sysdeps/generic/ifunc-init.h

   1 /* IFUNC generic definitions.
   2    This file is part of the GNU C Library.
   3    Copyright (C) 2017-2018 Free Software Foundation, Inc.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, see
  17    <http://www.gnu.org/licenses/>.  */
  18
  19 /* These macros are used to implement ifunc selection in C.  To implement
  20    an ifunc function, foo, which returns the address of __foo_impl1 or
  21    __foo_impl2:
  22
  23    #define foo __redirect_foo
  24    #include <foo.h>
  25    #undef foo
  26    #define SYMBOL_NAME foo
  27    #include <ifunc-init.h>
  28
  29    extern __typeof (REDIRECT_NAME) OPTIMIZE (impl1) attribute_hidden;
  30    extern __typeof (REDIRECT_NAME) OPTIMIZE (impl2) attribute_hidden;
  31
  32    static inline void *
  33    foo_selector (void)
  34    {
  35      if (condition)
  36       return OPTIMIZE (impl2);
  37
  38      return OPTIMIZE (impl1);
  39    }
  40
  41    libc_ifunc_redirected (__redirect_foo, foo, IFUNC_SELECTOR ());
  42 */
  43
  44 #define PASTER1(x,y)    x##_##y
  45 #define EVALUATOR1(x,y) PASTER1 (x,y)
  46 #define PASTER2(x,y)    __##x##_##y
  47 #define EVALUATOR2(x,y) PASTER2 (x,y)
  48
  49 /* Basically set '__redirect_<symbol>' to use as type definition,
  50    '__<symbol>_<variant>' as the optimized implementation and
  51    '<symbol>_ifunc_selector' as the IFUNC selector.  */
  52 #define REDIRECT_NAME   EVALUATOR1 (__redirect, SYMBOL_NAME)
  53 #define OPTIMIZE(name)  EVALUATOR2 (SYMBOL_NAME, name)
  54 #define IFUNC_SELECTOR  EVALUATOR1 (SYMBOL_NAME, ifunc_selector)