### 16.2 Host Filesystem

GCC needs to know a number of things about the semantics of the host machine's filesystem. Filesystems with Unix and MS-DOS semantics are automatically detected. For other systems, you can define the following macros in `xm-machine.h`.

`HAVE_DOS_BASED_FILE_SYSTEM`
  This macro is automatically defined by `system.h` if the host file system obeys the semantics defined by MS-DOS instead of Unix. DOS file systems are case insensitive, file specifications may begin with a drive letter, and both forward slash and backslash (‘`/`’ and ‘`\`’) are directory separators.
`DIR_SEPARATOR`
`DIR_SEPARATOR_2`
  If defined, these macros expand to character constants specifying separators for directory names within a file specification. `system.h` will automatically give them appropriate values on Unix and MS-DOS file systems. If your file system is neither of these, define one or both appropriately in `xm-machine.h`.

  However, operating systems like VMS, where constructing a pathname is more complicated than just stringing together directory names separated by a special character, should not define either of these macros.

`PATH_SEPARATOR`
  If defined, this macro should expand to a character constant specifying the separator for elements of search paths. The default value is a colon (‘`:`’). DOS-based systems usually, but not always, use semicolon (‘`;`’).
`VMS`
  Define this macro if the host system is VMS.
`HOST_OBJECT_SUFFIX`
  Define this macro to be a C string representing the suffix for object files on your host machine. If you do not define this macro, GCC will use ‘`.o`’ as the suffix for object files.
`HOST_EXECUTABLE_SUFFIX`
  Define this macro to be a C string representing the suffix for executable files on your host machine. If you do not define this macro, GCC will use the null string as the suffix for executable files.
`HOST_BIT_BUCKET`
  A pathname defined by the host operating system, which can be opened as a file and written to, but all the information written is discarded. This is commonly known as a bit bucket or null device. If you do not define this macro, GCC will use ‘`/dev/null`’ as the bit bucket. If the host does not support a bit bucket, define this macro to an invalid filename.
`UPDATE_PATH_HOST_CANONICALIZE (`path`)`
  If defined, a C statement (sans semicolon) that performs host-dependent canonicalization when a path used in a compilation driver or preprocessor is canonicalized. path is a malloc-ed path to be canonicalized. If the C statement does canonicalize path into a different buffer, the old path should be freed and the new buffer should have been allocated with malloc.
`DUMPFILE_FORMAT`
  Define this macro to be a C string representing the format to use for constructing the index part of debugging dump file names. The resultant string must fit in fifteen bytes. The full filename will be the concatenation of: the prefix of the assembler file name, the string resulting from applying this format to an index number, and a string unique to each dump file kind, e.g. ‘`rtl`’.

  If you do not define this macro, GCC will use ‘`.%02d.`’. You should define this macro if using the default will create an invalid file name.

`DELETE_IF_ORDINARY`
  Define this macro to be a C statement (sans semicolon) that performs host-dependent removal of ordinary temp files in the compilation driver.

  If you do not define this macro, GCC will use the default version. You should define this macro if the default version does not reliably remove the temp file as, for example, on VMS which allows multiple versions of a file.

`HOST_LACKS_INODE_NUMBERS`
  Define this macro if the host filesystem does not report meaningful inode numbers in struct stat.