base/dispatch.c: Check operating system support for XMM registers.

[catacomb] / base / dispatch.c

/* -*-c-*-
 *
 * CPU-specific dispatch
 *
 * (c) 2015 Straylight/Edgeware
 */

/*----- Licensing notice --------------------------------------------------*
 *
 * This file is part of Catacomb.
 *
 * Catacomb is free software; you can redistribute it and/or modify
 * it under the terms of the GNU Library General Public License as
 * published by the Free Software Foundation; either version 2 of the
 * License, or (at your option) any later version.
 *
 * Catacomb 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 Library General Public License for more details.
 *
 * You should have received a copy of the GNU Library General Public
 * License along with Catacomb; if not, write to the Free
 * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
 * MA 02111-1307, USA.
 */

/*----- Header files ------------------------------------------------------*/

#include "config.h"

#include <ctype.h>
#include <stdlib.h>
#include <string.h>

#include <mLib/macros.h>

#include "dispatch.h"

/*----- Main code ---------------------------------------------------------*/

#ifdef CPUFAM_X86

#define EFLAGS_ID (1u << 21)
#define CPUID1D_SSE2 (1u << 26)
#define CPUID1D_FXSR (1u << 24)

struct cpuid { unsigned a, b, c, d; };

/* --- @cpuid@ --- *
 *
 * Arguments:	@struct cpuid *cc@ = where to write the result
 *		@unsigned a, c@ = EAX and ECX registers to set
 *
 * Returns:	---
 *
 * Use:		Minimal C wrapper around the x86 `CPUID' instruction.  Checks
 *		that the instruction is actually available before invoking
 *		it; fills the output structure with zero if it's not going to
 *		work.
 */

#ifdef __GNUC__
static __inline__ unsigned getflags(void)
  { unsigned f; __asm__ ("pushf; popl %0" : "=g" (f)); return (f); }
static __inline__ unsigned setflags(unsigned f)
{
  unsigned ff;
  __asm__ ("pushf; pushl %1; popf; pushf; popl %0; popf"
	   : "=g" (ff)
	   : "g" (f));
  return (ff);
}
#endif

static void cpuid(struct cpuid *cc, unsigned a, unsigned c)
{
#ifdef __GNUC__
  unsigned f;
#endif

  cc->a = cc->b = cc->c = cc->d = 0;

#ifdef __GNUC__
  /* Stupid dance to detect whether the CPUID instruction is available. */
  f = getflags();
  if (!(setflags(f |  EFLAGS_ID) & EFLAGS_ID)) return;
  if (  setflags(f & ~EFLAGS_ID) & EFLAGS_ID ) return;
  setflags(f);

  /* Alas, EBX is magical in PIC code, so abuse ESI instead.  This isn't
   * pretty, but it works.
   */
  __asm__ ("pushl %%ebx; cpuid; movl %%ebx, %%esi; popl %%ebx"
	   : "=a" (cc->a), "=S" (cc->b), "=c" (cc->c), "=d" (cc->d)
	   : "a" (a) , "c" (c));
#endif
}

static unsigned cpuid_maxleaf(void)
  { struct cpuid c; cpuid(&c, 0, 0); return (c.a); }

static int cpuid_features_p(unsigned dbits, unsigned cbits)
{
  struct cpuid c;
  if (cpuid_maxleaf() < 1) return (0);
  cpuid(&c, 1, 0);
  return ((c.d & dbits) == dbits && (c.c & cbits) == cbits);
}

static int xmm_registers_available_p(void)
{
#ifdef __GNUC__
  unsigned f;
  /* This hack is by Agner Fog.  Use FXSAVE/FXRSTOR to figure out whether the
   * XMM registers are actually alive.
   */
  if (!cpuid_features_p(CPUID1D_FXSR, 0)) return (0);
  __asm__ ("movl %%esp, %%edx; subl $512, %%esp; andl $~15, %%esp\n"
	   "fxsave (%%esp)\n"
	   "movl 160(%%esp), %%eax; xorl $0xaaaa5555, 160(%%esp)\n"
	   "fxrstor (%%esp); fxsave (%%esp)\n"
	   "movl 160(%%esp), %%ecx; movl %%eax, 160(%%esp)\n"
	   "fxrstor (%%esp); movl %%edx, %%esp\n"
	   "xorl %%ecx, %%eax"
	   : "=a" (f)
	   : /* no inputs */
	   : "%ecx", "%edx");
  return (f);
#else
  return (0);
#endif
}

#endif

/* --- @check_env@ --- *
 *
 * Arguments:	@const char *ftok@ = feature token
 *
 * Returns:	Zero if the feature is forced off; positive if it's forced
 *		on; negative if the user hasn't decided.
 *
 * Use:		Checks the environment variable `CATACOMB_CPUFEAT' for the
 *		feature token @ftok@.  The variable, if it exists, should be
 *		a space-separated sequence of `+tok' and `-tok' items.  These
 *		tokens may end in `*', which matches any suffix.
 */

static int IGNORABLE check_env(const char *ftok)
{
  const char *p, *q, *pp;
  int d;

  p = getenv("CATACOMB_CPUFEAT");
  if (!p) return (-1);

  for (;;) {
    while (isspace((unsigned char)*p)) p++;
    if (!*p) return (-1);
    switch (*p) {
      case '+': d = +1; p++; break;
      case '-': d =  0; p++; break;
      default:  d = -1;      break;
    }
    for (q = p; *q && !isspace((unsigned char)*q); q++);
    if (d >= 0) {
      for (pp = ftok; p < q && *pp && *p == *pp; p++, pp++);
      if ((p == q && !*pp) || (*p == '*' && p + 1 == q)) return (d);
    }
    p = q;
  }
  return (-1);
}

/* --- @cpu_feature_p@ --- *
 *
 * Arguments:	@unsigned feat@ = a @CPUFEAT_...@ code
 *
 * Returns:	Nonzero if the feature is available.
 */

#include <stdio.h>

int cpu_feature_p(int feat)
{
  int IGNORABLE f;
  IGNORE(f);
#define CHECK_ENV(ftok)							\
  do { if ((f = check_env(ftok)) >= 0) return (f); } while (0)

  switch (feat) {
#ifdef CPUFAM_X86
    case CPUFEAT_X86_SSE2: {
      CHECK_ENV("x86:sse2");
      return (xmm_registers_available_p() &&
	      cpuid_features_p(CPUID1D_SSE2, 0));
    }
#endif
    default:
      return (0);
  }
#undef CHECK_ENV
}

/*----- That's all, folks -------------------------------------------------*/