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Manual for platform-specific features and new __ppc_get_timebase inline.

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[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.
This commit is contained in:
Tulio Magno Quites Machado Filho 2012-06-04 13:46:37 -05:00 committed by Ryan S. Arnold
parent 06775cb82b
commit d9dc34cd56
9 changed files with 238 additions and 12 deletions
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14
ChangeLog
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@ -1,3 +1,17 @@
2012-06-04 Tulio Magno Quites Machado Filho <tuliom@linux.vnet.ibm.com>
[BZ #13743]
* sysdeps/powerpc/sys/platform/ppc.h: New file for PowerPC features.
* sysdeps/powerpc/Makefile (tests): Add test-gettimebase.
(sysdep_headers): Include sys/platform/ppc.h.
* sysdeps/powerpc/test-gettimebase.c: Test for
__ppc_get_timebase() to catch future ISA opcode/insn changes.
* manual/Makefile (appendices): Include platform.texi.
* manual/contrib.texi (Contributors): Update @node pointers.
* manual/maint.texi (Maintenance): Likewise.
(Platform): New node.
* manual/platform.texi: New file. Document the new features.
2012-06-04 Siddhesh Poyarekar <siddhesh@redhat.com>
Jakub Jelinek <jakub@redhat.com>

24
NEWS
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@ -13,14 +13,14 @@ Version 2.16
2551, 2552, 2553, 2554, 2562, 2563, 2565, 2566, 2570, 2576, 2636, 2678,
3335, 3440, 3748, 3768, 3866, 3868, 3906, 3976, 3992, 4026, 4108, 4596,
4822, 5077, 5461, 5805, 5993, 6471, 6486, 6578, 6649, 6730, 6770, 6794,
6884, 6890, 6894, 6895, 6907, 6911, 6959, 7064, 9739, 9902, 10110,
10135, 10140, 10153, 10210, 10254, 10346, 10375, 10545, 10716, 10846,
11174, 11322, 11365, 11451, 11494, 11521, 11677, 11837, 11959, 12047,
12097, 12193, 12297, 12298, 12301, 12340, 12354, 12416, 12495, 13058,
13223, 13361, 13525, 13526, 13527, 13528, 13529, 13530, 13531, 13532,
13533, 13547, 13551, 13552, 13553, 13555, 13556, 13559, 13563, 13566,
13576, 13583, 13592, 13594, 13613, 13618, 13637, 13656, 13658, 13673,
13691, 13695, 13704, 13705, 13706, 13726, 13738, 13739, 13750, 13758,
6884, 6890, 6894, 6895, 6907, 6911, 6959, 7064, 9739, 9902, 10110, 10135,
10140, 10153, 10210, 10254, 10346, 10375, 10545, 10716, 10846, 11174,
11322, 11365, 11451, 11494, 11521, 11677, 11837, 11959, 12047, 12097,
12193, 12297, 12298, 12301, 12340, 12354, 12416, 12495, 13058, 13223,
13361, 13525, 13526, 13527, 13528, 13529, 13530, 13531, 13532, 13533,
13547, 13551, 13552, 13553, 13555, 13556, 13559, 13563, 13566, 13576,
13583, 13592, 13594, 13613, 13618, 13637, 13656, 13658, 13673, 13691,
13695, 13704, 13705, 13706, 13726, 13738, 13739, 13743, 13750, 13758,
13760, 13761, 13775, 13786, 13787, 13792, 13806, 13824, 13840, 13841,
13844, 13846, 13851, 13852, 13854, 13871, 13872, 13873, 13879, 13883,
13884, 13885, 13886, 13892, 13895, 13908, 13910, 13911, 13912, 13913,
@ -92,7 +92,8 @@ Version 2.16
* Optimized expf for x86-32 and x86-64. Implemented by Liubov Dmitrieva.
* More optimized functions for PowerPC. Implemented by Adhemerval Zanella.
* More optimized functions for PowerPC. Implemented by Adhemerval Zanella
and Will Schmidt.
* More optimized functions for SPARC. Implemented by David S. Miller.
@ -110,6 +111,11 @@ Version 2.16
/lib/ld-linux.so.3 dynamic linker used for the base EABI.
* Support for CRIS has been removed from ports.
* A new class of installed header has been documented for low-level
platform-specific functionality. PowerPC added the first instance with a
function to provide time base register access. Contributed by Tulio
Magno Quites Machado Filho.
Version 2.15

3
manual/Makefile
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@ -45,7 +45,8 @@ chapters = $(addsuffix .texi, \
resource setjmp signal startup process job nss \
users sysinfo conf crypt debug)
add-chapters = $(wildcard $(foreach d, $(add-ons), ../$d/$d.texi))
appendices = lang.texi header.texi install.texi maint.texi contrib.texi
appendices = lang.texi header.texi install.texi maint.texi platform.texi \
contrib.texi
licenses = freemanuals.texi lgpl-2.1.texi fdl-1.3.texi
-include $(objpfx)texis

2
manual/contrib.texi
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@ -1,4 +1,4 @@
@node Contributors, Free Manuals, Maintenance, Top
@node Contributors, Free Manuals, Platform, Top
@c %MENU% Who wrote what parts of the GNU C Library
@appendix Contributors to @theglibc{}

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manual/maint.texi
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@ -1,4 +1,4 @@
@node Maintenance, Contributors, Installation, Top
@node Maintenance, Platform, Installation, Top
@c %MENU% How to enhance and port the GNU C Library
@appendix Library Maintenance
@ -104,6 +104,85 @@ This variable is used for secondary object files needed to build
@code{others} or @code{tests}.
@end table
@menu
* Platform: Adding Platform-specific. Adding platform-specific
features.
@end menu
@node Adding Platform-specific
@appendixsubsec Platform-specific types, macros and functions
It's sometimes necessary to provide nonstandard, platform-specific
features to developers. The C library is traditionally the
lowest library layer, so it makes sense for it to provide these
low-level features. However, including these features in the C
library may be a disadvantage if another package provides them
as well as there will be two conflicting versions of them. Also,
the features won't be available to projects that do not use
@theglibc{} but use other GNU tools, like GCC.
The current guidelines are:
@itemize @bullet
@item
If the header file provides features that only make sense on a particular
machine architecture and have nothing to do with an operating system, then
the features should ultimately be provided as GCC built-in functions. Until
then, @theglibc{} may provide them in the header file. When the GCC built-in
functions become available, those provided in the header file should be made
conditionally available prior to the GCC version in which the built-in
function was made available.
@item
If the header file provides features that are specific to an operating system,
both GCC and @theglibc{} could provide it, but @theglibc{} is preferred
as it already has a lot of information about the operating system.
@item
If the header file provides features that are specific to an operating system
but used by @theglibc{}, then @theglibc{} should provide them.
@end itemize
The general solution for providing low-level features is to export them as
follows:
@itemize @bullet
@item
A nonstandard, low-level header file that defines macros and inline
functions should be called @file{sys/platform/@var{name}.h}.
@item
Each header file's name should include the platform name, to avoid
users thinking there is anything in common between different the
header files for different platforms. For example, a
@file{sys/platform/@var{arch}.h} name such as
@file{sys/platform/ppc.h} is better than @file{sys/platform.h}.
@item
A platform-specific header file provided by @theglibc{} should coordinate
with GCC such that compiler built-in versions of the functions and macros are
preferred if available. This means that user programs will only ever need to
include @file{sys/platform/@var{arch}.h}, keeping the same names of types,
macros, and functions for convenience and portability.
@item
Each included symbol must have the prefix @code{__@var{arch}_}, such as
@code{__ppc_get_timebase}.
@end itemize
The easiest way to provide a header file is to add it to the
@code{sysdep_headers} variable. For example, the combination of
Linux-specific header files on PowerPC could be provided like this:
@smallexample
sysdep_headers += sys/platform/ppc.h
@end smallexample
Then ensure that you have added a @file{sys/platform/ppc.h}
header file in the machine-specific directory, e.g.,
@file{sysdeps/powerpc/sys/platform/ppc.h}.
@node Porting
@appendixsec Porting @theglibc{}

28
manual/platform.texi Normal file
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@ -0,0 +1,28 @@
@node Platform, Contributors, Maintenance, Top
@c %MENU% Describe all platform-specific facilities provided
@appendix Platform-specific facilities
@Theglibc{} can provide machine-specific functionality.
@menu
* PowerPC:: Facilities Specific to the PowerPC Architecture
@end menu
@node PowerPC
@appendixsec PowerPC-specific Facilities
Facilities specific to PowerPC that are not specific to a particular
operating system are declared in @file{sys/platform/ppc.h}.
@deftypefun {uint64_t} __ppc_get_timebase (void)
Read the current value of the Time Base Register.
The @dfn{Time Base Register} is a 64-bit register that stores a monotonically
incremented value updated at a system-dependent frequency that may be
different from the processor frequency. More information is available in
@cite{Power ISA 2.06b - Book II - Section 5.2}.
@code{__ppc_get_timebase} uses the processor's time base facility directly
without requiring assistance from the operating system, so it is very
efficient.
@end deftypefun

5
sysdeps/powerpc/Makefile
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@ -26,3 +26,8 @@ gen-as-const-headers += rtld-global-offsets.sym
# get offset to __locale_struct.__ctype_tolower
gen-as-const-headers += locale-defines.sym
endif
ifeq ($(subdir),misc)
sysdep_headers += sys/platform/ppc.h
tests += test-gettimebase
endif

47
sysdeps/powerpc/sys/platform/ppc.h Normal file
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@ -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 */

46
sysdeps/powerpc/test-gettimebase.c Normal file
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@ -0,0 +1,46 @@
/* Check __ppc_get_timebase() for architecture changes
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/>. */
/* Test if __ppc_get_timebase() is compatible with the current processor and if
it's changing between reads. A read failure might indicate a Power ISA or
binutils change. */
#include <inttypes.h>
#include <stdio.h>
#include <sys/platform/ppc.h>
static int
do_test (void)
{
uint64_t t1, t2, t3;
t1 = __ppc_get_timebase ();
printf ("Time Base = %"PRIu64"\n", t1);
t2 = __ppc_get_timebase ();
printf ("Time Base = %"PRIu64"\n", t2);
t3 = __ppc_get_timebase ();
printf ("Time Base = %"PRIu64"\n", t3);
if (t1 != t2 && t1 != t3 && t2 != t3)
return 0;
printf ("Fail: timebase reads should always be different.");
return 1;
}
#define TEST_FUNCTION do_test ()
#include "../test-skeleton.c"