sysdeps/unix/sysv/linux/powerpc/cpu-features.c

   1 /* Initialize cpu feature data.  PowerPC version.
   2    Copyright (C) 2017-2023 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   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 #include <array_length.h>
  20 #include <stdint.h>
  21 #include <cpu-features.h>
  22 #include <elf/dl-tunables.h>
  23 #include <unistd.h>
  24 #include <string.h>
  25
  26 static void
  27 TUNABLE_CALLBACK (set_hwcaps) (tunable_val_t *valp)
  28 {
  29   /* The current IFUNC selection is always using the most recent
  30      features which are available via AT_HWCAP or AT_HWCAP2.  But in
  31      some scenarios it is useful to adjust this selection.
  32
  33      The environment variable:
  34
  35      GLIBC_TUNABLES=glibc.cpu.hwcaps=-xxx,yyy,....
  36
  37      Can be used to enable HWCAP/HWCAP2 feature yyy, disable HWCAP/HWCAP2
  38      feature xxx, where the feature name is case-sensitive and has to match
  39      the ones mentioned in the file{sysdeps/powerpc/dl-procinfo.c}. */
  40
  41   /* Copy the features from dl_powerpc_cpu_features, which contains the
  42      features provided by AT_HWCAP and AT_HWCAP2.  */
  43   struct cpu_features *cpu_features = &GLRO(dl_powerpc_cpu_features);
  44   unsigned long int tcbv_hwcap = cpu_features->hwcap;
  45   unsigned long int tcbv_hwcap2 = cpu_features->hwcap2;
  46   const char *token = valp->strval;
  47   do
  48     {
  49       const char *token_end, *feature;
  50       bool disable;
  51       size_t token_len, i, feature_len, offset = 0;
  52       /* Find token separator or end of string.  */
  53       for (token_end = token; *token_end != ','; token_end++)
  54         if (*token_end == '\0')
  55           break;
  56
  57       /* Determine feature.  */
  58       token_len = token_end - token;
  59       if (*token == '-')
  60         {
  61           disable = true;
  62           feature = token + 1;
  63           feature_len = token_len - 1;
  64         }
  65       else
  66         {
  67           disable = false;
  68           feature = token;
  69           feature_len = token_len;
  70         }
  71       for (i = 0; i < array_length (hwcap_tunables); ++i)
  72         {
  73           const char *hwcap_name = hwcap_names + offset;
  74           size_t hwcap_name_len = strlen (hwcap_name);
  75           /* Check the tunable name on the supported list.  */
  76           if (hwcap_name_len == feature_len
  77               && memcmp (feature, hwcap_name, feature_len) == 0)
  78             {
  79               /* Update the hwcap and hwcap2 bits.  */
  80               if (disable)
  81                 {
  82                   /* Id is 1 for hwcap2 tunable.  */
  83                   if (hwcap_tunables[i].id)
  84                     cpu_features->hwcap2 &= ~(hwcap_tunables[i].mask);
  85                   else
  86                     cpu_features->hwcap &= ~(hwcap_tunables[i].mask);
  87                 }
  88               else
  89                 {
  90                   /* Enable the features and also check that no unsupported
  91                      features were enabled by user.  */
  92                   if (hwcap_tunables[i].id)
  93                     cpu_features->hwcap2 |= (tcbv_hwcap2 & hwcap_tunables[i].mask);
  94                   else
  95                     cpu_features->hwcap |= (tcbv_hwcap & hwcap_tunables[i].mask);
  96                 }
  97               break;
  98             }
  99           offset += hwcap_name_len + 1;
 100         }
 101         token += token_len;
 102         /* ... and skip token separator for next round.  */
 103         if (*token == ',')
 104           token++;
 105     }
 106   while (*token != '\0');
 107 }
 108
 109 static inline void
 110 init_cpu_features (struct cpu_features *cpu_features, uint64_t hwcaps[])
 111 {
 112   /* Fill the cpu_features with the supported hwcaps
 113      which are set by __tcb_parse_hwcap_and_convert_at_platform.  */
 114   cpu_features->hwcap = hwcaps[0];
 115   cpu_features->hwcap2 = hwcaps[1];
 116   /* Default is to use aligned memory access on optimized function unless
 117      tunables is enable, since for this case user can explicit disable
 118      unaligned optimizations.  */
 119   int32_t cached_memfunc = TUNABLE_GET (glibc, cpu, cached_memopt, int32_t,
 120                                         NULL);
 121   cpu_features->use_cached_memopt = (cached_memfunc > 0);
 122   TUNABLE_GET (glibc, cpu, hwcaps, tunable_val_t *,
 123                TUNABLE_CALLBACK (set_hwcaps));
 124 }