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

   1 /* Initialize cpu feature data.  PowerPC version.
   2    Copyright (C) 2017-2024 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 <dl-tunables-parse.h>
  24 #include <unistd.h>
  25 #include <string.h>
  26
  27 static void
  28 TUNABLE_CALLBACK (set_hwcaps) (tunable_val_t *valp)
  29 {
  30   /* The current IFUNC selection is always using the most recent
  31      features which are available via AT_HWCAP or AT_HWCAP2.  But in
  32      some scenarios it is useful to adjust this selection.
  33
  34      The environment variable:
  35
  36      GLIBC_TUNABLES=glibc.cpu.hwcaps=-xxx,yyy,....
  37
  38      Can be used to enable HWCAP/HWCAP2 feature yyy, disable HWCAP/HWCAP2
  39      feature xxx, where the feature name is case-sensitive and has to match
  40      the ones mentioned in the file{sysdeps/powerpc/dl-procinfo.c}. */
  41
  42   /* Copy the features from dl_powerpc_cpu_features, which contains the
  43      features provided by AT_HWCAP and AT_HWCAP2.  */
  44   struct cpu_features *cpu_features = &GLRO(dl_powerpc_cpu_features);
  45   unsigned long int tcbv_hwcap = cpu_features->hwcap;
  46   unsigned long int tcbv_hwcap2 = cpu_features->hwcap2;
  47
  48   struct tunable_str_comma_state_t ts;
  49   tunable_str_comma_init (&ts, valp);
  50
  51   struct tunable_str_comma_t t;
  52   while (tunable_str_comma_next (&ts, &t))
  53     {
  54       if (t.len == 0)
  55         continue;
  56
  57       size_t offset = 0;
  58       for (int i = 0; i < array_length (hwcap_tunables); ++i)
  59         {
  60           const char *hwcap_name = hwcap_names + offset;
  61           size_t hwcap_name_len = strlen (hwcap_name);
  62           /* Check the tunable name on the supported list.  */
  63           if (tunable_str_comma_strcmp (&t, hwcap_name, hwcap_name_len))
  64             {
  65               /* Update the hwcap and hwcap2 bits.  */
  66               if (t.disable)
  67                 {
  68                   /* Id is 1 for hwcap2 tunable.  */
  69                   if (hwcap_tunables[i].id)
  70                     cpu_features->hwcap2 &= ~(hwcap_tunables[i].mask);
  71                   else
  72                     cpu_features->hwcap &= ~(hwcap_tunables[i].mask);
  73                 }
  74               else
  75                 {
  76                   /* Enable the features and also check that no unsupported
  77                      features were enabled by user.  */
  78                   if (hwcap_tunables[i].id)
  79                     cpu_features->hwcap2 |= (tcbv_hwcap2 & hwcap_tunables[i].mask);
  80                   else
  81                     cpu_features->hwcap |= (tcbv_hwcap & hwcap_tunables[i].mask);
  82                 }
  83               break;
  84             }
  85           offset += hwcap_name_len + 1;
  86         }
  87     }
  88 }
  89
  90 static inline void
  91 init_cpu_features (struct cpu_features *cpu_features, uint64_t hwcaps[])
  92 {
  93   /* Fill the cpu_features with the supported hwcaps
  94      which are set by __tcb_parse_hwcap_and_convert_at_platform.  */
  95   cpu_features->hwcap = hwcaps[0];
  96   cpu_features->hwcap2 = hwcaps[1];
  97   cpu_features->hwcap3 = hwcaps[2];
  98   cpu_features->hwcap4 = hwcaps[3];
  99   /* Default is to use aligned memory access on optimized function unless
 100      tunables is enable, since for this case user can explicit disable
 101      unaligned optimizations.  */
 102   int32_t cached_memfunc = TUNABLE_GET (glibc, cpu, cached_memopt, int32_t,
 103                                         NULL);
 104   cpu_features->use_cached_memopt = (cached_memfunc > 0);
 105   TUNABLE_GET (glibc, cpu, hwcaps, tunable_val_t *,
 106                TUNABLE_CALLBACK (set_hwcaps));
 107 }