glibc/manual
Joseph Myers 0d93b7fd7c Add _Float64, _Float32x function aliases.
This patch continues filling out TS 18661-3 support by adding *f64 and
*f32x function aliases, supporting _Float64 and _Float32x, as aliases
for double functions.  These types are supported for all glibc
configurations.  The API corresponds exactly to that for _Float128 and
_Float64x.  _Float32 aliases to float functions remain to be added in
subsequent patches to complete this process (then there are a few
miscellaneous functions in TS 18661-3 to implement that aren't simply
versions of existing functions for new types).

The patch enables the feature in bits/floatn-common.h, adds symbol
versions and documentation with updates to ABI baselines, and arranges
for the libm functions for the new types to be tested.  As with the
_Float64x changes there are some x86 ulps updates because of header
inlines not used for the new types (and one other change to the
non-multiarch libm-test-ulps, which I suppose comes from using a
different compiler version / configuration from when it was last
regenerated).

Tested for x86_64 and x86, and with build-many-glibcs.py, with both
GCC 6 and GCC 7.

	* bits/floatn-common.h (__HAVE_FLOAT64): Define to 1.
	(__HAVE_FLOAT32X): Likewise.
	* manual/math.texi (Mathematics): Document support for _Float64
	and _Float32x.
	* math/Makefile (test-types): Add float64 and float32x.
	* math/Versions (GLIBC_2.27): Add _Float64 and _Float32x
	functions.
	* stdlib/Versions (GLIBC_2.27): Likewise.
	* wcsmbs/Versions (GLIBC_2.27): Likewise.
	* 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/arm/libc.abilist: Likewise.
	* sysdeps/unix/sysv/linux/arm/libm.abilist: Likewise.
	* sysdeps/unix/sysv/linux/hppa/libc.abilist: Likewise.
	* sysdeps/unix/sysv/linux/hppa/libm.abilist: Likewise.
	* sysdeps/unix/sysv/linux/i386/libc.abilist: Likewise.
	* sysdeps/unix/sysv/linux/i386/libm.abilist: Likewise.
	* sysdeps/unix/sysv/linux/ia64/libc.abilist: Likewise.
	* sysdeps/unix/sysv/linux/ia64/libm.abilist: Likewise.
	* sysdeps/unix/sysv/linux/m68k/coldfire/libc.abilist: Likewise.
	* sysdeps/unix/sysv/linux/m68k/coldfire/libm.abilist: Likewise.
	* sysdeps/unix/sysv/linux/m68k/m680x0/libc.abilist: Likewise.
	* sysdeps/unix/sysv/linux/m68k/m680x0/libm.abilist: Likewise.
	* sysdeps/unix/sysv/linux/microblaze/libc.abilist: Likewise.
	* sysdeps/unix/sysv/linux/microblaze/libm.abilist: Likewise.
	* sysdeps/unix/sysv/linux/mips/mips32/fpu/libc.abilist: Likewise.
	* sysdeps/unix/sysv/linux/mips/mips32/libm.abilist: Likewise.
	* sysdeps/unix/sysv/linux/mips/mips32/nofpu/libc.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/nios2/libc.abilist: Likewise.
	* sysdeps/unix/sysv/linux/nios2/libm.abilist: Likewise.
	* sysdeps/unix/sysv/linux/powerpc/powerpc32/fpu/libc.abilist:
	Likewise.
	* sysdeps/unix/sysv/linux/powerpc/powerpc32/fpu/libm.abilist:
	Likewise.
	* sysdeps/unix/sysv/linux/powerpc/powerpc32/nofpu/libc.abilist:
	Likewise.
	* sysdeps/unix/sysv/linux/powerpc/powerpc32/nofpu/libm.abilist:
	Likewise.
	* sysdeps/unix/sysv/linux/powerpc/powerpc64/libc-le.abilist:
	Likewise.
	* sysdeps/unix/sysv/linux/powerpc/powerpc64/libc.abilist:
	Likewise.
	* sysdeps/unix/sysv/linux/powerpc/powerpc64/libm-le.abilist:
	Likewise.
	* sysdeps/unix/sysv/linux/powerpc/powerpc64/libm.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/sh/libc.abilist: Likewise.
	* sysdeps/unix/sysv/linux/sh/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.
	* sysdeps/unix/sysv/linux/tile/tilegx/tilegx32/libc.abilist:
	Likewise.
	* sysdeps/unix/sysv/linux/tile/tilegx/tilegx32/libm.abilist:
	Likewise.
	* sysdeps/unix/sysv/linux/tile/tilegx/tilegx64/libc.abilist:
	Likewise.
	* sysdeps/unix/sysv/linux/tile/tilegx/tilegx64/libm.abilist:
	Likewise.
	* sysdeps/unix/sysv/linux/tile/tilepro/libc.abilist: Likewise.
	* sysdeps/unix/sysv/linux/tile/tilepro/libm.abilist: Likewise.
	* sysdeps/unix/sysv/linux/x86_64/64/libc.abilist: Likewise.
	* sysdeps/unix/sysv/linux/x86_64/64/libm.abilist: Likewise.
	* sysdeps/unix/sysv/linux/x86_64/x32/libc.abilist: Likewise.
	* sysdeps/unix/sysv/linux/x86_64/x32/libm.abilist: Likewise.
	* sysdeps/i386/fpu/libm-test-ulps: Likewise.
	* sysdeps/i386/i686/fpu/multiarch/libm-test-ulps: Likewise.
2017-12-06 00:58:03 +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 aarch64: Document _SC_LEVEL1_DCACHE_LINESIZE caveat 2017-10-23 20:23:35 +05:30
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 .. 2005-11-21 15:45:19 +00:00
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: Document the linkat function 2017-11-04 00:28:37 +01:00
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 Add elision tunables 2017-12-05 17:48:48 -02:00
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 Linux: Add memfd_create system call wrapper 2017-11-23 10:00:40 +01:00
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 _Float64, _Float32x function aliases. 2017-12-06 00:58:03 +00:00
memory.texi Linux: Implement interfaces for memory protection keys 2017-12-05 15:20:35 +01:00
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: Update to mention ENODEV for ttyname and ttyname_r 2017-11-15 20:46:45 +01:00
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 elision tunables 2017-12-05 17:48:48 -02:00
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