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| <h4 class="appendixsubsec">D.2.1 Layout of the <samp><span class="file">sysdeps</span></samp> Directory Hierarchy</h4> |
| |
| <p>A GNU configuration name has three parts: the CPU type, the |
| manufacturer's name, and the operating system. <samp><span class="file">configure</span></samp> uses |
| these to pick the list of system-dependent directories to look for. If |
| the ‘<samp><span class="samp">--nfp</span></samp>’ option is <em>not</em> passed to <samp><span class="file">configure</span></samp>, the |
| directory <samp><var>machine</var><span class="file">/fpu</span></samp> is also used. The operating system |
| often has a <dfn>base operating system</dfn>; for example, if the operating |
| system is ‘<samp><span class="samp">Linux</span></samp>’, the base operating system is ‘<samp><span class="samp">unix/sysv</span></samp>’. |
| The algorithm used to pick the list of directories is simple: |
| <samp><span class="file">configure</span></samp> 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 ‘<samp><span class="samp">i686-linux-gnu</span></samp>’<!-- /@w --> |
| results in <samp><span class="file">unix/sysv/linux/i386/i686</span></samp>. <samp><span class="file">configure</span></samp> then |
| tries removing each element of the list in turn, so |
| <samp><span class="file">unix/sysv/linux</span></samp> and <samp><span class="file">unix/sysv</span></samp> 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 <samp><span class="file">irix6.2</span></samp> and <samp><span class="file">irix6.3</span></samp> directories, |
| <samp><span class="file">configure</span></samp> tries successively less specific operating system names |
| by removing trailing suffixes starting with a period. |
| |
| <p>As an example, here is the complete list of directories that would be |
| tried for the configuration ‘<samp><span class="samp">i686-linux-gnu</span></samp>’<!-- /@w --> (with the |
| <samp><span class="file">crypt</span></samp> and <samp><span class="file">linuxthreads</span></samp> add-on): |
| |
| <pre class="smallexample"> 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 |
| </pre> |
| <p>Different machine architectures are conventionally subdirectories at the |
| top level of the <samp><span class="file">sysdeps</span></samp> directory tree. For example, |
| <samp><span class="file">sysdeps/sparc</span></samp><!-- /@w --> and <samp><span class="file">sysdeps/m68k</span></samp><!-- /@w -->. 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 |
| <samp><span class="file">sysdeps/m68k/68020</span></samp><!-- /@w -->. Code which is specific to the |
| floating-point coprocessor used with a particular machine should go in |
| <samp><span class="file">sysdeps/</span><var>machine</var><span class="file">/fpu</span></samp><!-- /@w -->. |
| |
| <p>There are a few directories at the top level of the <samp><span class="file">sysdeps</span></samp> |
| hierarchy that are not for particular machine architectures. |
| |
| <dl> |
| <dt><samp><span class="file">generic</span></samp><dd>As described above (see <a href="Porting.html#Porting">Porting</a>), this is the subdirectory |
| that every configuration implicitly uses after all others. |
| |
| <br><dt><samp><span class="file">ieee754</span></samp><dd>This directory is for code using the IEEE 754 floating-point format, |
| where the C type <code>float</code> is IEEE 754 single-precision format, and |
| <code>double</code> is IEEE 754 double-precision format. Usually this |
| directory is referred to in the <samp><span class="file">Implies</span></samp> file in a machine |
| architecture-specific directory, such as <samp><span class="file">m68k/Implies</span></samp>. |
| |
| <br><dt><samp><span class="file">libm-ieee754</span></samp><dd>This directory contains an implementation of a mathematical library |
| usable on platforms which use IEEE 754<!-- /@w --> conformant floating-point |
| arithmetic. |
| |
| <br><dt><samp><span class="file">libm-i387</span></samp><dd>This is a special case. Ideally the code should be in |
| <samp><span class="file">sysdeps/i386/fpu</span></samp> but for various reasons it is kept aside. |
| |
| <br><dt><samp><span class="file">posix</span></samp><dd>This directory contains implementations of things in the library in |
| terms of <span class="sc">POSIX.1</span> functions. This includes some of the <span class="sc">POSIX.1</span> |
| functions themselves. Of course, <span class="sc">POSIX.1</span> cannot be completely |
| implemented in terms of itself, so a configuration using just |
| <samp><span class="file">posix</span></samp> cannot be complete. |
| |
| <br><dt><samp><span class="file">unix</span></samp><dd>This is the directory for Unix-like things. See <a href="Porting-to-Unix.html#Porting-to-Unix">Porting to Unix</a>. |
| <samp><span class="file">unix</span></samp> implies <samp><span class="file">posix</span></samp>. There are some special-purpose |
| subdirectories of <samp><span class="file">unix</span></samp>: |
| |
| <dl> |
| <dt><samp><span class="file">unix/common</span></samp><dd>This directory is for things common to both BSD and System V release 4. |
| Both <samp><span class="file">unix/bsd</span></samp> and <samp><span class="file">unix/sysv/sysv4</span></samp> imply <samp><span class="file">unix/common</span></samp>. |
| |
| <br><dt><samp><span class="file">unix/inet</span></samp><dd>This directory is for <code>socket</code> and related functions on Unix systems. |
| <samp><span class="file">unix/inet/Subdirs</span></samp> enables the <samp><span class="file">inet</span></samp> top-level subdirectory. |
| <samp><span class="file">unix/common</span></samp> implies <samp><span class="file">unix/inet</span></samp>. |
| </dl> |
| |
| <br><dt><samp><span class="file">mach</span></samp><dd>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 <samp><span class="file">sysdeps</span></samp> hierarchy, parallel to <samp><span class="file">unix</span></samp> and <samp><span class="file">mach</span></samp>. |
| </dl> |
| |
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