path: root/INSTALL

Installing the GNU C Library
****************************

Before you do anything else, you should read the FAQ at
<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.  *Note Tools for Compilation::,
below.

Configuring and compiling the GNU C Library
===========================================

The GNU C Library cannot be compiled in the source directory.  You must
build it in a separate build directory.  For example, if you have
unpacked the GNU C Library sources in '/src/gnu/glibc-VERSION', create a
directory '/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 'configure' located
at the top level of the source tree.  In the scenario above, you'd type

     $ ../glibc-VERSION/configure ARGS...

   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.

'configure' takes many options, but the only one that is usually
mandatory is '--prefix'.  This option tells 'configure' where you want
the GNU C Library installed.  This defaults to '/usr/local', but the
normal setting to install as the standard system library is
'--prefix=/usr' for GNU/Linux systems and '--prefix=' (an empty prefix)
for GNU/Hurd systems.

   It may also be useful to pass 'CC=COMPILER' and 'CFLAGS=FLAGS'
arguments to 'configure'.  'CC' selects the C compiler that will be
used, and '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 'CC'.  Options that may be overridden by the GNU C Library
build system for particular files, such as for optimization and
debugging, should go in 'CFLAGS'.  The default value of 'CFLAGS' is '-g
-O2', and the GNU C Library cannot be compiled without optimization, so
if 'CFLAGS' is specified it must enable optimization.  For example:

     $ ../glibc-VERSION/configure CC="gcc -m32" CFLAGS="-O3"

   To test the GNU C Library with a different set of C and C++
compilers, 'TEST_CC=COMPILER' and 'TEST_CXX=COMPILER' arguments can be
passed to 'configure'.  For example:

     $ ../glibc-VERSION/configure TEST_CC="gcc-6.4.1" TEST_CXX="g++-6.4.1"

   The following list describes all of the available options for
'configure':

'--prefix=DIRECTORY'
     Install machine-independent data files in subdirectories of
     'DIRECTORY'.  The default is to install in '/usr/local'.

'--exec-prefix=DIRECTORY'
     Install the library and other machine-dependent files in
     subdirectories of 'DIRECTORY'.  The default is to the '--prefix'
     directory if that option is specified, or '/usr/local' otherwise.

'--with-headers=DIRECTORY'
     Look for kernel header files in DIRECTORY, not '/usr/include'.  The
     GNU C Library needs information from the kernel's header files
     describing the interface to the kernel.  The GNU C Library will
     normally look in '/usr/include' for them, but if you specify this
     option, it will look in DIRECTORY instead.

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

'--enable-kernel=VERSION'
     This option is currently only useful on GNU/Linux systems.  The
     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 VERSION number is, the less
     compatibility code is added, and the faster the code gets.

'--with-binutils=DIRECTORY'
     Use the binutils (assembler and linker) in '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 the GNU C Library.  In that case, '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.

'--with-nonshared-cflags=CFLAGS'
     Use additional compiler flags CFLAGS to build the parts of the
     library which are always statically linked into applications and
     libraries even with shared linking (that is, the object files
     contained in 'lib*_nonshared.a' libraries).  The build process will
     automatically use the appropriate flags, but this option can be
     used to set additional flags required for building applications and
     libraries, to match local policy.  For example, if such a policy
     requires that all code linked into applications must be built with
     source fortification,
     '--with-nonshared-cflags=-Wp,-D_FORTIFY_SOURCE=2' will make sure
     that the objects in 'libc_nonshared.a' are compiled with this flag
     (although this will not affect the generated code in this
     particular case and potentially change debugging information and
     metadata only).

'--with-rtld-early-cflags=CFLAGS'
     Use additional compiler flags CFLAGS to build the early startup
     code of the dynamic linker.  These flags can be used to enable
     early dynamic linker diagnostics to run on CPUs which are not
     compatible with the rest of the GNU C Library, for example, due to
     compiler flags which target a later instruction set architecture
     (ISA).

'--with-timeoutfactor=NUM'
     Specify an integer NUM to scale the timeout of test programs.  This
     factor can be changed at run time using 'TIMEOUTFACTOR' environment
     variable.

'--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.

'--disable-default-pie'
     Don't build glibc programs and the testsuite as position
     independent executables (PIE). By default, glibc programs and tests
     are created as position independent executables on targets that
     support it.  If the toolchain and architecture support it, static
     executables are built as static PIE and the resulting glibc can be
     used with the GCC option, -static-pie, which is available with GCC
     8 or above, to create static PIE.

'--enable-cet'
'--enable-cet=permissive'
     Enable Intel Control-flow Enforcement Technology (CET) support.
     When the GNU C Library is built with '--enable-cet' or
     '--enable-cet=permissive', the resulting library is protected with
     indirect branch tracking (IBT) and shadow stack (SHSTK).  When CET
     is enabled, the GNU C Library is compatible with all existing
     executables and shared libraries.  This feature is currently
     supported on x86_64 and x32 with GCC 8 and binutils 2.29 or later.
     With '--enable-cet', it is an error to dlopen a non CET enabled
     shared library in CET enabled application.  With
     '--enable-cet=permissive', CET is disabled when dlopening a non CET
     enabled shared library in CET enabled application.

     NOTE: '--enable-cet' is only supported on x86_64 and x32.

'--enable-memory-tagging'
     Enable memory tagging support if the architecture supports it.
     When the GNU C Library is built with this option then the resulting
     library will be able to control the use of tagged memory when
     hardware support is present by use of the tunable
     'glibc.mem.tagging'.  This includes the generation of tagged memory
     when using the 'malloc' APIs.

     At present only AArch64 platforms with MTE provide this
     functionality, although the library will still operate (without
     memory tagging) on older versions of the architecture.

     The default is to disable support for memory tagging.

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

'--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.

'--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.

'--disable-timezone-tools'
     By default, time zone related utilities ('zic', 'zdump', and
     'tzselect') are installed with the GNU C Library.  If you are
     building these independently (e.g.  by using the '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 the GNU C Library expects as the data
     formats may change over time.  Consult the 'timezone' subdirectory
     for more details.

'--enable-stack-protector'
'--enable-stack-protector=strong'
'--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 '-fstack-protector',
     '-fstack-protector-strong' or '-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.

'--enable-bind-now'
     Disable lazy binding for installed shared objects and programs.
     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.

'--enable-pt_chown'
     The file 'pt_chown' is a helper binary for 'grantpt' (*note
     Pseudo-Terminals: Allocation.) that is installed setuid root to fix
     up pseudo-terminal ownership on GNU/Hurd.  It is not required on
     GNU/Linux, and the GNU C Library will not use the installed
     'pt_chown' program when configured with '--enable-pt_chown'.

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

'--disable-mathvec'
     By default for x86_64, the GNU C Library is built with the vector
     math library.  Use this option to disable the vector math library.

'--disable-static-c++-tests'
     By default, if the C++ toolchain lacks support for static linking,
     configure fails to find the C++ header files and the glibc build
     fails.  '--disable-static-c++-link-check' allows the glibc build to
     finish, but static C++ tests will fail if the C++ toolchain doesn't
     have the necessary static C++ libraries.  Use this option to skip
     the static C++ tests.  This option implies
     '--disable-static-c++-link-check'.

'--disable-static-c++-link-check'
     By default, if the C++ toolchain lacks support for static linking,
     configure fails to find the C++ header files and the glibc build
     fails.  Use this option to disable the static C++ link check so
     that the C++ header files can be located.  The newly built libc.a
     can be used to create static C++ tests if the C++ toolchain has the
     necessary static C++ libraries.

'--disable-scv'
     Disable using 'scv' instruction for syscalls.  All syscalls will
     use 'sc' instead, even if the kernel supports 'scv'.  PowerPC only.

'--build=BUILD-SYSTEM'
'--host=HOST-SYSTEM'
     These options are for cross-compiling.  If you specify both options
     and BUILD-SYSTEM is different from HOST-SYSTEM, 'configure' will
     prepare to cross-compile the GNU C Library from BUILD-SYSTEM to be
     used on HOST-SYSTEM.  You'll probably need the '--with-headers'
     option too, and you may have to override CONFIGURE's selection of
     the compiler and/or binutils.

     If you only specify '--host', '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 'configure' guesses your machine as 'i686-pc-linux-gnu'
     but you want to compile a library for 586es, give
     '--host=i586-pc-linux-gnu' or just '--host=i586-linux' and add the
     appropriate compiler flags ('-mcpu=i586' will do the trick) to
     'CC'.

     If you specify just '--build', 'configure' will get confused.

'--with-pkgversion=VERSION'