..
  Copyright 1988-2022 Free Software Foundation, Inc.
  This is part of the GCC manual.
  For copying conditions, see the copyright.rst file.

.. index:: target hooks, target functions

.. _target-structure:

The Global targetm Variable
***************************

.. index:: targetm

Variable struct gcc_target targetmThe target :samp:`.c` file must define the global ``targetm`` variable
which contains pointers to functions and data relating to the target
machine.  The variable is declared in :samp:`target.h`;
:samp:`target-def.h` defines the macro ``TARGET_INITIALIZER`` which is
used to initialize the variable, and macros for the default initializers
for elements of the structure.  The :samp:`.c` file should override those
macros for which the default definition is inappropriate.  For example:

.. code-block:: c++

  #include "target.h"
  #include "target-def.h"

  /* Initialize the GCC target structure.  */

  #undef TARGET_COMP_TYPE_ATTRIBUTES
  #define TARGET_COMP_TYPE_ATTRIBUTES machine_comp_type_attributes

  struct gcc_target targetm = TARGET_INITIALIZER;

Where a macro should be defined in the :samp:`.c` file in this manner to
form part of the ``targetm`` structure, it is documented below as a
'Target Hook' with a prototype.  Many macros will change in future
from being defined in the :samp:`.h` file to being part of the
``targetm`` structure.

Similarly, there is a ``targetcm`` variable for hooks that are
specific to front ends for C-family languages, documented as 'C
Target Hook'.  This is declared in :samp:`c-family/c-target.h`, the
initializer ``TARGETCM_INITIALIZER`` in
:samp:`c-family/c-target-def.h`.  If targets initialize ``targetcm``
themselves, they should set ``target_has_targetcm=yes`` in
:samp:`config.gcc`; otherwise a default definition is used.

Similarly, there is a ``targetm_common`` variable for hooks that
are shared between the compiler driver and the compilers proper,
documented as 'Common Target Hook'.  This is declared in
:samp:`common/common-target.h`, the initializer
``TARGETM_COMMON_INITIALIZER`` in
:samp:`common/common-target-def.h`.  If targets initialize
``targetm_common`` themselves, they should set
``target_has_targetm_common=yes`` in :samp:`config.gcc`; otherwise a
default definition is used.

Similarly, there is a ``targetdm`` variable for hooks that are
specific to the D language front end, documented as 'D Target Hook'.
This is declared in :samp:`d/d-target.h`, the initializer
``TARGETDM_INITIALIZER`` in :samp:`d/d-target-def.h`.  If targets
initialize ``targetdm`` themselves, they should set
``target_has_targetdm=yes`` in :samp:`config.gcc`; otherwise a default
definition is used.