1  /* IFUNC generic definitions.
       2     This file is part of the GNU C Library.
       3     Copyright (C) 2017-2023 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     <https://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 IFUNC_SELECTOR	EVALUATOR1 (SYMBOL_NAME, ifunc_selector)
      54  #define OPTIMIZE1(name)	EVALUATOR1 (SYMBOL_NAME, name)
      55  #define OPTIMIZE2(name)	EVALUATOR2 (SYMBOL_NAME, name)
      56  /* Default is to use OPTIMIZE2.  */
      57  #define OPTIMIZE(name)	OPTIMIZE2(name)