glibc/manual
Joseph Myers 81325b12b1 Add _Float128 function aliases.
This patch adds support for *f128 function aliases on platforms where
long double has the binary128 format (and thus GCC 7 provides the
_Float128 type with the same ABI as long double but as a distinct type
in terms of C type compatibility).  This is the same API as provided
in glibc 2.26 for powerpc64le / x86_64 / x86 / ia64 where _Float128
has a different format from long double, with the bulk of the API
coming from TS 18661-3.  All the functions alias the corresponding
long double functions, and __* function names are not provided since
those are only needed once for each floating-point format, not more
than once for different types with the same format (so for example,
-ffinite-math-only maps foof128 to __fool_finite, while type-generic
macros end up calling e.g. __issignalingl for _Float128 arguments on
such platforms).

The preparation for this feature was done in previous patches, so this
one just needs to add the relevant makefile and header definitions,
and update macro definitions of libm_alias_ldouble_other_r, to turn on
the feature, and update documentation and ABI baselines.

Tested (a) for x86_64, (b) for aarch64, (c) with build-many-glibcs.py
with both GCC 6 and GCC 7.

	* sysdeps/ieee754/ldbl-128/Makeconfig: New file.
	* sysdeps/ieee754/ldbl-128/bits/floatn.h: Likewise.
	* sysdeps/ieee754/ldbl-128/float128-abi.h: Likewise.
	* sysdeps/generic/libm-alias-ldouble.h: Include <bits/floatn.h>.
	[__HAVE_FLOAT128 && !__HAVE_DISTINCT_FLOAT128]
	(libm_alias_ldouble_other_r): Also create _Float128 alias.
	* sysdeps/ieee754/ldbl-opt/libm-alias-ldouble.h: Include
	<bits/floatn.h>.
	[__HAVE_FLOAT128 && !__HAVE_DISTINCT_FLOAT128]
	(libm_alias_ldouble_other_r): Also create _Float128 alias.
	* manual/math.texi (Mathematics): Document additional architecture
	support for _Float128.
	* sysdeps/unix/sysv/linux/aarch64/libc.abilist: Update.
	* sysdeps/unix/sysv/linux/aarch64/libm.abilist: Likewise.
	* sysdeps/unix/sysv/linux/alpha/libc.abilist: Likewise.
	* sysdeps/unix/sysv/linux/alpha/libm.abilist: Likewise.
	* sysdeps/unix/sysv/linux/mips/mips64/libm.abilist: Likewise.
	* sysdeps/unix/sysv/linux/mips/mips64/n32/libc.abilist: Likewise.
	* sysdeps/unix/sysv/linux/mips/mips64/n64/libc.abilist: Likewise.
	* sysdeps/unix/sysv/linux/s390/s390-32/libc.abilist: Likewise.
	* sysdeps/unix/sysv/linux/s390/s390-32/libm.abilist: Likewise.
	* sysdeps/unix/sysv/linux/s390/s390-64/libc.abilist: Likewise.
	* sysdeps/unix/sysv/linux/s390/s390-64/libm.abilist: Likewise.
	* sysdeps/unix/sysv/linux/sparc/sparc32/libc.abilist: Likewise.
	* sysdeps/unix/sysv/linux/sparc/sparc32/libm.abilist: Likewise.
	* sysdeps/unix/sysv/linux/sparc/sparc64/libc.abilist: Likewise.
	* sysdeps/unix/sysv/linux/sparc/sparc64/libm.abilist: Likewise.
2017-10-18 17:37:18 +00:00
..
examples Update copyright dates with scripts/update-copyrights. 2017-01-01 00:14:16 +00:00
argp.texi manual: Complete @standards in argp.texi. 2017-06-16 01:19:30 -07:00
arith.texi Obsolete matherr, _LIB_VERSION, libieee.a. 2017-08-21 17:45:10 +00:00
charset.texi manual: Replace summary.awk with summary.pl. 2017-06-15 21:26:20 -07:00
check-safety.sh Update copyright dates with scripts/update-copyrights. 2017-01-01 00:14:16 +00:00
conf.texi manual: Replace summary.awk with summary.pl. 2017-06-15 21:26:20 -07:00
contrib.texi Remove Banner mechanism. 2017-09-22 17:43:42 +00:00
creature.texi manual: Complete @standards in creature.texi. 2017-07-27 03:21:56 -07:00
crypt.texi manual: Replace summary.awk with summary.pl. 2017-06-15 21:26:20 -07:00
ctype.texi manual: Replace summary.awk with summary.pl. 2017-06-15 21:26:20 -07:00
debug.texi manual: Replace summary.awk with summary.pl. 2017-06-15 21:26:20 -07:00
dir
errno.texi manual: Replace summary.awk with summary.pl. 2017-06-15 21:26:20 -07:00
fdl-1.3.texi BZ#13738: Switch manual to FDL 1.3. 2012-02-24 12:58:10 -08:00
filesys.texi manual: Replace summary.awk with summary.pl. 2017-06-15 21:26:20 -07:00
freemanuals.texi Update to canonical freemanuals.texi file. 2013-09-24 14:06:56 -07:00
getopt.texi manual: Replace summary.awk with summary.pl. 2017-06-15 21:26:20 -07:00
header.texi manual: Replace summary.awk with summary.pl. 2017-06-15 21:26:20 -07:00
install-plain.texi BZ #15941: Fix INSTALL file regeneration failure with makeinfo 5.x 2013-12-05 09:58:20 +05:30
install.texi Remove add-ons mechanism. 2017-10-05 15:58:13 +00:00
intro.texi manual: fix typo in the introduction 2016-05-19 23:22:59 -04:00
io.texi Clean up glibc manual references to "GNU system" (bug 6911). 2012-03-08 01:27:38 +00:00
ipc.texi manual/ipc.texi: Fix AC-safety notes. 2014-04-08 17:12:15 -04:00
job.texi manual: Replace summary.awk with summary.pl. 2017-06-15 21:26:20 -07:00
lang.texi manual: Rewrite the section on widths of integer types. 2017-08-10 20:28:28 -07:00
lgpl-2.1.texi Use canonical FSF .texi files for LGPL and FDL texts. 2011-06-06 16:16:55 -07:00
libc-texinfo.sh Remove add-ons mechanism. 2017-10-05 15:58:13 +00:00
libc.texinfo Update copyright dates not handled by scripts/update-copyrights. 2017-01-01 00:26:24 +00:00
libcbook.texi
libdl.texi * manual/libdl.texi: New. 2014-01-31 23:23:59 -02:00
libm-err-tab.pl Prepare the manual to display math errors for float128 functions 2017-06-23 10:31:09 -03:00
llio.texi posix: Add p{read,write}v2 RWF_NOWAIT flag (BZ#21738) 2017-07-11 11:06:44 -03:00
locale.texi manual: Replace summary.awk with summary.pl. 2017-06-15 21:26:20 -07:00
macros.texi manual: Replace summary.awk with summary.pl. 2017-06-15 21:26:20 -07:00
maint.texi Remove add-ons mechanism. 2017-10-05 15:58:13 +00:00
Makefile Remove add-ons mechanism. 2017-10-05 15:58:13 +00:00
math.texi Add _Float128 function aliases. 2017-10-18 17:37:18 +00:00
memory.texi malloc: Remove check_action variable [BZ #21754] 2017-08-30 20:08:34 +02:00
message.texi manual: Replace summary.awk with summary.pl. 2017-06-15 21:26:20 -07:00
nss.texi Remove compat from DEFAULT_CONFIG lookup strings 2017-09-12 10:21:48 -07:00
nsswitch.texi
pattern.texi manual: Replace summary.awk with summary.pl. 2017-06-15 21:26:20 -07:00
pipe.texi manual: Replace summary.awk with summary.pl. 2017-06-15 21:26:20 -07:00
platform.texi PowerPC: Extend Program Priority Register support 2015-08-19 17:43:26 -03:00
probes.texi malloc: Remove check_action variable [BZ #21754] 2017-08-30 20:08:34 +02:00
process.texi manual: Replace summary.awk with summary.pl. 2017-06-15 21:26:20 -07:00
README.pretty-printers Remove obsolete notes at top level of source tree. 2017-09-01 08:04:22 -04:00
README.tunables Remove obsolete notes at top level of source tree. 2017-09-01 08:04:22 -04:00
resource.texi manual: Replace summary.awk with summary.pl. 2017-06-15 21:26:20 -07:00
search.texi manual: Replace summary.awk with summary.pl. 2017-06-15 21:26:20 -07:00
setjmp.texi manual: Document getcontext uc_stack value on Linux [BZ #759] 2017-08-08 16:16:43 -03:00
signal.texi manual: Replace summary.awk with summary.pl. 2017-06-15 21:26:20 -07:00
socket.texi manual: Replace summary.awk with summary.pl. 2017-06-15 21:26:20 -07:00
startup.texi manual: Replace summary.awk with summary.pl. 2017-06-15 21:26:20 -07:00
stdio-fp.c
stdio.texi manual: Replace summary.awk with summary.pl. 2017-06-15 21:26:20 -07:00
string.texi manual: Complete @standards in string.texi. 2017-06-16 01:23:17 -07:00
summary.pl manual: Replace summary.awk with summary.pl. 2017-06-15 21:26:20 -07:00
sysinfo.texi manual: Replace summary.awk with summary.pl. 2017-06-15 21:26:20 -07:00
syslog.texi manual: Replace summary.awk with summary.pl. 2017-06-15 21:26:20 -07:00
terminal.texi manual: Replace summary.awk with summary.pl. 2017-06-15 21:26:20 -07:00
texinfo.tex Update miscellaneous files from upstream sources. 2016-12-21 16:05:55 +00:00
texis.awk
threads.texi manual: Replace summary.awk with summary.pl. 2017-06-15 21:26:20 -07:00
time.texi manual: Replace summary.awk with summary.pl. 2017-06-15 21:26:20 -07:00
tsort.awk Update copyright dates with scripts/update-copyrights. 2017-01-01 00:14:16 +00:00
tunables.texi Add thunderx2t99 and thunderx2t99p1 CPU names to tunables list 2017-09-08 11:02:09 -07:00
users.texi manual: Replace summary.awk with summary.pl. 2017-06-15 21:26:20 -07:00
xtract-typefun.awk Make shebang interpreter directives consistent 2016-01-07 04:03:21 -05:00

			TUNABLE FRAMEWORK
			=================

Tunables is a feature in the GNU C Library that allows application authors and
distribution maintainers to alter the runtime library behaviour to match their
workload.

The tunable framework allows modules within glibc to register variables that
may be tweaked through an environment variable.  It aims to enforce a strict
namespace rule to bring consistency to naming of these tunable environment
variables across the project.  This document is a guide for glibc developers to
add tunables to the framework.

ADDING A NEW TUNABLE
--------------------

The TOP_NAMESPACE macro is defined by default as 'glibc'.  If distributions
intend to add their own tunables, they should do so in a different top
namespace by overriding the TOP_NAMESPACE macro for that tunable.  Downstream
implementations are discouraged from using the 'glibc' top namespace for
tunables they don't already have consensus to push upstream.

There are three steps to adding a tunable:

1. Add a tunable to the list and fully specify its properties:

For each tunable you want to add, make an entry in elf/dl-tunables.list.  The
format of the file is as follows:

TOP_NAMESPACE {
  NAMESPACE1 {
    TUNABLE1 {
      # tunable attributes, one per line
    }
    # A tunable with default attributes, i.e. string variable.
    TUNABLE2
    TUNABLE3 {
      # its attributes
    }
  }
  NAMESPACE2 {
    ...
  }
}

The list of allowed attributes are:

- type:			Data type.  Defaults to STRING.  Allowed types are:
			INT_32, UINT_64, SIZE_T and STRING.  Numeric types may
			be in octal or hexadecimal format too.

- minval:		Optional minimum acceptable value.  For a string type
			this is the minimum length of the value.

- maxval:		Optional maximum acceptable value.  For a string type
			this is the maximum length of the value.

- default:		Specify an optional default value for the tunable.

- env_alias:		An alias environment variable

- security_level:	Specify security level of the tunable.  Valid values:

			SXID_ERASE: (default) Don't read for AT_SECURE binaries and
				    removed so that child processes can't read it.
			SXID_IGNORE: Don't read for AT_SECURE binaries, but retained for
				     non-AT_SECURE subprocesses.
			NONE: Read all the time.

2. Use TUNABLE_GET/TUNABLE_SET to get and set tunables.

3. OPTIONAL: If tunables in a namespace are being used multiple times within a
   specific module, set the TUNABLE_NAMESPACE macro to reduce the amount of
   typing.

GETTING AND SETTING TUNABLES
----------------------------

When the TUNABLE_NAMESPACE macro is defined, one may get tunables in that
module using the TUNABLE_GET macro as follows:

  val = TUNABLE_GET (check, int32_t, TUNABLE_CALLBACK (check_callback))

where 'check' is the tunable name, 'int32_t' is the C type of the tunable and
'check_callback' is the function to call if the tunable got initialized to a
non-default value.  The macro returns the value as type 'int32_t'.

The callback function should be defined as follows:

  void
  TUNABLE_CALLBACK (check_callback) (int32_t *valp)
  {
  ...
  }

where it can expect the tunable value to be passed in VALP.

Tunables in the module can be updated using:

  TUNABLE_SET (check, int32_t, val)

where 'check' is the tunable name, 'int32_t' is the C type of the tunable and
'val' is a value of same type.

To get and set tunables in a different namespace from that module, use the full
form of the macros as follows:

  val = TUNABLE_GET_FULL (glibc, tune, hwcap_mask, uint64_t, NULL)

  TUNABLE_SET_FULL (glibc, tune, hwcap_mask, uint64_t, val)

where 'glibc' is the top namespace, 'tune' is the tunable namespace and the
remaining arguments are the same as the short form macros.

When TUNABLE_NAMESPACE is not defined in a module, TUNABLE_GET is equivalent to
TUNABLE_GET_FULL, so you will need to provide full namespace information for
both macros.  Likewise for TUNABLE_SET and TUNABLE_SET_FULL.

** IMPORTANT NOTE **

The tunable list is set as read-only after the dynamic linker relocates itself,
so setting tunable values must be limited only to tunables within the dynamic
linker, that too before relocation.

FUTURE WORK
-----------

The framework currently only allows a one-time initialization of variables
through environment variables and in some cases, modification of variables via
an API call.  A future goals for this project include:

- Setting system-wide and user-wide defaults for tunables through some
  mechanism like a configuration file.

- Allow tweaking of some tunables at runtime