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   2   Copyright 1988-2022 Free Software Foundation, Inc.
   3   This is part of the GCC manual.
   4   For copying conditions, see the copyright.rst file.
   5
   6 .. _arc-function-attributes:
   7
   8 ARC Function Attributes
   9 ^^^^^^^^^^^^^^^^^^^^^^^
  10
  11 These function attributes are supported by the ARC back end:
  12
  13 .. index:: interrupt function attribute, ARC
  14
  15 .. arc-fn-attr:: interrupt
  16
  17   Use this attribute to indicate
  18   that the specified function is an interrupt handler.  The compiler generates
  19   function entry and exit sequences suitable for use in an interrupt handler
  20   when this attribute is present.
  21
  22   On the ARC, you must specify the kind of interrupt to be handled
  23   in a parameter to the interrupt attribute like this:
  24
  25   .. code-block:: c++
  26
  27     void f () __attribute__ ((interrupt ("ilink1")));
  28
  29   Permissible values for this parameter are: ``ilink1`` and
  30   ``ilink2`` for ARCv1 architecture, and ``ilink`` and
  31   ``firq`` for ARCv2 architecture.
  32
  33 .. index:: long_call function attribute, ARC, medium_call function attribute, ARC, short_call function attribute, ARC, indirect calls, ARC
  34
  35 .. arc-fn-attr:: long_call, medium_call, short_call
  36
  37   These attributes specify how a particular function is called.
  38   These attributes override the
  39   :option:`-mlong-calls` and :option:`-mmedium-calls` (see :ref:`arc-options`)
  40   command-line switches and ``#pragma long_calls`` settings.
  41
  42   For ARC, a function marked with the :arc-fn-attr:`long_call` attribute is
  43   always called using register-indirect jump-and-link instructions,
  44   thereby enabling the called function to be placed anywhere within the
  45   32-bit address space.  A function marked with the ``medium_call``
  46   attribute will always be close enough to be called with an unconditional
  47   branch-and-link instruction, which has a 25-bit offset from
  48   the call site.  A function marked with the ``short_call``
  49   attribute will always be close enough to be called with a conditional
  50   branch-and-link instruction, which has a 21-bit offset from
  51   the call site.
  52
  53 .. index:: jli_always function attribute, ARC
  54
  55 .. arc-fn-attr:: jli_always
  56
  57   Forces a particular function to be called using ``jli``
  58   instruction.  The ``jli`` instruction makes use of a table stored
  59   into ``.jlitab`` section, which holds the location of the functions
  60   which are addressed using this instruction.
  61
  62 .. index:: jli_fixed function attribute, ARC
  63
  64 .. arc-fn-attr:: jli_fixed
  65
  66   Identical like the above one, but the location of the function in the
  67   ``jli`` table is known and given as an attribute parameter.
  68
  69 .. index:: secure_call function attribute, ARC
  70
  71 .. arc-fn-attr:: secure_call
  72
  73   This attribute allows one to mark secure-code functions that are
  74   callable from normal mode.  The location of the secure call function
  75   into the ``sjli`` table needs to be passed as argument.
  76
  77 .. index:: naked function attribute, ARC
  78
  79 .. arc-fn-attr:: naked
  80
  81   This attribute allows the compiler to construct the requisite function
  82   declaration, while allowing the body of the function to be assembly
  83   code.  The specified function will not have prologue/epilogue
  84   sequences generated by the compiler.  Only basic ``asm`` statements
  85   can safely be included in naked functions (see :ref:`basic-asm`).  While
  86   using extended ``asm`` or a mixture of basic ``asm`` and C code
  87   may appear to work, they cannot be depended upon to work reliably and
  88   are not supported.