it compares.

This "generic" code is based on the existing ARM and AArch64 code.  It's
known to have the BZ#16892 bug but we'd like to fix that only after some
machine(s) have switched to actually using this code so that there can be
separate tree states for converting the machine to use the generic code,
which is intended to have zero semantic effect and expected to have minimal
effect on the compiled code; and then fixing BZ#16892, which changes the
semantics slightly.

I've build-tested this on arm-linux-gnueabihf and aarch64-linux-gnu, by
removing sysdeps/unix/sysv/linux/CPU/lowlevellock.h.  On both those
machines, there were a lot more changes to generated code than I was
expecting, but in everything I examined the differences seemed to be in
arbitrary code-generation choices by the compiler and not directly related
to the lowlevellock.h differences.  I don't understand why those
differences appeared.  Someone who groks the compiler well could look at
them and try to make sense of it for our edification.

I've also run the test suite on arm-linux-gnueabihf to compare the status
quo ante with this code (and arm/lowlevellock.h removed, which is not
committed yet).  There were no regressions.


Thanks,
Roland


	* sysdeps/nptl/lowlevellock.h: New file.
	* sysdeps/unix/sysv/linux/lowlevellock-futex.h: New file.
	* sysdeps/nptl/lowlevellock-futex.h: New file.

--- /dev/null
+++ b/sysdeps/nptl/lowlevellock-futex.h
@@ -0,0 +1,86 @@
+/* Low-level locking access to futex facilities.  Stub version.
+   Copyright (C) 2014 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/>.  */
+
+#ifndef _LOWLEVELLOCK_FUTEX_H
+#define _LOWLEVELLOCK_FUTEX_H   1
+
+#include <errno.h>
+
+
+/* Values for 'private' parameter of locking macros.  Note pthreadP.h
+   optimizes for these exact values, though they are not required.  */
+#define LLL_PRIVATE     0
+#define LLL_SHARED      128
+
+
+/* For most of these macros, the return value is never really used.
+   Nevertheless, the protocol is that each one returns a negated errno
+   code for failure or zero for success.  (Note that the corresponding
+   Linux system calls can sometimes return positive values for success
+   cases too.  We never use those values.)  */
+
+
+/* Wait while *FUTEXP == VAL for an lll_futex_wake call on FUTEXP.  */
+#define lll_futex_wait(futexp, val, private) \
+  lll_futex_timed_wait (futexp, val, NULL, private)
+
+/* Wait until a lll_futex_wake call on FUTEXP, or TIMEOUT elapses.  */
+#define lll_futex_timed_wait(futexp, val, timeout, private)             \
+  -ENOSYS
+
+/* This macro should be defined only if FUTEX_CLOCK_REALTIME is also defined.
+   If CLOCKBIT is zero, this is identical to lll_futex_timed_wait.
+   If CLOCKBIT has FUTEX_CLOCK_REALTIME set, then it's the same but
+   TIMEOUT is counted by CLOCK_REALTIME rather than CLOCK_MONOTONIC.  */
+#define lll_futex_timed_wait_bitset(futexp, val, timeout, clockbit, private) \
+  -ENOSYS
+
+/* Wake up up to NR waiters on FUTEXP.  */
+#define lll_futex_wake(futexp, nr, private)                             \
+  -ENOSYS
+
+/* Wake up up to NR_WAKE waiters on FUTEXP.  Move up to NR_MOVE of the
+   rest from waiting on FUTEXP to waiting on MUTEX (a different futex).  */
+#define lll_futex_requeue(futexp, nr_wake, nr_move, mutex, val, private) \
+  -ENOSYS
+
+/* Wake up up to NR_WAKE waiters on FUTEXP and NR_WAKE2 on FUTEXP2.  */
+#define lll_futex_wake_unlock(futexp, nr_wake, nr_wake2, futexp2, private) \
+  -ENOSYS
+
+
+/* Like lll_futex_wait (FUTEXP, VAL, PRIVATE) but with the expectation
+   that lll_futex_cmp_requeue_pi (FUTEXP, _, _, MUTEX, _, PRIVATE) will
+   be used to do the wakeup.  Confers priority-inheritance behavior on
+   the waiter.  */
+#define lll_futex_wait_requeue_pi(futexp, val, mutex, private) \
+  lll_futex_timed_wait_requeue_pi (futexp, val, NULL, 0, mutex, private)
+
+/* Like lll_futex_wait_requeue_pi, but with a timeout.  */
+#define lll_futex_timed_wait_requeue_pi(futexp, val, timeout, clockbit, \
+                                        mutex, private)                 \
+  -ENOSYS
+
+/* Like lll_futex_requeue, but pairs with lll_futex_wait_requeue_pi
+   and inherits priority from the waiter.  */
+#define lll_futex_cmp_requeue_pi(futexp, nr_wake, nr_move, mutex,       \
+                                 val, private)                          \
+  -ENOSYS
+
+
+#endif  /* lowlevellock-futex.h */
--- /dev/null
+++ b/sysdeps/nptl/lowlevellock.h
@@ -0,0 +1,187 @@
+/* Low-level lock implementation.  Generic futex-based version.
+   Copyright (C) 2005-2014 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/>.  */
+
+#ifndef _LOWLEVELLOCK_H
+#define _LOWLEVELLOCK_H	1
+
+#include <atomic.h>
+#include <lowlevellock-futex.h>
+
+#define lll_trylock(lock)	\
+  atomic_compare_and_exchange_bool_acq (&(lock), 1, 0)
+
+#define lll_cond_trylock(lock)	\
+  atomic_compare_and_exchange_bool_acq (&(lock), 2, 0)
+
+extern void __lll_lock_wait_private (int *futex) attribute_hidden;
+extern void __lll_lock_wait (int *futex, int private) attribute_hidden;
+extern int __lll_robust_lock_wait (int *futex, int private) attribute_hidden;
+
+/* This is an expression rather than a statement even though its value is
+   void, so that it can be used in a comma expression or as an expression
+   that's cast to void.  */
+#define __lll_lock(futex, private)                                      \
+  ((void)                                                               \
+   ({                                                                   \
+     int *__futex = (futex);                                            \
+     if (__glibc_unlikely                                               \
+         (atomic_compare_and_exchange_bool_acq (__futex, 1, 0)))        \
+       {                                                                \
+         if (__builtin_constant_p (private) && (private) == LLL_PRIVATE) \
+           __lll_lock_wait_private (__futex);                           \
+         else                                                           \
+           __lll_lock_wait (__futex, private);                          \
+       }                                                                \
+   }))
+#define lll_lock(futex, private)	\
+  __lll_lock (&(futex), private)
+
+
+#define __lll_robust_lock(futex, id, private)                           \
+  ({                                                                    \
+    int *__futex = (futex);                                             \
+    int __val = 0;                                                      \
+                                                                        \
+    if (__glibc_unlikely                                                \
+        (atomic_compare_and_exchange_bool_acq (__futex, id, 0)))        \
+      __val = __lll_robust_lock_wait (__futex, private);                \
+    __val;                                                              \
+  })
+#define lll_robust_lock(futex, id, private)     \
+  __lll_robust_lock (&(futex), id, private)
+
+
+/* This is an expression rather than a statement even though its value is
+   void, so that it can be used in a comma expression or as an expression
+   that's cast to void.  */
+#define __lll_cond_lock(futex, private)                                 \
+  ((void)                                                               \
+   ({                                                                   \
+     int *__futex = (futex);                                            \
+     if (__glibc_unlikely (atomic_exchange_acq (__futex, 2) != 0))      \
+       __lll_lock_wait (__futex, private);                              \
+   }))
+#define lll_cond_lock(futex, private) __lll_cond_lock (&(futex), private)
+
+
+#define lll_robust_cond_lock(futex, id, private)	\
+  __lll_robust_lock (&(futex), (id) | FUTEX_WAITERS, private)
+
+
+extern int __lll_timedlock_wait (int *futex, const struct timespec *,
+				 int private) attribute_hidden;
+extern int __lll_robust_timedlock_wait (int *futex, const struct timespec *,
+					int private) attribute_hidden;
+
+#define __lll_timedlock(futex, abstime, private)                \
+  ({                                                            \
+    int *__futex = (futex);                                     \
+    int __val = 0;                                              \
+                                                                \
+    if (__glibc_unlikely (atomic_exchange_acq (__futex, 1)))    \
+      __val = __lll_timedlock_wait (__futex, abstime, private); \
+    __val;                                                      \
+  })
+#define lll_timedlock(futex, abstime, private)  \
+  __lll_timedlock (&(futex), abstime, private)
+
+
+#define __lll_robust_timedlock(futex, abstime, id, private)             \
+  ({                                                                    \
+    int *__futex = (futex);                                             \
+    int __val = 0;                                                      \
+                                                                        \
+    if (__glibc_unlikely                                                \
+        (atomic_compare_and_exchange_bool_acq (__futex, id, 0)))        \
+      __val = __lll_robust_timedlock_wait (__futex, abstime, private);  \
+    __val;                                                              \
+  })
+#define lll_robust_timedlock(futex, abstime, id, private)       \
+  __lll_robust_timedlock (&(futex), abstime, id, private)
+
+
+/* This is an expression rather than a statement even though its value is
+   void, so that it can be used in a comma expression or as an expression
+   that's cast to void.  */
+#define __lll_unlock(futex, private)                    \
+  ((void)                                               \
+   ({                                                   \
+     int *__futex = (futex);                            \
+     int __oldval = atomic_exchange_rel (__futex, 0);   \
+     if (__glibc_unlikely (__oldval > 1))               \
+       lll_futex_wake (__futex, 1, private);            \
+   }))
+#define lll_unlock(futex, private)	\
+  __lll_unlock (&(futex), private)
+
+
+/* This is an expression rather than a statement even though its value is
+   void, so that it can be used in a comma expression or as an expression
+   that's cast to void.  */
+#define __lll_robust_unlock(futex, private)             \
+  ((void)                                               \
+   ({                                                   \
+     int *__futex = (futex);                            \
+     int __oldval = atomic_exchange_rel (__futex, 0);   \
+     if (__glibc_unlikely (__oldval & FUTEX_WAITERS))	\
+       lll_futex_wake (__futex, 1, private);            \
+   }))
+#define lll_robust_unlock(futex, private)       \
+  __lll_robust_unlock (&(futex), private)
+
+
+#define lll_islocked(futex) \
+  ((futex) != LLL_LOCK_INITIALIZER)
+
+
+/* Our internal lock implementation is identical to the binary-compatible
+   mutex implementation. */
+
+/* Initializers for lock.  */
+#define LLL_LOCK_INITIALIZER		(0)
+#define LLL_LOCK_INITIALIZER_LOCKED	(1)
+
+/* The states of a lock are:
+    0  -  untaken
+    1  -  taken by one user
+   >1  -  taken by more users */
+
+/* The kernel notifies a process which uses CLONE_CHILD_CLEARTID via futex
+   wakeup when the clone terminates.  The memory location contains the
+   thread ID while the clone is running and is reset to zero
+   afterwards.	*/
+#define lll_wait_tid(tid) \
+  do {					\
+    __typeof (tid) __tid;		\
+    while ((__tid = (tid)) != 0)	\
+      lll_futex_wait (&(tid), __tid, LLL_SHARED);\
+  } while (0)
+
+extern int __lll_timedwait_tid (int *, const struct timespec *)
+     attribute_hidden;
+
+#define lll_timedwait_tid(tid, abstime) \
+  ({							\
+    int __res = 0;					\
+    if ((tid) != 0)					\
+      __res = __lll_timedwait_tid (&(tid), (abstime));	\
+    __res;						\
+  })
+
+
+#endif	/* lowlevellock.h */
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/lowlevellock-futex.h
@@ -0,0 +1,137 @@
+/* Low-level locking access to futex facilities.  Linux version.
+   Copyright (C) 2005-2014 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/>.  */
+
+#ifndef _LOWLEVELLOCK_FUTEX_H
+#define _LOWLEVELLOCK_FUTEX_H	1
+
+#include <sysdep.h>
+#include <tls.h>
+#include <kernel-features.h>
+
+
+#define FUTEX_WAIT		0
+#define FUTEX_WAKE		1
+#define FUTEX_REQUEUE		3
+#define FUTEX_CMP_REQUEUE	4
+#define FUTEX_WAKE_OP		5
+#define FUTEX_OP_CLEAR_WAKE_IF_GT_ONE	((4 << 24) | 1)
+#define FUTEX_LOCK_PI		6
+#define FUTEX_UNLOCK_PI		7
+#define FUTEX_TRYLOCK_PI	8
+#define FUTEX_WAIT_BITSET	9
+#define FUTEX_WAKE_BITSET	10
+#define FUTEX_WAIT_REQUEUE_PI   11
+#define FUTEX_CMP_REQUEUE_PI    12
+#define FUTEX_PRIVATE_FLAG	128
+#define FUTEX_CLOCK_REALTIME	256
+
+#define FUTEX_BITSET_MATCH_ANY	0xffffffff
+
+/* Values for 'private' parameter of locking macros.  Yes, the
+   definition seems to be backwards.  But it is not.  The bit will be
+   reversed before passing to the system call.  */
+#define LLL_PRIVATE	0
+#define LLL_SHARED	FUTEX_PRIVATE_FLAG
+
+
+#if !defined NOT_IN_libc || defined IS_IN_rtld
+/* In libc.so or ld.so all futexes are private.  */
+# ifdef __ASSUME_PRIVATE_FUTEX
+#  define __lll_private_flag(fl, private) \
+  ((fl) | FUTEX_PRIVATE_FLAG)
+# else
+#  define __lll_private_flag(fl, private) \
+  ((fl) | THREAD_GETMEM (THREAD_SELF, header.private_futex))
+# endif
+#else
+# ifdef __ASSUME_PRIVATE_FUTEX
+#  define __lll_private_flag(fl, private) \
+  (((fl) | FUTEX_PRIVATE_FLAG) ^ (private))
+# else
+#  define __lll_private_flag(fl, private) \
+  (__builtin_constant_p (private)					      \
+   ? ((private) == 0							      \
+      ? ((fl) | THREAD_GETMEM (THREAD_SELF, header.private_futex))	      \
+      : (fl))								      \
+   : ((fl) | (((private) ^ FUTEX_PRIVATE_FLAG)				      \
+	      & THREAD_GETMEM (THREAD_SELF, header.private_futex))))
+# endif
+#endif
+
+#define lll_futex_syscall(nargs, futexp, op, ...)                       \
+  ({                                                                    \
+    INTERNAL_SYSCALL_DECL (__err);                                      \
+    long int __ret = INTERNAL_SYSCALL (futex, __err, nargs, futexp, op, \
+				       __VA_ARGS__);                    \
+    (__glibc_unlikely (INTERNAL_SYSCALL_ERROR_P (__ret, __err))         \
+     ? -INTERNAL_SYSCALL_ERRNO (__ret, __err) : 0);                     \
+  })
+
+#define lll_futex_wait(futexp, val, private) \
+  lll_futex_timed_wait (futexp, val, NULL, private)
+
+#define lll_futex_timed_wait(futexp, val, timeout, private)     \
+  lll_futex_syscall (4, futexp,                                 \
+		     __lll_private_flag (FUTEX_WAIT, private),  \
+		     val, timeout)
+
+#define lll_futex_timed_wait_bitset(futexp, val, timeout, clockbit, private) \
+  lll_futex_syscall (6, futexp,                                         \
+		     __lll_private_flag (FUTEX_WAIT_BITSET | (clockbit), \
+					 private),                      \
+		     val, timeout, NULL /* Unused.  */,                 \
+		     FUTEX_BITSET_MATCH_ANY)
+
+#define lll_futex_wake(futexp, nr, private)                             \
+  lll_futex_syscall (4, futexp,                                         \
+		     __lll_private_flag (FUTEX_WAKE, private), nr, 0)
+
+/* Returns non-zero if error happened, zero if success.  */
+#define lll_futex_requeue(futexp, nr_wake, nr_move, mutex, val, private) \
+  lll_futex_syscall (6, futexp,                                         \
+		     __lll_private_flag (FUTEX_CMP_REQUEUE, private),   \
+		     nr_wake, nr_move, mutex, val)
+
+/* Returns non-zero if error happened, zero if success.  */
+#define lll_futex_wake_unlock(futexp, nr_wake, nr_wake2, futexp2, private) \
+  lll_futex_syscall (6, futexp,                                         \
+		     __lll_private_flag (FUTEX_WAKE_OP, private),       \
+		     nr_wake, nr_wake2, futexp2,                        \
+		     FUTEX_OP_CLEAR_WAKE_IF_GT_ONE)
+
+/* Priority Inheritance support.  */
+#define lll_futex_wait_requeue_pi(futexp, val, mutex, private) \
+  lll_futex_timed_wait_requeue_pi (futexp, val, NULL, 0, mutex, private)
+
+#define lll_futex_timed_wait_requeue_pi(futexp, val, timeout, clockbit, \
+					mutex, private)                 \
+  lll_futex_syscall (5, futexp,                                         \
+		     __lll_private_flag (FUTEX_WAIT_REQUEUE_PI          \
+					 | (clockbit), private),        \
+		     val, timeout, mutex)
+
+
+#define lll_futex_cmp_requeue_pi(futexp, nr_wake, nr_move, mutex,       \
+				 val, private)                          \
+  lll_futex_syscall (6, futexp,                                         \
+		     __lll_private_flag (FUTEX_CMP_REQUEUE_PI,          \
+					 private),                      \
+		     nr_wake, nr_move, mutex, val)
+
+
+#endif  /* lowlevellock-futex.h */


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