Manual for platform-specific features and new __ppc_get_timebase inline.

[BZ #13743]
A new class of installed headers has been documented for low-level
platform-specific functionality.  PowerPC added the first instance with a
function to provide time base register access (__ppc_get_timebase).  This
is required for applications that measure time at high frequencies with
high precision that can't afford a syscall.

1 files changed, 47 insertions, 0 deletions

diff --git a/sysdeps/powerpc/sys/platform/ppc.h b/sysdeps/powerpc/sys/platform/ppc.h
new file mode 100644
index 0000000000..165652c7cc
--- /dev/null
+++ b/sysdeps/powerpc/sys/platform/ppc.h
@@ -0,0 +1,47 @@
+/* Facilities specific to the PowerPC architecture
+   Copyright (C) 2012 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 _SYS_PLATFORM_PPC_H
+#define _SYS_PLATFORM_PPC_H	1
+
+#include <stdint.h>
+
+/* Read the Time Base Register.   */
+static inline uint64_t
+__ppc_get_timebase (void)
+{
+#ifdef __powerpc64__
+  uint64_t __tb;
+  /* "volatile" is necessary here, because the user expects this assembly
+     isn't moved after an optimization.  */
+  __asm__ volatile ("mfspr %0, 268" : "=r" (__tb));
+  return __tb;
+#else  /* not __powerpc64__ */
+  uint32_t __tbu, __tbl, __tmp; \
+  __asm__ volatile ("0:\n\t"
+		    "mftbu %0\n\t"
+		    "mftbl %1\n\t"
+		    "mftbu %2\n\t"
+		    "cmpw %0, %2\n\t"
+		    "bne- 0b"
+		    : "=r" (__tbu), "=r" (__tbl), "=r" (__tmp));
+  return (((uint64_t) __tbu << 32) | __tbl);
+#endif  /* not __powerpc64__ */
+}
+
+#endif  /* sys/platform/ppc.h */