1/* IFUNC generic definitions.
2 This file is part of the GNU C Library.
3 Copyright (C) 2017-2021 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 OPTIMIZE(name) EVALUATOR2 (SYMBOL_NAME, name)
54#define IFUNC_SELECTOR EVALUATOR1 (SYMBOL_NAME, ifunc_selector)
55