nptl: Add struct_rwlock.h

This patch adds a new generic __pthread_rwlock_arch_t definition meant
to be used by new ports.  Its layout mimics the current usage on some
64 bits ports and it allows some ports to use the generic definition.
The arch __pthread_rwlock_arch_t definition is moved from
pthreadtypes-arch.h to another arch-specific header (struct_rwlock.h).

Also the static intialization macro for pthread_rwlock_t is set to use
an arch defined on (__PTHREAD_RWLOCK_INITIALIZER) which simplifies its
implementation.

The default pthread_rwlock_t layout differs from current ports with:

  1. Internal layout is the same for 32 bits and 64 bits.

  2. Internal flag is an unsigned short so it should not required
     additional padding to align for word boundary (if it is the case
     for the ABI).

Checked with a build on affected abis.

Change-Id: I776a6a986c23199929d28a3dcd30272db21cd1d0

2 files changed, 65 insertions, 28 deletions

diff --git a/sysdeps/x86/nptl/bits/pthreadtypes-arch.h b/sysdeps/x86/nptl/bits/pthreadtypes-arch.h
index 668ec4a5d5..426a20751d 100644
--- a/sysdeps/x86/nptl/bits/pthreadtypes-arch.h
+++ b/sysdeps/x86/nptl/bits/pthreadtypes-arch.h
@@ -50,34 +50,6 @@
 #define __LOCK_ALIGNMENT
 #define __ONCE_ALIGNMENT
 
-struct __pthread_rwlock_arch_t
-{
-  unsigned int __readers;
-  unsigned int __writers;
-  unsigned int __wrphase_futex;
-  unsigned int __writers_futex;
-  unsigned int __pad3;
-  unsigned int __pad4;
-#ifdef __x86_64__
-  int __cur_writer;
-  int __shared;
-  unsigned long int __pad1;
-  unsigned long int __pad2;
-  /* FLAGS must stay at this position in the structure to maintain
-     binary compatibility.  */
-  unsigned int __flags;
-# define __PTHREAD_RWLOCK_INT_FLAGS_SHARED	1
-#else
-  /* FLAGS must stay at this position in the structure to maintain
-     binary compatibility.  */
-  unsigned char __flags;
-  unsigned char __shared;
-  unsigned char __pad1;
-  unsigned char __pad2;
-  int __cur_writer;
-#endif
-};
-
 #ifndef __x86_64__
 /* Extra attributes for the cleanup functions.  */
 # define __cleanup_fct_attribute __attribute__ ((__regparm__ (1)))
diff --git a/sysdeps/x86/nptl/bits/struct_rwlock.h b/sysdeps/x86/nptl/bits/struct_rwlock.h
new file mode 100644
index 0000000000..7f4728ec84
--- /dev/null
+++ b/sysdeps/x86/nptl/bits/struct_rwlock.h
@@ -0,0 +1,65 @@
+/* x86 internal rwlock struct definitions.
+   Copyright (C) 2019 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 _RWLOCK_INTERNAL_H
+#define _RWLOCK_INTERNAL_H
+
+struct __pthread_rwlock_arch_t
+{
+  unsigned int __readers;
+  unsigned int __writers;
+  unsigned int __wrphase_futex;
+  unsigned int __writers_futex;
+  unsigned int __pad3;
+  unsigned int __pad4;
+#ifdef __x86_64__
+  int __cur_writer;
+  int __shared;
+  signed char __rwelision;
+# ifdef  __ILP32__
+  unsigned char __pad1[3];
+#  define __PTHREAD_RWLOCK_ELISION_EXTRA 0, { 0, 0, 0 }
+# else
+  unsigned char __pad1[7];
+#  define __PTHREAD_RWLOCK_ELISION_EXTRA 0, { 0, 0, 0, 0, 0, 0, 0 }
+# endif
+  unsigned long int __pad2;
+  /* FLAGS must stay at this position in the structure to maintain
+     binary compatibility.  */
+  unsigned int __flags;
+#else /* __x86_64__  */
+  /* FLAGS must stay at this position in the structure to maintain
+     binary compatibility.  */
+  unsigned char __flags;
+  unsigned char __shared;
+  signed char __rwelision;
+  unsigned char __pad2;
+  int __cur_writer;
+#endif
+};
+
+#ifdef __x86_64__
+# define __PTHREAD_RWLOCK_INITIALIZER(__flags) \
+  0, 0, 0, 0, 0, 0, 0, 0, __PTHREAD_RWLOCK_ELISION_EXTRA, 0, __flags
+#else
+# define __PTHREAD_RWLOCK_INITIALIZER(__flags) \
+  0, 0, 0, 0, 0, 0, __flags, 0, 0, 0, 0
+#endif
+
+#endif