INSTALL: Add a note for Intel CET status

[glibc.git] / manual / install.texi

@include macros.texi
@include pkgvers.texi

@ifclear plain
@node Installation, Maintenance, Library Summary, Top
@end ifclear

@c %MENU% How to install the GNU C Library
@appendix Installing @theglibc{}

Before you do anything else, you should read the FAQ at
@url{https://sourceware.org/glibc/wiki/FAQ}.  It answers common
questions and describes problems you may experience with compilation
and installation.

You will need recent versions of several GNU tools: definitely GCC and
GNU Make, and possibly others.  @xref{Tools for Compilation}, below.

@ifclear plain
@menu
* Configuring and compiling::   How to compile and test GNU libc.
* Running make install::        How to install it once you've got it
 compiled.
* Tools for Compilation::       You'll need these first.
* Linux::                       Specific advice for GNU/Linux systems.
* Reporting Bugs::              So they'll get fixed.
@end menu
@end ifclear

@node Configuring and compiling
@appendixsec Configuring and compiling @theglibc{}
@cindex configuring
@cindex compiling

@Theglibc{} cannot be compiled in the source directory.  You must build
it in a separate build directory.  For example, if you have unpacked
the @glibcadj{} sources in @file{/src/gnu/glibc-@var{version}},
create a directory
@file{/src/gnu/glibc-build} to put the object files in.  This allows
removing the whole build directory in case an error occurs, which is
the safest way to get a fresh start and should always be done.

From your object directory, run the shell script @file{configure} located
at the top level of the source tree.  In the scenario above, you'd type

@smallexample
$ ../glibc-@var{version}/configure @var{args@dots{}}
@end smallexample

Please note that even though you're building in a separate build
directory, the compilation may need to create or modify files and
directories in the source directory.

@noindent
@code{configure} takes many options, but the only one that is usually
mandatory is @samp{--prefix}.  This option tells @code{configure}
where you want @theglibc{} installed.  This defaults to @file{/usr/local},
but the normal setting to install as the standard system library is
@samp{--prefix=/usr} for @gnulinuxsystems{} and @samp{--prefix=} (an
empty prefix) for @gnuhurdsystems{}.

It may also be useful to pass @samp{CC=@var{compiler}} and
@code{CFLAGS=@var{flags}} arguments to @code{configure}.  @code{CC}
selects the C compiler that will be used, and @code{CFLAGS} sets
optimization options for the compiler.  Any compiler options required
for all compilations, such as options selecting an ABI or a processor
for which to generate code, should be included in @code{CC}.  Options
that may be overridden by the @glibcadj{} build system for particular
files, such as for optimization and debugging, should go in
@code{CFLAGS}.  The default value of @code{CFLAGS} is @samp{-g -O2},
and @theglibc{} cannot be compiled without optimization, so if
@code{CFLAGS} is specified it must enable optimization.  For example:

@smallexample
$ ../glibc-@var{version}/configure CC="gcc -m32" CFLAGS="-O3"
@end smallexample

The following list describes all of the available options for
 @code{configure}:

@table @samp
@item --prefix=@var{directory}
Install machine-independent data files in subdirectories of
@file{@var{directory}}.  The default is to install in @file{/usr/local}.

@item --exec-prefix=@var{directory}
Install the library and other machine-dependent files in subdirectories
of @file{@var{directory}}.  The default is to the @samp{--prefix}
directory if that option is specified, or @file{/usr/local} otherwise.

@item --with-headers=@var{directory}
Look for kernel header files in @var{directory}, not
@file{/usr/include}.  @Theglibc{} needs information from the kernel's header
files describing the interface to the kernel.  @Theglibc{} will normally
look in @file{/usr/include} for them,
but if you specify this option, it will look in @var{DIRECTORY} instead.

This option is primarily of use on a system where the headers in
@file{/usr/include} come from an older version of @theglibc{}.  Conflicts can
occasionally happen in this case.  You can also use this option if you want to
compile @theglibc{} with a newer set of kernel headers than the ones found in
@file{/usr/include}.

@item --enable-kernel=@var{version}
This option is currently only useful on @gnulinuxsystems{}.  The
@var{version} parameter should have the form X.Y.Z and describes the
smallest version of the Linux kernel the generated library is expected
to support.  The higher the @var{version} number is, the less
compatibility code is added, and the faster the code gets.

@item --with-binutils=@var{directory}
Use the binutils (assembler and linker) in @file{@var{directory}}, not
the ones the C compiler would default to.  You can use this option if
the default binutils on your system cannot deal with all the constructs
in @theglibc{}.  In that case, @code{configure} will detect the
problem and suppress these constructs, so that the library will still be
usable, but functionality may be lost---for example, you can't build a
shared libc with old binutils.

@c disable static doesn't work currently
@c @item --disable-static
@c Don't build static libraries.  Static libraries aren't that useful these
@c days, but we recommend you build them in case you need them.

@item --disable-shared
Don't build shared libraries even if it is possible.  Not all systems
support shared libraries; you need ELF support and (currently) the GNU
linker.

@item --enable-static-pie
Enable static position independent executable (static PIE) support.
Static PIE is similar to static executable, but can be loaded at any
address without help from a dynamic linker.  All static programs as
well as static tests are built as static PIE, except for those marked
with no-pie.  The resulting glibc can be used with the GCC option,
-static-pie, which is available with GCC 8 or above, to create static
PIE.  This option also implies that glibc programs and tests are created
as dynamic position independent executables (PIE) by default.

@item --enable-cet
Enable Intel Control-flow Enforcement Technology (CET) support.  When
@theglibc{} is built with @option{--enable-cet}, the resulting library
is protected with indirect branch tracking (IBT) and shadow stack
(SHSTK)@.  When CET is enabled, @theglibc{} is compatible with all
existing executables and shared libraries.  This feature is currently
supported on i386, x86_64 and x32 with GCC 8 and binutils 2.29 or later.
Note that when CET is enabled, @theglibc{} requires CPUs capable of
multi-byte NOPs, like x86-64 processors as well as Intel Pentium Pro or
newer.

NOTE: @option{--enable-cet} has been tested for i686, x86_64 and x32
on non-CET processors.  @option{--enable-cet} has been tested for
x86_64 and x32 on CET SDVs, but Intel CET support hasn't been validated
for i686.

@item --disable-profile
Don't build libraries with profiling information.  You may want to use
this option if you don't plan to do profiling.

@item --enable-static-nss
Compile static versions of the NSS (Name Service Switch) libraries.
This is not recommended because it defeats the purpose of NSS; a program
linked statically with the NSS libraries cannot be dynamically
reconfigured to use a different name database.

@item --enable-hardcoded-path-in-tests
By default, dynamic tests are linked to run with the installed C library.
This option hardcodes the newly built C library path in dynamic tests
so that they can be invoked directly.

@item --disable-timezone-tools
By default, timezone related utilities (@command{zic}, @command{zdump},
and @command{tzselect}) are installed with @theglibc{}.  If you are building
these independently (e.g. by using the @samp{tzcode} package), then this
option will allow disabling the install of these.

Note that you need to make sure the external tools are kept in sync with
the versions that @theglibc{} expects as the data formats may change over
time.  Consult the @file{timezone} subdirectory for more details.

@item --enable-stack-protector
@itemx --enable-stack-protector=strong
@itemx --enable-stack-protector=all
Compile the C library and all other parts of the glibc package
(including the threading and math libraries, NSS modules, and
transliteration modules) using the GCC @option{-fstack-protector},
@option{-fstack-protector-strong} or @option{-fstack-protector-all}
options to detect stack overruns.  Only the dynamic linker and a small
number of routines called directly from assembler are excluded from this
protection.

@item --enable-bind-now
Disable lazy binding for installed shared objects.  This provides
additional security hardening because it enables full RELRO and a
read-only global offset table (GOT), at the cost of slightly increased
program load times.

@pindex pt_chown
@findex grantpt
@item --enable-pt_chown
The file @file{pt_chown} is a helper binary for @code{grantpt}
(@pxref{Allocation, Pseudo-Terminals}) that is installed setuid root to
fix up pseudo-terminal ownership.  It is not built by default because
systems using the Linux kernel are commonly built with the @code{devpts}
filesystem enabled and mounted at @file{/dev/pts}, which manages
pseudo-terminal ownership automatically.  By using
@samp{--enable-pt_chown}, you may build @file{pt_chown} and install it
setuid and owned by @code{root}.  The use of @file{pt_chown} introduces
additional security risks to the system and you should enable it only if
you understand and accept those risks.

@item --disable-werror
By default, @theglibc{} is built with @option{-Werror}.  If you wish
to build without this option (for example, if building with a newer
version of GCC than this version of @theglibc{} was tested with, so
new warnings cause the build with @option{-Werror} to fail), you can
configure with @option{--disable-werror}.

@item --disable-mathvec
By default for x86_64, @theglibc{} is built with the vector math library.
Use this option to disable the vector math library.

@item --enable-tunables
Tunables support allows additional library parameters to be customized at
runtime.  This feature is enabled by default.  This option can take the
following values:

@table @code
@item yes
This is the default if no option is passed to configure. This enables tunables
and selects the default frontend (currently @samp{valstring}).

@item no
This option disables tunables.

@item valstring
This enables tunables and selects the @samp{valstring} frontend for tunables.
This frontend allows users to specify tunables as a colon-separated list in a
single environment variable @env{GLIBC_TUNABLES}.
@end table

@item --enable-obsolete-nsl
By default, libnsl is only built as shared library for backward
compatibility and the NSS modules libnss_compat, libnss_nis and
libnss_nisplus are not built at all.
Use this option to enable libnsl with all depending NSS modules and
header files.

@item --disable-crypt
Do not install the passphrase-hashing library @file{libcrypt} or the
header file @file{crypt.h}.  @file{unistd.h} will still declare the
function @code{crypt}.  Using this option does not change the set of
programs that may need to be linked with @option{-lcrypt}; it only
means that @theglibc{} will not provide that library.

This option is for hackers and distributions experimenting with
independently-maintained implementations of libcrypt.  It may become
the default in a future release.

@item --disable-experimental-malloc
By default, a per-thread cache is enabled in @code{malloc}.  While
this cache can be disabled on a per-application basis using tunables
(set glibc.malloc.tcache_count to zero), this option can be used to
remove it from the build completely.

@item --build=@var{build-system}
@itemx --host=@var{host-system}
These options are for cross-compiling.  If you specify both options and
@var{build-system} is different from @var{host-system}, @code{configure}
will prepare to cross-compile @theglibc{} from @var{build-system} to be used
on @var{host-system}.  You'll probably need the @samp{--with-headers}
option too, and you may have to override @var{configure}'s selection of
the compiler and/or binutils.

If you only specify @samp{--host}, @code{configure} will prepare for a
native compile but use what you specify instead of guessing what your
system is.  This is most useful to change the CPU submodel.  For example,
if @code{configure} guesses your machine as @code{i686-pc-linux-gnu} but
you want to compile a library for 586es, give
@samp{--host=i586-pc-linux-gnu} or just @samp{--host=i586-linux} and add
the appropriate compiler flags (@samp{-mcpu=i586} will do the trick) to
@code{CC}.

If you specify just @samp{--build}, @code{configure} will get confused.

@item --with-pkgversion=@var{version}
Specify a description, possibly including a build number or build
date, of the binaries being built, to be included in
@option{--version} output from programs installed with @theglibc{}.
For example, @option{--with-pkgversion='FooBar GNU/Linux glibc build
123'}.  The default value is @samp{GNU libc}.

@item --with-bugurl=@var{url}
Specify the URL that users should visit if they wish to report a bug,
to be included in @option{--help} output from programs installed with
@theglibc{}.  The default value refers to the main bug-reporting
information for @theglibc{}.
@end table

To build the library and related programs, type @code{make}.  This will
produce a lot of output, some of which may look like errors from
@code{make} but aren't.  Look for error messages from @code{make}
containing @samp{***}.  Those indicate that something is seriously wrong.

The compilation process can take a long time, depending on the
configuration and the speed of your machine.  Some complex modules may
take a very long time to compile, as much as several minutes on slower
machines.  Do not panic if the compiler appears to hang.

If you want to run a parallel make, simply pass the @samp{-j} option
with an appropriate numeric parameter to @code{make}.  You need a recent
GNU @code{make} version, though.

To build and run test programs which exercise some of the library
facilities, type @code{make check}.  If it does not complete
successfully, do not use the built library, and report a bug after
verifying that the problem is not already known.  @xref{Reporting Bugs},
for instructions on reporting bugs.  Note that some of the tests assume
they are not being run by @code{root}.  We recommend you compile and
test @theglibc{} as an unprivileged user.

Before reporting bugs make sure there is no problem with your system.
The tests (and later installation) use some pre-existing files of the
system such as @file{/etc/passwd}, @file{/etc/nsswitch.conf} and others.
These files must all contain correct and sensible content.

Normally, @code{make check} will run all the tests before reporting
all problems found and exiting with error status if any problems
occurred.  You can specify @samp{stop-on-test-failure=y} when running
@code{make check} to make the test run stop and exit with an error
status immediately when a failure occurs.

The @glibcadj{} pretty printers come with their own set of scripts for testing,
which run together with the rest of the testsuite through @code{make check}.
These scripts require the following tools to run successfully:

@itemize @bullet
@item
Python 2.7.6/3.4.3 or later

Python is required for running the printers' test scripts.

@item PExpect 4.0

The printer tests drive GDB through test programs and compare its output
to the printers'.  PExpect is used to capture the output of GDB, and should be
compatible with the Python version in your system.

@item
GDB 7.8 or later with support for Python 2.7.6/3.4.3 or later

GDB itself needs to be configured with Python support in order to use the
pretty printers.  Notice that your system having Python available doesn't imply
that GDB supports it, nor that your system's Python and GDB's have the same
version.
@end itemize

@noindent
If these tools are absent, the printer tests will report themselves as
@code{UNSUPPORTED}.  Notice that some of the printer tests require @theglibc{}
to be compiled with debugging symbols.

To format the @cite{GNU C Library Reference Manual} for printing, type
@w{@code{make dvi}}.  You need a working @TeX{} installation to do
this.  The distribution builds the on-line formatted version of the
manual, as Info files, as part of the build process.  You can build
them manually with @w{@code{make info}}.

The library has a number of special-purpose configuration parameters
which you can find in @file{Makeconfig}.  These can be overwritten with
the file @file{configparms}.  To change them, create a
@file{configparms} in your build directory and add values as appropriate
for your system.  The file is included and parsed by @code{make} and has
to follow the conventions for makefiles.

It is easy to configure @theglibc{} for cross-compilation by
setting a few variables in @file{configparms}.  Set @code{CC} to the
cross-compiler for the target you configured the library for; it is
important to use this same @code{CC} value when running
@code{configure}, like this: @samp{configure @var{target}
CC=@var{target}-gcc}.  Set @code{BUILD_CC} to the compiler to use for programs
run on the build system as part of compiling the library.  You may need to
set @code{AR} to cross-compiling versions of @code{ar}
if the native tools are not configured to work with
object files for the target you configured for.  When cross-compiling
@theglibc{}, it may be tested using @samp{make check
test-wrapper="@var{srcdir}/scripts/cross-test-ssh.sh @var{hostname}"},
where @var{srcdir} is the absolute directory name for the main source
directory and @var{hostname} is the host name of a system that can run
the newly built binaries of @theglibc{}.  The source and build
directories must be visible at the same locations on both the build
system and @var{hostname}.

In general, when testing @theglibc{}, @samp{test-wrapper} may be set
to the name and arguments of any program to run newly built binaries.
This program must preserve the arguments to the binary being run, its
working directory and the standard input, output and error file
descriptors.  If @samp{@var{test-wrapper} env} will not work to run a
program with environment variables set, then @samp{test-wrapper-env}
must be set to a program that runs a newly built program with
environment variable assignments in effect, those assignments being
specified as @samp{@var{var}=@var{value}} before the name of the
program to be run.  If multiple assignments to the same variable are
specified, the last assignment specified must take precedence.
Similarly, if @samp{@var{test-wrapper} env -i} will not work to run a
program with an environment completely empty of variables except those
directly assigned, then @samp{test-wrapper-env-only} must be set; its
use has the same syntax as @samp{test-wrapper-env}, the only
difference in its semantics being starting with an empty set of
environment variables rather than the ambient set.


@node Running make install
@appendixsec Installing the C Library
@cindex installing

To install the library and its header files, and the Info files of the
manual, type @code{make install}.  This will
build things, if necessary, before installing them; however, you should
still compile everything first.  If you are installing @theglibc{} as your
primary C library, we recommend that you shut the system down to
single-user mode first, and reboot afterward.  This minimizes the risk
of breaking things when the library changes out from underneath.

@samp{make install} will do the entire job of upgrading from a
previous installation of @theglibc{} version 2.x.  There may sometimes
be headers
left behind from the previous installation, but those are generally
harmless.  If you want to avoid leaving headers behind you can do
things in the following order.

You must first build the library (@samp{make}), optionally check it
(@samp{make check}), switch the include directories and then install
(@samp{make install}).  The steps must be done in this order.  Not moving
the directory before install will result in an unusable mixture of header
files from both libraries, but configuring, building, and checking the
library requires the ability to compile and run programs against the old
library.  The new @file{/usr/include}, after switching the include
directories and before installing the library should contain the Linux
headers, but nothing else.  If you do this, you will need to restore
any headers from libraries other than @theglibc{} yourself after installing the
library.

You can install @theglibc{} somewhere other than where you configured
it to go by setting the @code{DESTDIR} GNU standard make variable on
the command line for @samp{make install}.  The value of this variable
is prepended to all the paths for installation.  This is useful when
setting up a chroot environment or preparing a binary distribution.
The directory should be specified with an absolute file name. Installing
with the @code{prefix} and @code{exec_prefix} GNU standard make variables
set is not supported.

@Theglibc{} includes a daemon called @code{nscd}, which you
may or may not want to run.  @code{nscd} caches name service lookups; it
can dramatically improve performance with NIS+, and may help with DNS as
well.

One auxiliary program, @file{/usr/libexec/pt_chown}, is installed setuid
@code{root} if the @samp{--enable-pt_chown} configuration option is used.
This program is invoked by the @code{grantpt} function; it sets the
permissions on a pseudoterminal so it can be used by the calling process.
If you are using a Linux kernel with the @code{devpts} filesystem enabled
and mounted at @file{/dev/pts}, you don't need this program.

After installation you might want to configure the timezone and locale
installation of your system.  @Theglibc{} comes with a locale
database which gets configured with @code{localedef}.  For example, to
set up a German locale with name @code{de_DE}, simply issue the command
@samp{localedef -i de_DE -f ISO-8859-1 de_DE}.  To configure all locales
that are supported by @theglibc{}, you can issue from your build directory the
command @samp{make localedata/install-locales}.

To configure the locally used timezone, set the @code{TZ} environment
variable.  The script @code{tzselect} helps you to select the right value.
As an example, for Germany, @code{tzselect} would tell you to use
@samp{TZ='Europe/Berlin'}.  For a system wide installation (the given
paths are for an installation with @samp{--prefix=/usr}), link the
timezone file which is in @file{/usr/share/zoneinfo} to the file
@file{/etc/localtime}.  For Germany, you might execute @samp{ln -s
/usr/share/zoneinfo/Europe/Berlin /etc/localtime}.

@node Tools for Compilation
@appendixsec Recommended Tools for Compilation
@cindex installation tools
@cindex tools, for installing library

We recommend installing the following GNU tools before attempting to
build @theglibc{}:

@itemize @bullet
@item
GNU @code{make} 4.0 or newer

@item
GCC 4.9 or newer

GCC 4.9 or higher is required.  In general it is recommended to use
the newest version of the compiler that is known to work for building
@theglibc{}, as newer compilers usually produce better code.  As of
release time, GCC 7.3 is the newest compiler verified to work to build
@theglibc{}.

For PowerPC 64-bits little-endian (powerpc64le), GCC 6.2 or higher is
required.  This compiler version is the first to provide the features
required for building @theglibc{} with support for @code{_Float128}.

For multi-arch support it is recommended to use a GCC which has been built with
support for GNU indirect functions.  This ensures that correct debugging
information is generated for functions selected by IFUNC resolvers.  This
support can either be enabled by configuring GCC with
@samp{--enable-gnu-indirect-function}, or by enabling it by default by setting
@samp{default_gnu_indirect_function} variable for a particular architecture in
the GCC source file @file{gcc/config.gcc}.

You can use whatever compiler you like to compile programs that use
@theglibc{}.

Check the FAQ for any special compiler issues on particular platforms.

@item
GNU @code{binutils} 2.25 or later

You must use GNU @code{binutils} (as and ld) to build @theglibc{}.
No other assembler or linker has the necessary functionality at the
moment. As of release time, GNU @code{binutils} 2.29.1 is the newest
verified to work to build @theglibc{}.

@item
GNU @code{texinfo} 4.7 or later

To correctly translate and install the Texinfo documentation you need
this version of the @code{texinfo} package.  Earlier versions do not
understand all the tags used in the document, and the installation
mechanism for the info files is not present or works differently.
As of release time, @code{texinfo} 6.5 is the newest verified to work
to build @theglibc{}.

@item
GNU @code{awk} 3.1.2, or higher

@code{awk} is used in several places to generate files.
Some @code{gawk} extensions are used, including the @code{asorti}
function, which was introduced in version 3.1.2 of @code{gawk}.
As of release time, @code{gawk} version 4.2.0 is the newest verified
to work to build @theglibc{}.

@item
GNU @code{bison} 2.7 or later

@code{bison} is used to generate the @code{yacc} parser code in the @file{intl}
subdirectory.  As of release time, @code{bison} version 3.0.4 is the newest
verified to work to build @theglibc{}.

@item
Perl 5

Perl is not required, but it is used if present to test the
installation.  We may decide to use it elsewhere in the future.

@item
GNU @code{sed} 3.02 or newer

@code{Sed} is used in several places to generate files.  Most scripts work
with any version of @code{sed}.  As of release time, @code{sed} version
4.4 is the newest verified to work to build @theglibc{}.

@end itemize

@noindent
If you change any of the @file{configure.ac} files you will also need

@itemize @bullet
@item
GNU @code{autoconf} 2.69 (exactly)
@end itemize

@noindent
and if you change any of the message translation files you will need

@itemize @bullet
@item
GNU @code{gettext} 0.10.36 or later
@end itemize


@noindent
You may also need these packages if you upgrade your source tree using
patches, although we try to avoid this.

@node Linux
@appendixsec Specific advice for @gnulinuxsystems{}
@cindex kernel header files

If you are installing @theglibc{} on @gnulinuxsystems{}, you need to have
the header files from a 3.2 or newer kernel around for reference.
(For the ia64 architecture, you need version 3.2.18 or newer because this
is the first version with support for the @code{accept4} system call.)
These headers must be installed using @samp{make headers_install}; the
headers present in the kernel source directory are not suitable for
direct use by @theglibc{}.  You do not need to use that kernel, just have
its headers installed where @theglibc{} can access them, referred to here as
@var{install-directory}.  The easiest way to do this is to unpack it
in a directory such as @file{/usr/src/linux-@var{version}}.  In that
directory, run @samp{make headers_install
INSTALL_HDR_PATH=@var{install-directory}}.  Finally, configure @theglibc{}
with the option @samp{--with-headers=@var{install-directory}/include}.
Use the most recent kernel you can get your hands on.  (If you are
cross-compiling @theglibc{}, you need to specify
@samp{ARCH=@var{architecture}} in the @samp{make headers_install}
command, where @var{architecture} is the architecture name used by the
Linux kernel, such as @samp{x86} or @samp{powerpc}.)

After installing @theglibc{}, you may need to remove or rename
directories such as @file{/usr/include/linux} and
@file{/usr/include/asm}, and replace them with copies of directories
such as @file{linux} and @file{asm} from
@file{@var{install-directory}/include}.  All directories present in
@file{@var{install-directory}/include} should be copied, except that
@theglibc{} provides its own version of @file{/usr/include/scsi}; the
files provided by the kernel should be copied without replacing those
provided by @theglibc{}.  The @file{linux}, @file{asm} and
@file{asm-generic} directories are required to compile programs using
@theglibc{}; the other directories describe interfaces to the kernel but
are not required if not compiling programs using those interfaces.
You do not need to copy kernel headers if you did not specify an
alternate kernel header source using @samp{--with-headers}.

The Filesystem Hierarchy Standard for @gnulinuxsystems{} expects some
components of the @glibcadj{} installation to be in
@file{/lib} and some in @file{/usr/lib}.  This is handled automatically
if you configure @theglibc{} with @samp{--prefix=/usr}.  If you set some other
prefix or allow it to default to @file{/usr/local}, then all the
components are installed there.

@node Reporting Bugs
@appendixsec Reporting Bugs
@cindex reporting bugs
@cindex bugs, reporting

There are probably bugs in @theglibc{}.  There are certainly
errors and omissions in this manual.  If you report them, they will get
fixed.  If you don't, no one will ever know about them and they will
remain unfixed for all eternity, if not longer.

It is a good idea to verify that the problem has not already been
reported.  Bugs are documented in two places: The file @file{BUGS}
describes a number of well known bugs and the central @glibcadj{}
bug tracking system has a
WWW interface at
@url{https://sourceware.org/bugzilla/}.  The WWW
interface gives you access to open and closed reports.  A closed report
normally includes a patch or a hint on solving the problem.

To report a bug, first you must find it.  With any luck, this will be the
hard part.  Once you've found a bug, make sure it's really a bug.  A
good way to do this is to see if @theglibc{} behaves the same way
some other C library does.  If so, probably you are wrong and the
libraries are right (but not necessarily).  If not, one of the libraries
is probably wrong.  It might not be @theglibc{}.  Many historical
Unix C libraries permit things that we don't, such as closing a file
twice.

If you think you have found some way in which @theglibc{} does not
conform to the ISO and POSIX standards (@pxref{Standards and
Portability}), that is definitely a bug.  Report it!

Once you're sure you've found a bug, try to narrow it down to the
smallest test case that reproduces the problem.  In the case of a C
library, you really only need to narrow it down to one library
function call, if possible.  This should not be too difficult.

The final step when you have a simple test case is to report the bug.
Do this at @value{REPORT_BUGS_TO}.

If you are not sure how a function should behave, and this manual
doesn't tell you, that's a bug in the manual.  Report that too!  If the
function's behavior disagrees with the manual, then either the library
or the manual has a bug, so report the disagreement.  If you find any
errors or omissions in this manual, please report them to the
bug database.  If you refer to specific
sections of the manual, please include the section names for easier
identification.