mdw@git.distorted.org.uk Git - catacomb/blob - base/dispatch.c

   1 /* -*-c-*-
   2  *
   3  * CPU-specific dispatch
   4  *
   5  * (c) 2015 Straylight/Edgeware
   6  */
   7
   8 /*----- Licensing notice --------------------------------------------------*
   9  *
  10  * This file is part of Catacomb.
  11  *
  12  * Catacomb is free software; you can redistribute it and/or modify
  13  * it under the terms of the GNU Library General Public License as
  14  * published by the Free Software Foundation; either version 2 of the
  15  * License, or (at your option) any later version.
  16  *
  17  * Catacomb is distributed in the hope that it will be useful,
  18  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  19  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  20  * GNU Library General Public License for more details.
  21  *
  22  * You should have received a copy of the GNU Library General Public
  23  * License along with Catacomb; if not, write to the Free
  24  * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
  25  * MA 02111-1307, USA.
  26  */
  27
  28 /*----- Header files ------------------------------------------------------*/
  29
  30 #include "config.h"
  31
  32 #include <ctype.h>
  33 #include <stdlib.h>
  34 #include <string.h>
  35
  36 #include <mLib/macros.h>
  37
  38 #include "dispatch.h"
  39
  40 /*----- Main code ---------------------------------------------------------*/
  41
  42 #ifdef CPUFAM_X86
  43
  44 #define EFLAGS_ID (1u << 21)
  45 #define CPUID1D_SSE2 (1u << 26)
  46
  47 struct cpuid { unsigned a, b, c, d; };
  48
  49 /* --- @cpuid@ --- *
  50  *
  51  * Arguments:   @struct cpuid *cc@ = where to write the result
  52  *              @unsigned a, c@ = EAX and ECX registers to set
  53  *
  54  * Returns:     ---
  55  *
  56  * Use:         Minimal C wrapper around the x86 `CPUID' instruction.  Checks
  57  *              that the instruction is actually available before invoking
  58  *              it; fills the output structure with zero if it's not going to
  59  *              work.
  60  */
  61
  62 #ifdef __GNUC__
  63 static __inline__ unsigned getflags(void)
  64   { unsigned f; __asm__ ("pushf; popl %0" : "=g" (f)); return (f); }
  65 static __inline__ unsigned setflags(unsigned f)
  66 {
  67   unsigned ff;
  68   __asm__ ("pushf; pushl %1; popf; pushf; popl %0; popf"
  69            : "=g" (ff)
  70            : "g" (f));
  71   return (ff);
  72 }
  73 #endif
  74
  75 static void cpuid(struct cpuid *cc, unsigned a, unsigned c)
  76 {
  77 #ifdef __GNUC__
  78   unsigned f;
  79 #endif
  80
  81   cc->a = cc->b = cc->c = cc->d = 0;
  82
  83 #ifdef __GNUC__
  84   /* Stupid dance to detect whether the CPUID instruction is available. */
  85   f = getflags();
  86   if (!(setflags(f |  EFLAGS_ID) & EFLAGS_ID)) return;
  87   if (  setflags(f & ~EFLAGS_ID) & EFLAGS_ID ) return;
  88   setflags(f);
  89
  90   /* Alas, EBX is magical in PIC code, so abuse ESI instead.  This isn't
  91    * pretty, but it works.
  92    */
  93   __asm__ ("pushl %%ebx; cpuid; movl %%ebx, %%esi; popl %%ebx"
  94            : "=a" (cc->a), "=S" (cc->b), "=c" (cc->c), "=d" (cc->d)
  95            : "a" (a) , "c" (c));
  96 #endif
  97 }
  98
  99 static unsigned cpuid_maxleaf(void)
 100   { struct cpuid c; cpuid(&c, 0, 0); return (c.a); }
 101
 102 static int cpuid_features_p(unsigned dbits, unsigned cbits)
 103 {
 104   struct cpuid c;
 105   if (cpuid_maxleaf() < 1) return (0);
 106   cpuid(&c, 1, 0);
 107   return ((c.d & dbits) == dbits && (c.c & cbits) == cbits);
 108 }
 109
 110 #endif
 111
 112 /* --- @check_env@ --- *
 113  *
 114  * Arguments:   @const char *ftok@ = feature token
 115  *
 116  * Returns:     Zero if the feature is forced off; positive if it's forced
 117  *              on; negative if the user hasn't decided.
 118  *
 119  * Use:         Checks the environment variable `CATACOMB_CPUFEAT' for the
 120  *              feature token @ftok@.  The variable, if it exists, should be
 121  *              a space-separated sequence of `+tok' and `-tok' items.  These
 122  *              tokens may end in `*', which matches any suffix.
 123  */
 124
 125 static int IGNORABLE check_env(const char *ftok)
 126 {
 127   const char *p, *q, *pp;
 128   int d;
 129
 130   p = getenv("CATACOMB_CPUFEAT");
 131   if (!p) return (-1);
 132
 133   for (;;) {
 134     while (isspace((unsigned char)*p)) p++;
 135     if (!*p) return (-1);
 136     switch (*p) {
 137       case '+': d = +1; p++; break;
 138       case '-': d =  0; p++; break;
 139       default:  d = -1;      break;
 140     }
 141     for (q = p; *q && !isspace((unsigned char)*q); q++);
 142     if (d >= 0) {
 143       for (pp = ftok; p < q && *pp && *p == *pp; p++, pp++);
 144       if ((p == q && !*pp) || (*p == '*' && p + 1 == q)) return (d);
 145     }
 146     p = q;
 147   }
 148   return (-1);
 149 }
 150
 151 /* --- @cpu_feature_p@ --- *
 152  *
 153  * Arguments:   @unsigned feat@ = a @CPUFEAT_...@ code
 154  *
 155  * Returns:     Nonzero if the feature is available.
 156  */
 157
 158 #include <stdio.h>
 159
 160 int cpu_feature_p(int feat)
 161 {
 162   int IGNORABLE f;
 163   IGNORE(f);
 164 #define CHECK_ENV(ftok)                                                 \
 165   do { if ((f = check_env(ftok)) >= 0) return (f); } while (0)
 166
 167   switch (feat) {
 168 #ifdef CPUFAM_X86
 169     case CPUFEAT_X86_SSE2: {
 170       CHECK_ENV("x86:sse2");
 171       return (cpuid_features_p(CPUID1D_SSE2, 0));
 172     }
 173 #endif
 174     default:
 175       return (0);
 176   }
 177 #undef CHECK_ENV
 178 }
 179
 180 /*----- That's all, folks -------------------------------------------------*/