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):
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
There are a few directories at the top level of the sysdeps
hierarchy that are not for particular machine architectures.
As described above (see Porting), this is the subdirectory
that every configuration implicitly uses after all others.
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.
This directory contains an implementation of a mathematical library
usable on platforms which use IEEE 754 conformant floating-point
This is a special case. Ideally the code should be in
sysdeps/i386/fpu but for various reasons it is kept aside.
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.
This is the directory for Unix-like things. See Porting to Unix.
unix implies posix. There are some special-purpose
subdirectories of unix:
This directory is for things common to both BSD and System V release 4.
Both unix/bsd and unix/sysv/sysv4 imply unix/common.
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.
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.
Published under the terms of the GNU General Public License