tm.texi

GUN开源阻止下的编译器GCC

@c Copyright (C) 1988, 1989, 1992, 1993, 1994 Free Software Foundation, Inc.
@c This is part of the GCC manual.
@c For copying conditions, see the file gcc.texi.

@node Target Macros
@chapter Target Description Macros
@cindex machine description macros
@cindex target description macros
@cindex macros, target description
@cindex @file{tm.h} macros

In addition to the file @file{@var{machine}.md}, a machine description
includes a C header file conventionally given the name
@file{@var{machine}.h}.  This header file defines numerous macros
that convey the information about the target machine that does not fit
into the scheme of the @file{.md} file.  The file @file{tm.h} should be
a link to @file{@var{machine}.h}.  The header file @file{config.h}
includes @file{tm.h} and most compiler source files include
@file{config.h}.

@menu
* Driver::              Controlling how the driver runs the compilation passes.
* Run-time Target::     Defining @samp{-m} options like @samp{-m68000} and @samp{-m68020}.
* Storage Layout::      Defining sizes and alignments of data.
* Type Layout::         Defining sizes and properties of basic user data types.
* Registers::           Naming and describing the hardware registers.
* Register Classes::    Defining the classes of hardware registers.
* Stack and Calling::   Defining which way the stack grows and by how much.
* Varargs::		Defining the varargs macros.
* Trampolines::         Code set up at run time to enter a nested function.
* Library Calls::       Controlling how library routines are implicitly called.
* Addressing Modes::    Defining addressing modes valid for memory operands.
* Condition Code::      Defining how insns update the condition code.
* Costs::               Defining relative costs of different operations.
* Sections::            Dividing storage into text, data, and other sections.
* PIC::			Macros for position independent code.
* Assembler Format::    Defining how to write insns and pseudo-ops to output.
* Debugging Info::      Defining the format of debugging output.
* Cross-compilation::   Handling floating point for cross-compilers.
* Misc::                Everything else.
@end menu

@node Driver
@section Controlling the Compilation Driver, @file{gcc}
@cindex driver
@cindex controlling the compilation driver

@c prevent bad page break with this line
You can control the compilation driver.

@table @code
@findex SWITCH_TAKES_ARG
@item SWITCH_TAKES_ARG (@var{char})
A C expression which determines whether the option @samp{-@var{char}}
takes arguments.  The value should be the number of arguments that
option takes--zero, for many options.

By default, this macro is defined to handle the standard options
properly.  You need not define it unless you wish to add additional
options which take arguments.

@findex WORD_SWITCH_TAKES_ARG
@item WORD_SWITCH_TAKES_ARG (@var{name})
A C expression which determines whether the option @samp{-@var{name}}
takes arguments.  The value should be the number of arguments that
option takes--zero, for many options.  This macro rather than
@code{SWITCH_TAKES_ARG} is used for multi-character option names.

By default, this macro is defined as
@code{DEFAULT_WORD_SWITCH_TAKES_ARG}, which handles the standard options
properly.  You need not define @code{WORD_SWITCH_TAKES_ARG} unless you
wish to add additional options which take arguments.  Any redefinition
should call @code{DEFAULT_WORD_SWITCH_TAKES_ARG} and then check for
additional options.

@findex SWITCHES_NEED_SPACES
@item SWITCHES_NEED_SPACES
A string-valued C expression which is nonempty if the linker needs a
space between the @samp{-L} or @samp{-o} option and its argument.

If this macro is not defined, the default value is 0.

@findex CPP_SPEC
@item CPP_SPEC
A C string constant that tells the GNU CC driver program options to
pass to CPP.  It can also specify how to translate options you
give to GNU CC into options for GNU CC to pass to the CPP.

Do not define this macro if it does not need to do anything.

@findex NO_BUILTIN_SIZE_TYPE
@item NO_BUILTIN_SIZE_TYPE
If this macro is defined, the preprocessor will not define the builtin macro
@code{__SIZE_TYPE__}.  The macro @code{__SIZE_TYPE__} must then be defined
by @code{CPP_SPEC} instead.

This should be defined if @code{SIZE_TYPE} depends on target dependent flags
which are not accessible to the preprocessor.  Otherwise, it should not
be defined.

@findex NO_BUILTIN_PTRDIFF_TYPE
@item NO_BUILTIN_PTRDIFF_TYPE
If this macro is defined, the preprocessor will not define the builtin macro
@code{__PTRDIFF_TYPE__}.  The macro @code{__PTRDIFF_TYPE__} must then be
defined by @code{CPP_SPEC} instead.

This should be defined if @code{PTRDIFF_TYPE} depends on target dependent flags
which are not accessible to the preprocessor.  Otherwise, it should not
be defined.

@findex SIGNED_CHAR_SPEC
@item SIGNED_CHAR_SPEC
A C string constant that tells the GNU CC driver program options to
pass to CPP.  By default, this macro is defined to pass the option
@samp{-D__CHAR_UNSIGNED__} to CPP if @code{char} will be treated as
@code{unsigned char} by @code{cc1}.

Do not define this macro unless you need to override the default
definition.

@findex CC1_SPEC
@item CC1_SPEC
A C string constant that tells the GNU CC driver program options to
pass to @code{cc1}.  It can also specify how to translate options you
give to GNU CC into options for GNU CC to pass to the @code{cc1}.

Do not define this macro if it does not need to do anything.

@findex CC1PLUS_SPEC
@item CC1PLUS_SPEC
A C string constant that tells the GNU CC driver program options to
pass to @code{cc1plus}.  It can also specify how to translate options you
give to GNU CC into options for GNU CC to pass to the @code{cc1plus}.

Do not define this macro if it does not need to do anything.

@findex ASM_SPEC
@item ASM_SPEC
A C string constant that tells the GNU CC driver program options to
pass to the assembler.  It can also specify how to translate options
you give to GNU CC into options for GNU CC to pass to the assembler.
See the file @file{sun3.h} for an example of this.

Do not define this macro if it does not need to do anything.

@findex ASM_FINAL_SPEC
@item ASM_FINAL_SPEC
A C string constant that tells the GNU CC driver program how to
run any programs which cleanup after the normal assembler.
Normally, this is not needed.  See the file @file{mips.h} for
an example of this.

Do not define this macro if it does not need to do anything.

@findex LINK_SPEC
@item LINK_SPEC
A C string constant that tells the GNU CC driver program options to
pass to the linker.  It can also specify how to translate options you
give to GNU CC into options for GNU CC to pass to the linker.

Do not define this macro if it does not need to do anything.

@findex LIB_SPEC
@item LIB_SPEC
Another C string constant used much like @code{LINK_SPEC}.  The difference
between the two is that @code{LIB_SPEC} is used at the end of the
command given to the linker.

If this macro is not defined, a default is provided that
loads the standard C library from the usual place.  See @file{gcc.c}.

@findex LIBGCC_SPEC
@item LIBGCC_SPEC
Another C string constant that tells the GNU CC driver program
how and when to place a reference to @file{libgcc.a} into the
linker command line.  This constant is placed both before and after
the value of @code{LIB_SPEC}.

If this macro is not defined, the GNU CC driver provides a default that
passes the string @samp{-lgcc} to the linker unless the @samp{-shared}
option is specified.

@findex STARTFILE_SPEC
@item STARTFILE_SPEC
Another C string constant used much like @code{LINK_SPEC}.  The
difference between the two is that @code{STARTFILE_SPEC} is used at
the very beginning of the command given to the linker.

If this macro is not defined, a default is provided that loads the
standard C startup file from the usual place.  See @file{gcc.c}.

@findex ENDFILE_SPEC
@item ENDFILE_SPEC
Another C string constant used much like @code{LINK_SPEC}.  The
difference between the two is that @code{ENDFILE_SPEC} is used at
the very end of the command given to the linker.

Do not define this macro if it does not need to do anything.

@findex LINK_LIBGCC_SPECIAL
@item LINK_LIBGCC_SPECIAL
Define this macro if the driver program should find the library
@file{libgcc.a} itself and should not pass @samp{-L} options to the
linker.  If you do not define this macro, the driver program will pass
the argument @samp{-lgcc} to tell the linker to do the search and will
pass @samp{-L} options to it.

@findex LINK_LIBGCC_SPECIAL_1
@item LINK_LIBGCC_SPECIAL_1
Define this macro if the driver program should find the library
@file{libgcc.a}.  If you do not define this macro, the driver program will pass
the argument @samp{-lgcc} to tell the linker to do the search.
This macro is similar to @code{LINK_LIBGCC_SPECIAL}, except that it does
not affect @samp{-L} options.

@findex MULTILIB_DEFAULTS
@item MULTILIB_DEFAULTS
Define this macro as a C expression for the initializer of an array of
string to tell the driver program which options are defaults for this
target and thus do not need to be handled specially when using
@code{MULTILIB_OPTIONS}. 

Do not define this macro if @code{MULTILIB_OPTIONS} is not defined in
the target makefile fragment or if none of the options listed in
@code{MULTILIB_OPTIONS} are set by default.
@xref{Target Fragment}.

@findex RELATIVE_PREFIX_NOT_LINKDIR
@item RELATIVE_PREFIX_NOT_LINKDIR
Define this macro to tell @code{gcc} that it should only translate
a @samp{-B} prefix into a @samp{-L} linker option if the prefix
indicates an absolute file name.

@findex STANDARD_EXEC_PREFIX
@item STANDARD_EXEC_PREFIX
Define this macro as a C string constant if you wish to override the
standard choice of @file{/usr/local/lib/gcc-lib/} as the default prefix to
try when searching for the executable files of the compiler.

@findex MD_EXEC_PREFIX
@item MD_EXEC_PREFIX
If defined, this macro is an additional prefix to try after
@code{STANDARD_EXEC_PREFIX}.  @code{MD_EXEC_PREFIX} is not searched
when the @samp{-b} option is used, or the compiler is built as a cross
compiler.

@findex STANDARD_STARTFILE_PREFIX
@item STANDARD_STARTFILE_PREFIX
Define this macro as a C string constant if you wish to override the
standard choice of @file{/usr/local/lib/} as the default prefix to
try when searching for startup files such as @file{crt0.o}.

@findex MD_STARTFILE_PREFIX
@item MD_STARTFILE_PREFIX
If defined, this macro supplies an additional prefix to try after the
standard prefixes.  @code{MD_EXEC_PREFIX} is not searched when the
@samp{-b} option is used, or when the compiler is built as a cross
compiler.

@findex MD_STARTFILE_PREFIX_1
@item MD_STARTFILE_PREFIX_1
If defined, this macro supplies yet another prefix to try after the
standard prefixes.  It is not searched when the @samp{-b} option is
used, or when the compiler is built as a cross compiler.

@findex INIT_ENVIRONMENT
@item INIT_ENVIRONMENT
Define this macro as a C string constant if you with to set environment
variables for programs called by the driver, such as the assembler and
loader.  The driver passes the value of this macro to @code{putenv} to
initialize the necessary environment variables.

@findex LOCAL_INCLUDE_DIR
@item LOCAL_INCLUDE_DIR
Define this macro as a C string constant if you wish to override the
standard choice of @file{/usr/local/include} as the default prefix to
try when searching for local header files.  @code{LOCAL_INCLUDE_DIR}
comes before @code{SYSTEM_INCLUDE_DIR} in the search order.

Cross compilers do not use this macro and do not search either
@file{/usr/local/include} or its replacement.

@findex SYSTEM_INCLUDE_DIR
@item SYSTEM_INCLUDE_DIR
Define this macro as a C string constant if you wish to specify a
system-specific directory to search for header files before the standard
directory.  @code{SYSTEM_INCLUDE_DIR} comes before
@code{STANDARD_INCLUDE_DIR} in the search order.

Cross compilers do not use this macro and do not search the directory
specified.

@findex STANDARD_INCLUDE_DIR
@item STANDARD_INCLUDE_DIR
Define this macro as a C string constant if you wish to override the
standard choice of @file{/usr/include} as the default prefix to
try when searching for header files.

Cross compilers do not use this macro and do not search either
@file{/usr/include} or its replacement.

@findex INCLUDE_DEFAULTS
@item INCLUDE_DEFAULTS
Define this macro if you wish to override the entire default search path
for include files.  The default search path includes
@code{GCC_INCLUDE_DIR}, @code{LOCAL_INCLUDE_DIR},
@code{SYSTEM_INCLUDE_DIR}, @code{GPLUSPLUS_INCLUDE_DIR}, and
@code{STANDARD_INCLUDE_DIR}.  In addition, @code{GPLUSPLUS_INCLUDE_DIR}
and @code{GCC_INCLUDE_DIR} are defined automatically by @file{Makefile},
and specify private search areas for GCC.  The directory
@code{GPLUSPLUS_INCLUDE_DIR} is used only for C++ programs.

The definition should be an initializer for an array of structures.
Each array element should have two elements: the directory name (a
string constant) and a flag for C++-only directories.  Mark the end of
the array with a null element.  For example, here is the definition used
for VMS:

@example
#define INCLUDE_DEFAULTS \
@{                                       \
  @{ "GNU_GXX_INCLUDE:", 1@},             \
  @{ "GNU_CC_INCLUDE:", 0@},              \
  @{ "SYS$SYSROOT:[SYSLIB.]", 0@},        \
  @{ ".", 0@},                            \
  @{ 0, 0@}                               \
@}
@end example
@end table

Here is the order of prefixes tried for exec files: