GNU Info

(libc.info)Hierarchy Conventions

---

Next: Porting to Unix Up: Porting

---

Enter node , (file) or (file)node

Layout of the `sysdeps' Directory Hierarchy
-------------------------------------------

   A GNU configuration name has three parts: the CPU type, the
manufacturer's name, and the operating system.  `configure' uses these
to pick the list of system-dependent directories to look for.  If the
`--nfp' option is _not_ passed to `configure', the directory
`MACHINE/fpu' is also used.  The operating system often has a "base
operating system"; for example, if the operating system is `Linux', the
base operating system is `unix/sysv'.  The algorithm used to pick the
list of directories is simple: `configure' makes a list of the base
operating system, manufacturer, CPU type, and operating system, in that
order.  It then concatenates all these together with slashes in
between, to produce a directory name; for example, the configuration
`i686-linux-gnu' results in `unix/sysv/linux/i386/i686'.  `configure'
then tries removing each element of the list in turn, so
`unix/sysv/linux' and `unix/sysv' are also tried, among others.  Since
the precise version number of the operating system is often not
important, and it would be very inconvenient, for example, to have
identical `irix6.2' and `irix6.3' directories, `configure' tries
successively less specific operating system names by removing trailing
suffixes starting with a period.

   As an example, here is the complete list of directories that would be
tried for the configuration `i686-linux-gnu' (with the `crypt' and
`linuxthreads' add-on):

     sysdeps/i386/elf
     crypt/sysdeps/unix
     linuxthreads/sysdeps/unix/sysv/linux
     linuxthreads/sysdeps/pthread
     linuxthreads/sysdeps/unix/sysv
     linuxthreads/sysdeps/unix
     linuxthreads/sysdeps/i386/i686
     linuxthreads/sysdeps/i386
     linuxthreads/sysdeps/pthread/no-cmpxchg
     sysdeps/unix/sysv/linux/i386
     sysdeps/unix/sysv/linux
     sysdeps/gnu
     sysdeps/unix/common
     sysdeps/unix/mman
     sysdeps/unix/inet
     sysdeps/unix/sysv/i386/i686
     sysdeps/unix/sysv/i386
     sysdeps/unix/sysv
     sysdeps/unix/i386
     sysdeps/unix
     sysdeps/posix
     sysdeps/i386/i686
     sysdeps/i386/i486
     sysdeps/libm-i387/i686
     sysdeps/i386/fpu
     sysdeps/libm-i387
     sysdeps/i386
     sysdeps/wordsize-32
     sysdeps/ieee754
     sysdeps/libm-ieee754
     sysdeps/generic

   Different machine architectures are conventionally subdirectories at
the top level of the `sysdeps' directory tree.  For example,
`sysdeps/sparc' and `sysdeps/m68k'.  These contain files specific to
those machine architectures, but not specific to any particular
operating system.  There might be subdirectories for specializations of
those architectures, such as `sysdeps/m68k/68020'. Code which is
specific to the floating-point coprocessor used with a particular
machine should go in `sysdeps/MACHINE/fpu'.

   There are a few directories at the top level of the `sysdeps'
hierarchy that are not for particular machine architectures.

`generic'
     As described above (Note: Porting), this is the subdirectory
     that every configuration implicitly uses after all others.

`ieee754'
     This directory is for code using the IEEE 754 floating-point
     format, where the C type `float' is IEEE 754 single-precision
     format, and `double' is IEEE 754 double-precision format.  Usually
     this directory is referred to in the `Implies' file in a machine
     architecture-specific directory, such as `m68k/Implies'.

`libm-ieee754'
     This directory contains an implementation of a mathematical library
     usable on platforms which use IEEE 754 conformant floating-point
     arithmetic.

`libm-i387'
     This is a special case.  Ideally the code should be in
     `sysdeps/i386/fpu' but for various reasons it is kept aside.

`posix'
     This directory contains implementations of things in the library in
     terms of POSIX.1 functions.  This includes some of the POSIX.1
     functions themselves.  Of course, POSIX.1 cannot be completely
     implemented in terms of itself, so a configuration using just
     `posix' cannot be complete.

`unix'
     This is the directory for Unix-like things.  Note: Porting to
     Unix.  `unix' implies `posix'.  There are some special-purpose
     subdirectories of `unix':

    `unix/common'
          This directory is for things common to both BSD and System V
          release 4.  Both `unix/bsd' and `unix/sysv/sysv4' imply
          `unix/common'.

    `unix/inet'
          This directory is for `socket' and related functions on Unix
          systems.  `unix/inet/Subdirs' enables the `inet' top-level
          subdirectory.  `unix/common' implies `unix/inet'.

`mach'
     This is the directory for things based on the Mach microkernel
     from CMU (including the GNU operating system).  Other basic
     operating systems (VMS, for example) would have their own
     directories at the top level of the `sysdeps' hierarchy, parallel
     to `unix' and `mach'.