sysdeps/x86/dl-get-cpu-features.c

   1 /* Initialize CPU feature data via IFUNC relocation.
   2    Copyright (C) 2015-2020 Free Software Foundation, Inc.
   3
   4    The GNU C Library is free software; you can redistribute it and/or
   5    modify it under the terms of the GNU Lesser General Public
   6    License as published by the Free Software Foundation; either
   7    version 2.1 of the License, or (at your option) any later version.
   8
   9    The GNU C Library is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12    Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser General Public
  15    License along with the GNU C Library; if not, see
  16    <https://www.gnu.org/licenses/>.  */
  17
  18
  19 #include <ldsodefs.h>
  20
  21 #ifdef SHARED
  22 # include <cpu-features.c>
  23
  24 /* NB: Normally, DL_PLATFORM_INIT calls init_cpu_features to initialize
  25    CPU features in dynamic executable.  But when loading ld.so inside of
  26    static executable, DL_PLATFORM_INIT isn't called and IFUNC relocation
  27    is used to call init_cpu_features.  In static executable, it is called
  28    once by IFUNC relocation.  In dynamic executable, it is called twice
  29    by DL_PLATFORM_INIT and by IFUNC relocation.  */
  30 extern void __x86_cpu_features (void) attribute_hidden;
  31 const void (*__x86_cpu_features_p) (void) attribute_hidden
  32   = __x86_cpu_features;
  33
  34 void
  35 _dl_x86_init_cpu_features (void)
  36 {
  37   struct cpu_features *cpu_features = __get_cpu_features ();
  38   if (cpu_features->basic.kind == arch_kind_unknown)
  39     init_cpu_features (cpu_features);
  40 }
  41
  42 __ifunc (__x86_cpu_features, __x86_cpu_features, NULL, void,
  43          _dl_x86_init_cpu_features);
  44 #endif
  45
  46 #undef __x86_get_cpu_features
  47
  48 const struct cpu_features *
  49 __x86_get_cpu_features (unsigned int max)
  50 {
  51   if (max > COMMON_CPUID_INDEX_MAX)
  52     return NULL;
  53   return &GLRO(dl_x86_cpu_features);
  54 }