libitm/config/x86/target.h

/* Copyright (C) 2008-2021 Free Software Foundation, Inc.
   Contributed by Richard Henderson <rth@redhat.com>.

   This file is part of the GNU Transactional Memory Library (libitm).

   Libitm 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.

   Libitm 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/>.  */

// We'll be using some of the cpu builtins, and their associated types.
#include <x86intrin.h>
#include <cpuid.h>

namespace GTM HIDDEN {

/* ??? This doesn't work for Win64.  */
typedef struct gtm_jmpbuf
{
  void *cfa;
#ifdef __x86_64__
  unsigned long long rbx;
  unsigned long long rbp;
  unsigned long long r12;
  unsigned long long r13;
  unsigned long long r14;
  unsigned long long r15;
  unsigned long long ssp;
  unsigned long long rip;
#else
  unsigned long ebx;
  unsigned long esi;
  unsigned long edi;
  unsigned long ebp;
  unsigned long ssp;
  unsigned long eip;
#endif
} gtm_jmpbuf;

/* x86 doesn't require strict alignment for the basic types.  */
#define STRICT_ALIGNMENT 0

/* The size of one line in hardware caches (in bytes). */
#define HW_CACHELINE_SIZE 64


static inline void
cpu_relax (void)
{
  __builtin_ia32_pause ();
}

// Use Intel RTM if supported by the assembler.
// See gtm_thread::begin_transaction for how these functions are used.
#ifdef HAVE_AS_RTM
#define USE_HTM_FASTPATH
#ifdef __x86_64__
// Use the custom fastpath in ITM_beginTransaction.
#define HTM_CUSTOM_FASTPATH
#endif

static inline bool
htm_available ()
{
  const unsigned cpuid_rtm = bit_RTM;
  unsigned vendor;

  if (__get_cpuid_max (0, &vendor) >= 7)
    {
      unsigned a, b, c, d;
      unsigned family;

      __cpuid (1, a, b, c, d);
      family = (a >> 8) & 0x0f;
      /* TSX is broken on some processors.  TSX can be disabled by microcode,
	 but we cannot reliably detect whether the microcode has been
	 updated.  Therefore, do not report availability of TSX on these
	 processors.  We use the same approach here as in glibc (see
	 https://sourceware.org/ml/libc-alpha/2016-12/msg00470.html).  */
      if (vendor == signature_INTEL_ebx && family == 0x06)
	{
	  unsigned model = ((a >> 4) & 0x0f) + ((a >> 12) & 0xf0);
	  unsigned stepping = a & 0x0f;
	  if (model == 0x3c
	      /* Xeon E7 v3 has correct TSX if stepping >= 4.  */
	      || (model == 0x3f && stepping < 4)
	      || model == 0x45
	      || model == 0x46)
	    return false;
	}

      __cpuid_count (7, 0, a, b, c, d);
      if (b & cpuid_rtm)
	return true;
    }
  return false;
}

static inline uint32_t
htm_init ()
{
  // Maximum number of times we try to execute a transaction as a HW
  // transaction.
  // ??? Why 2?  Any offline or runtime tuning necessary?
  return htm_available () ? 2 : 0;
}

static inline uint32_t
htm_begin ()
{
  return _xbegin();
}

static inline bool
htm_begin_success (uint32_t begin_ret)
{
  return begin_ret == _XBEGIN_STARTED;
}

static inline void
htm_commit ()
{
  _xend();
}

static inline void
htm_abort ()
{
  // ??? According to a yet unpublished ABI rule, 0xff is reserved and
  // supposed to signal a busy lock.  Source: andi.kleen@intel.com
  _xabort(0xff);
}

static inline bool
htm_abort_should_retry (uint32_t begin_ret)
{
  return begin_ret & _XABORT_RETRY;
}

/* Returns true iff a hardware transaction is currently being executed.  */
static inline bool
htm_transaction_active ()
{
  return _xtest() != 0;
}
#endif


} // namespace GTM