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+@c Copyright (C) 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998,
+@c 1999, 2000, 2001, 2002 Free Software Foundation, Inc.
+@c This is part of the GCC manual.
+@c For copying conditions, see the file gcc.texi.
+
+@node Host Config
+@chapter Host Configuration Headers
+@cindex configuration file
+@cindex @file{xm-@var{machine}.h}
+
+Host configuration headers contain macro definitions that describe the
+machine and system on which the compiler is running.  They are usually
+unnecessary.  Most of the things GCC needs to know about the host
+system can be deduced by the @command{configure} script.
+
+If your host does need a special configuration header, it should be
+named @file{xm-@var{machine}.h}, where @var{machine} is a short mnemonic
+for the machine.  Here are some macros which this header can define.
+
+@ftable @code
+@item VMS
+Define this macro if the host system is VMS@.
+
+@item FATAL_EXIT_CODE
+A C expression for the status code to be returned when the compiler
+exits after serious errors.  The default is the system-provided macro
+@samp{EXIT_FAILURE}, or @samp{1} if the system doesn't define that
+macro.  Define this macro only if these defaults are incorrect.
+
+@item SUCCESS_EXIT_CODE
+A C expression for the status code to be returned when the compiler
+exits without serious errors.  (Warnings are not serious errors.)  The
+default is the system-provided macro @samp{EXIT_SUCCESS}, or @samp{0} if
+the system doesn't define that macro.  Define this macro only if these
+defaults are incorrect.
+
+@item USE_C_ALLOCA
+Define this macro if GCC should use the C implementation of @code{alloca}
+provided by @file{libiberty.a}.  This only affects how some parts of the
+compiler itself allocate memory.  It does not change code generation.
+
+When GCC is built with a compiler other than itself, the C @code{alloca}
+is always used.  This is because most other implementations have serious
+bugs.  You should define this macro only on a system where no
+stack-based @code{alloca} can possibly work.  For instance, if a system
+has a small limit on the size of the stack, GCC's builtin @code{alloca}
+will not work reliably.
+
+@item HAVE_DOS_BASED_FILE_SYSTEM
+Define this macro 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 (@samp{/} and @samp{\}) are directory separators.  If you
+define this macro, you probably need to define the next three macros too.
+
+@item 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 (@samp{:}).  DOS-based systems usually use semicolon (@samp{;}).
+
+@item DIR_SEPARATOR
+@itemx DIR_SEPARATOR_2
+If defined, these macros expand to character constants specifying
+separators for directory names within a file specification.  They are
+used somewhat inconsistently throughout the compiler.  If your system
+behaves like Unix (only forward slash separates pathnames), define
+neither of them.  If your system behaves like DOS (both forward and
+backward slash can be used), define @code{DIR_SEPARATOR} to @samp{/}
+and @code{DIR_SEPARATOR_2} to @samp{\}.
+
+@item 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 @samp{.o} as the suffix for object files.
+
+@item 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.
+
+@item 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 @dfn{bit bucket} or @dfn{null device}.  If
+you do not define this macro, GCC will use @samp{/dev/null} as the bit
+bucket.  If the host does not support a bit bucket, define this macro to
+an invalid filename.
+
+@item COLLECT2_HOST_INITIALIZATION
+If defined, a C statement (sans semicolon) that performs host-dependent
+initialization when @code{collect2} is being initialized.
+
+@item GCC_DRIVER_HOST_INITIALIZATION
+If defined, a C statement (sans semicolon) that performs host-dependent
+initialization when a compilation driver is being initialized.
+
+@item UPDATE_PATH_HOST_CANONICALIZE (@var{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.  @var{path} is a malloc-ed path to be
+canonicalized.  If the C statement does canonicalize @var{path} into a
+different buffer, the old path should be freed and the new buffer should
+have been allocated with malloc.
+
+@item 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. @samp{rtl}.
+
+If you do not define this macro, GCC will use @samp{.%02d.}.  You should
+define this macro if using the default will create an invalid file name.
+
+@item SMALL_ARG_MAX
+Define this macro if the host system has a small limit on the total
+size of an argument vector.  This causes the driver to take more care
+not to pass unnecessary arguments to subprocesses.
+@end ftable
+
+In addition, if @command{configure} generates an incorrect definition of
+any of the macros in @file{auto-host.h}, you can override that
+definition in a host configuration header.  If you need to do this,
+first see if it is possible to fix @command{configure}.
+
+If you need to define only a few of these macros, and they have simple
+definitions, consider using the @code{xm_defines} variable in your
+@file{config.gcc} entry instead of creating a host configuration header.
+@xref{System Config}.