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@c Copyright (C) 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999,

@c 2000, 2001, 2002, 2003, 2004, 2005, 2008, 2009

@c Free Software Foundation, Inc.

@c This is part of the GCC manual.

@c For copying conditions, see the file gccint.texi.

@node Host Config

@chapter Host Configuration

@cindex host configuration

Most details about the machine and system on which the compiler is

actually running are detected by the @command{configure} script.  Some

things are impossible for @command{configure} to detect; these are

described in two ways, either by macros defined in a file named

@file{xm-@var{machine}.h} or by hook functions in the file specified

by the @var{out_host_hook_obj} variable in @file{config.gcc}.  (The

intention is that very few hosts will need a header file but nearly

every fully supported host will need to override some hooks.)

If you need to define only a few 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}.

@menu

* Host Common::         Things every host probably needs implemented.

* Filesystem::          Your host can't have the letter `a' in filenames?

* Host Misc::           Rare configuration options for hosts.

@end menu

@node Host Common

@section Host Common

@cindex host hooks

@cindex host functions

Some things are just not portable, even between similar operating systems,

and are too difficult for autoconf to detect.  They get implemented using

hook functions in the file specified by the @var{host_hook_obj}

variable in @file{config.gcc}.

@deftypefn {Host Hook} void HOST_HOOKS_EXTRA_SIGNALS (void)

This host hook is used to set up handling for extra signals.  The most

common thing to do in this hook is to detect stack overflow.

@end deftypefn

@deftypefn {Host Hook} void * HOST_HOOKS_GT_PCH_GET_ADDRESS (size_t @var{size}, int @var{fd})

This host hook returns the address of some space that is likely to be

free in some subsequent invocation of the compiler.  We intend to load

the PCH data at this address such that the data need not be relocated.

The area should be able to hold @var{size} bytes.  If the host uses

@code{mmap}, @var{fd} is an open file descriptor that can be used for

probing.

@end deftypefn

@deftypefn {Host Hook} int HOST_HOOKS_GT_PCH_USE_ADDRESS (void * @var{address}, size_t @var{size}, int @var{fd}, size_t @var{offset})

This host hook is called when a PCH file is about to be loaded.

We want to load @var{size} bytes from @var{fd} at @var{offset}

into memory at @var{address}.  The given address will be the result of

a previous invocation of @code{HOST_HOOKS_GT_PCH_GET_ADDRESS}.

Return @minus{}1 if we couldn't allocate @var{size} bytes at @var{address}.

Return 0 if the memory is allocated but the data is not loaded.  Return 1

if the hook has performed everything.

If the implementation uses reserved address space, free any reserved

space beyond @var{size}, regardless of the return value.  If no PCH will

be loaded, this hook may be called with @var{size} zero, in which case

all reserved address space should be freed.

Do not try to handle values of @var{address} that could not have been

returned by this executable; just return @minus{}1.  Such values usually

indicate an out-of-date PCH file (built by some other GCC executable),

and such a PCH file won't work.

@end deftypefn

@deftypefn {Host Hook} size_t HOST_HOOKS_GT_PCH_ALLOC_GRANULARITY (void);

This host hook returns the alignment required for allocating virtual

memory.  Usually this is the same as getpagesize, but on some hosts the

alignment for reserving memory differs from the pagesize for committing

memory.

@end deftypefn

@node Filesystem

@section Host Filesystem

@cindex configuration file

@cindex @file{xm-@var{machine}.h}

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 @file{xm-@var{machine}.h}.

@ftable @code

@item HAVE_DOS_BASED_FILE_SYSTEM

This macro is automatically defined by @file{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 (@samp{/}

and @samp{\}) are directory separators.

@item DIR_SEPARATOR

@itemx DIR_SEPARATOR_2

If defined, these macros expand to character constants specifying

separators for directory names within a file specification.

@file{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 @file{xm-@var{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.

@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, but not

always, use semicolon (@samp{;}).

@item VMS

Define this macro if the host system is VMS@.

@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 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 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.

@item HOST_LACKS_INODE_NUMBERS

Define this macro if the host filesystem does not report meaningful inode

numbers in struct stat.

@end ftable

@node Host Misc

@section Host Misc

@cindex configuration file

@cindex @file{xm-@var{machine}.h}

@ftable @code

@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 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 HOST_LONG_LONG_FORMAT

If defined, the string used to indicate an argument of type @code{long

long} to functions like @code{printf}.  The default value is

@code{"ll"}.

@item HOST_LONG_FORMAT

If defined, the string used to indicate an argument of type @code{long}

to functions like @code{printf}.  The default value is @code{"l"}.

@item HOST_PTR_PRINTF

If defined, the string used to indicate an argument of type @code{void *}

to functions like @code{printf}.  The default value is @code{"%p"}.

@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}.