libatomic/config/linux/aarch64/host-config.h

/* Copyright (C) 2017-2026 Free Software Foundation, Inc.

   This file is part of the GNU Atomic Library (libatomic).

   Libatomic is free software; you can redistribute it and/or modify it
   under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 3 of the License, or
   (at your option) any later version.

   Libatomic is distributed in the hope that it will be useful, but WITHOUT ANY
   WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
   FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
   more details.

   Under Section 7 of GPL version 3, you are granted additional
   permissions described in the GCC Runtime Library Exception, version
   3.1, as published by the Free Software Foundation.

   You should have received a copy of the GNU General Public License and
   a copy of the GCC Runtime Library Exception along with this program;
   see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
   <http://www.gnu.org/licenses/>.  */

#if HAVE_IFUNC
#include <sys/auxv.h>

#ifndef HWCAP_ATOMICS
# define HWCAP_ATOMICS	(1 << 8)
#endif
#ifndef HWCAP_CPUID
# define HWCAP_CPUID	(1 << 11)
#endif
#ifndef HWCAP_USCAT
# define HWCAP_USCAT	(1 << 25)
#endif
#ifndef HWCAP2_LRCPC3
# define HWCAP2_LRCPC3	(1UL << 46)
#endif
#ifndef HWCAP2_LSE128
# define HWCAP2_LSE128	(1UL << 47)
#endif

/* The following struct is ABI-correct description of the 2nd argument for an
   ifunc resolver as per SYSVABI spec (see link below).  It is safe to extend
   it with new fields.  The ifunc resolver implementations must always check
   the runtime size of the buffer using the value in the _size field.
   https://github.com/ARM-software/abi-aa/blob/main/sysvabi64/sysvabi64.rst.  */
typedef struct __ifunc_arg_t {
  unsigned long _size;
  unsigned long _hwcap;
  unsigned long _hwcap2;
  unsigned long _hwcap3;
  unsigned long _hwcap4;
} __ifunc_arg_t;

# define _IFUNC_ARG_HWCAP (1ULL << 62)

/* From the file which imported `host-config.h' we can ascertain which
   architectural extension provides relevant atomic support.  From this,
   we can proceed to tweak the ifunc selector behavior.  */
#if defined (LAT_CAS_N)
# define LSE_ATOP
#elif defined (LAT_LOAD_N) || defined (LAT_STORE_N)
# define LSE2_LRCPC3_ATOP
#elif defined (LAT_EXCH_N) || defined (LAT_FIOR_N) || defined (LAT_FAND_N)
# define LSE128_ATOP
#endif

# if N == 16
#  if defined (LSE_ATOP)
#   define IFUNC_NCOND(N)	1
#   define IFUNC_COND_1	(hwcap & HWCAP_ATOMICS)
#  elif defined (LSE2_LRCPC3_ATOP)
#   define IFUNC_NCOND(N)	2
#   define IFUNC_COND_1	(has_rcpc3 (hwcap, features))
#   define IFUNC_COND_2	(has_lse2 (hwcap, features))
#  elif defined (LSE128_ATOP)
#   define IFUNC_NCOND(N)	1
#   define IFUNC_COND_1	(has_lse128 (hwcap, features))
#  else
#   define IFUNC_NCOND(N)	0
#   define IFUNC_ALT		1
#  endif
# else
#  define IFUNC_COND_1		(hwcap & HWCAP_ATOMICS)
#  define IFUNC_NCOND(N)	1
# endif

#define MIDR_IMPLEMENTOR(midr)	(((midr) >> 24) & 255)
#define MIDR_PARTNUM(midr)	(((midr) >> 4) & 0xfff)

static inline bool
has_lse2 (unsigned long hwcap, const __ifunc_arg_t *features)
{
  /* Check for LSE2.  */
  if (hwcap & HWCAP_USCAT)
    return true;

  /* If LSE and CPUID are supported, check MIDR.  */
  if (hwcap & HWCAP_CPUID && hwcap & HWCAP_ATOMICS)
    {
      unsigned long midr;
      asm volatile ("mrs %0, midr_el1" : "=r" (midr));

      /* Neoverse N1 supports atomic 128-bit load/store.  */
      return MIDR_IMPLEMENTOR (midr) == 'A' && MIDR_PARTNUM (midr) == 0xd0c;
    }

  return false;
}

/* LSE128 atomic support encoded in ID_AA64ISAR0_EL1.Atomic, bits[23:20].
   The minimum value for LSE128 is 0b0011.  */

#define AT_FEAT_FIELD(isar0)	(((isar0) >> 20) & 15)

static inline bool
has_lse128 (unsigned long hwcap, const __ifunc_arg_t *features)
{
  if (hwcap & _IFUNC_ARG_HWCAP && features->_hwcap2 & HWCAP2_LSE128)
    return true;

  /* If LSE2 and CPUID are supported, check for LSE128.  */
  if (hwcap & HWCAP_CPUID && hwcap & HWCAP_USCAT)
    {
      unsigned long isar0;
      asm volatile ("mrs %0, ID_AA64ISAR0_EL1" : "=r" (isar0));
      return AT_FEAT_FIELD (isar0) >= 3;
    }

  return false;
}

/* LRCPC atomic support encoded in ID_AA64ISAR1_EL1.Atomic, bits[23:20].
   The minimum value for LRCPC3 is 0b0011.  */

static inline bool
has_rcpc3 (unsigned long hwcap, const __ifunc_arg_t *features)
{
  /* LSE2 is a prerequisite for atomic LDIAPP/STILP - check HWCAP_USCAT since
     has_lse2 is more expensive and Neoverse N1 does not have LRCPC3. */
  if (!(hwcap & HWCAP_USCAT))
    return false;

  if (hwcap & _IFUNC_ARG_HWCAP && features->_hwcap2 & HWCAP2_LRCPC3)
    return true;

  if (hwcap & HWCAP_CPUID)
    {
      unsigned long isar1;
      asm volatile ("mrs %0, ID_AA64ISAR1_EL1" : "=r" (isar1));
      return AT_FEAT_FIELD (isar1) >= 3;
    }

  return false;
}

#endif /* HAVE_IFUNC */

/* All 128-bit atomic functions are defined in aarch64/atomic_16.S.  */
#if N == 16
# define DONE 1
# if !HAVE_IFUNC
#  define IFUNC_ALT 1
# endif
#endif

#include_next <host-config.h>