[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 <stdarg.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include <mLib/macros.h>

#include "dispatch.h"

/*----- Intel x86/AMD64 feature probing -----------------------------------*/

#if CPUFAM_X86 || CPUFAM_AMD64

#  define CPUID1D_SSE2 (1u << 26)
#  define CPUID1D_FXSR (1u << 24)
#  define CPUID1C_PCLMUL (1u << 1)
#  define CPUID1C_SSSE3 (1u << 9)
#  define CPUID1C_AESNI (1u << 25)
#  define CPUID1C_AVX (1u << 28)
#  define CPUID1C_RDRAND (1u << 30)

struct cpuid { unsigned a, b, c, d; };
extern int dispatch_x86ish_cpuid(struct cpuid *, unsigned a, unsigned c);
extern int dispatch_x86ish_xmmregisters_p(void);

static void cpuid(struct cpuid *cc, unsigned a, unsigned c)
{
  int rc = dispatch_x86ish_cpuid(cc, a, c);
  if (rc)
    dispatch_debug("CPUID instruction not available");
  else
    dispatch_debug("CPUID(%08x, %08x) -> %08x, %08x, %08x, %08x",
                   a, c, cc->a, cc->b, cc->c, cc->d);
}

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

/* --- @cpuid_features_p@ --- *
 *
 * Arguments:   @unsigned dbits@ = bits to check in EDX
 *              @unsigned cbits@ = bits to check in ECX
 *
 * Returns:     Nonzero if all the requested bits are set in the CPUID result
 *              on leaf 1.
 */

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);
}

/* --- @xmm_registers_available_p@ --- *
 *
 * Arguments:   ---
 *
 * Returns:     Nonzero if the operating system has made the XMM registers
 *              available for use.
 */

static int xmm_registers_available_p(void)
{
  int f = dispatch_x86ish_xmmregisters_p();

  dispatch_debug("XMM registers %savailable", f ? "" : "not ");
  return (f);
}

/* --- @rdrand_works_p@ --- *
 *
 *
 * Arguments:   ---
 *
 * Returns:     Nonzero if the `rdrand' instruction actually works.  Assumes
 *              that it's already been verified to be safe to issue.
 */

#ifdef __GNUC__
static int rdrand(unsigned *x)
{
  int i, rc;
  unsigned _t;

  i = 16;
  __asm__ ("" : "=g" (_t));
  __asm__ ("0: rdrand %2; jc 1f; decl %1; jnz 0b\n"
           "mov $-1, %0; jmp 9f\n"
           "1: movl %2, (%3); xorl %0, %0\n"
           "9:"
           : "=r" (rc), "+r" (i), "+r" (_t)
           : "r" (x)
           : "cc");
  return (rc);
}
#endif

static int rdrand_works_p(void)
{
  unsigned ref, x, i;

  /* Check that it doesn't always give the same answer.  Try four times: this
   * will fail with probability %$2^{-128}$% with a truly random generator,
   * which seems fair enough.
   */
  if (rdrand(&ref)) goto fail;
  for (i = 0; i < 4; i++) {
    if (rdrand(&x)) goto fail;
    if (x != ref) goto not_stuck;
  }
  dispatch_debug("RDRAND always returns 0x%08x!", ref);
  return (0);

not_stuck:
  dispatch_debug("RDRAND instruction looks plausible");
  return (1);

fail:
  dispatch_debug("RDRAND instruction fails too often");
  return (0);
}

#endif

/*----- General feature probing using auxiliary vectors -------------------*/

/* Try to find the system's definitions for auxiliary vector entries. */
#ifdef HAVE_SYS_AUXV_H
#  include <sys/auxv.h>
#endif
#ifdef HAVE_LINUX_AUXVEC_H
#  include <linux/auxvec.h>
#endif
#ifdef HAVE_ASM_HWCAP_H
#  include <asm/hwcap.h>
#endif

/* The type of entries in the auxiliary vector.  I'm assuming that `unsigned
 * long' matches each platform's word length; if this is false then we'll
 * need some host-specific tweaking here.
 */
union auxval { long i; unsigned long u; const void *p; };
struct auxentry { unsigned long type; union auxval value; };

/* Register each CPU family's interest in the auxiliary vector.  Make sure
 * that the necessary entry types are defined.  This is primarily ordered by
 * entry type to minimize duplication.
 */
#if defined(AT_HWCAP) && CPUFAM_ARMEL
#  define WANT_ANY 1
#  define WANT_AT_HWCAP(_) _(AT_HWCAP, u, hwcap)
#endif

#if defined(AT_HWCAP) && CPUFAM_ARM64
#  define WANT_ANY 1
#  define WANT_AT_HWCAP(_) _(AT_HWCAP, u, hwcap)
#endif

#if defined(AT_HWCAP2) && CPUFAM_ARMEL
#  define WANT_ANY 1
#  define WANT_AT_HWCAP2(_) _(AT_HWCAP2, u, hwcap2)
#endif

/* If we couldn't find any interesting entries then we can switch all of this
 * machinery off.  Also do that if we have no means for atomic updates.
 */
#if WANT_ANY && CPU_DISPATCH_P

/* The main output of this section is a bitmask of detected features.  The
 * least significant bit will be set if we've tried to probe.  Always access
 * this using `DISPATCH_LOAD' and `DISPATCH_STORE'.
 */
static unsigned hwcaps = 0;

/* For each potentially interesting type which turned out not to exist or be
 * wanted, define a dummy macro for the sake of the next step.
 */
#ifndef WANT_AT_HWCAP
#  define WANT_AT_HWCAP(_)
#endif
#ifndef WANT_AT_HWCAP2
#  define WANT_AT_HWCAP2(_)
#endif

/* For each CPU family, define two lists.
 *
 *   * `WANTAUX' is a list of the `WANT_AT_MUMBLE' macros which the CPU
 *     family tried to register interest in above.  Each entry contains the
 *     interesting auxiliary vector entry type, the name of the union branch
 *     for its value, and the name of the slot in `struct auxprobe' in which
 *     to store the value.
 *
 *   * `CAPMAP' is a list describing the output features which the CPU family
 *     intends to satisfy from the auxiliary vector.  Each entry contains a
 *     feature name suffix, and the token name (for `check_env').
 */
#if CPUFAM_ARMEL
#  define WANTAUX(_)                                                    \
        WANT_AT_HWCAP(_)                                                \
        WANT_AT_HWCAP2(_)
#  define CAPMAP(_)                                                     \
        _(ARM_VFP, "arm:vfp")                                           \
        _(ARM_NEON, "arm:neon")                                         \
        _(ARM_V4, "arm:v4")                                             \
        _(ARM_D32, "arm:d32")                                           \
        _(ARM_AES, "arm:aes")                                           \
        _(ARM_PMULL, "arm:pmull")
#endif
#if CPUFAM_ARM64
#  define WANTAUX(_)                                                    \
        WANT_AT_HWCAP(_)
#  define CAPMAP(_)                                                     \
        _(ARM_AES, "arm:aes")                                           \
        _(ARM_PMULL, "arm:pmull")
#endif

/* Build the bitmask for `hwcaps' from the `CAPMAP' list. */
enum {
  HFI_PROBED = 0,
#define HFI__ENUM(feat, tok) HFI_##feat,
  CAPMAP(HFI__ENUM)
#undef HFI__ENUM
  HFI__END
};
enum {
  HF_PROBED = 1,
#define HF__FLAG(feat, tok) HF_##feat = 1 << HFI_##feat,
  CAPMAP(HF__FLAG)
#undef HF__FLAG
  HF__END
};

/* Build a structure in which we can capture the interesting data from the
 * auxiliary vector.
 */
#define AUXUTYPE_i long
#define AUXUTYPE_u unsigned long
#define AUXUTYPE_p const void *
struct auxprobe {
#define AUXPROBE__SLOT(type, ubranch, slot) AUXUTYPE_##ubranch slot;
  WANTAUX(AUXPROBE__SLOT)
#undef AUXPROBE_SLOT
};

/* --- @probe_hwcaps@ --- *
 *
 * Arguments:   ---
 *
 * Returns:     ---
 *
 * Use:         Attempt to find the auxiliary vector (which is well hidden)
 *              and discover interesting features from it.
 */

static void probe_hwcaps(void)
{
  unsigned hw = HF_PROBED;
  struct auxprobe probed = { 0 };

  /* Populate `probed' with the information we manage to retrieve from the
   * auxiliary vector.  Slots we couldn't find are left zero-valued.
   */
#if defined(HAVE_GETAUXVAL)
  /* Shiny new libc lets us request individual entry types.  This is almost
   * too easy.
   */
#  define CAP__GET(type, ubranch, slot)                                 \
        probed.slot = (AUXUTYPE_##ubranch)getauxval(type);
  WANTAUX(CAP__GET)
#else
  /* Otherwise we're a bit stuck, really.  Modern Linux kernels make a copy
   * of the vector available in `/procc' so we could try that.
   *
   * The usual place is stuck on the end of the environment vector, but that
   * may well have moved, and we have no way of telling whether it has or
   * whether there was ever an auxiliary vector there at all; so don't do
   * that.
   */
  {
    FILE *fp = 0;
    unsigned char *p = 0, *q = 0;
    const struct auxentry *a;
    size_t sz, off, n;

    /* Open the file and read it into a memory chunk. */
    if ((fp = fopen("/proc/self/auxv", "rb")) == 0) goto clean;
    sz = 4096; off = 0;
    if ((p = malloc(sz)) == 0) goto clean;
    for (;;) {
      n = fread(p + off, 1, sz - off, fp);
      off += n;
      if (off < sz) break;
      sz *= 2; if ((q = realloc(p, sz)) == 0) break;
      p = q;
    }

    /* Work through the vector (or as much of it as we found) and extract the
     * types we're interested in.
     */
    for (a = (const struct auxentry *)p,
           n = sz/sizeof(struct auxentry);
         n--; a++) {
      switch (a->type) {
#define CAP__SWITCH(type, ubranch, slot)                                \
        case type: probed.slot = a->value.ubranch; break;
        WANTAUX(CAP__SWITCH)
        case AT_NULL: goto clean;
      }
    }

  clean:
    if (p) free(p);
    if (fp) fclose(fp);
  }
#endif

  /* Each CPU family now has to pick through what was found and stashed in
   * `probed', and set the appropriate flag bits in `hw'.
   */
#if CPUFAM_ARMEL
  if (probed.hwcap & HWCAP_VFPv3) hw |= HF_ARM_VFP;
  if (probed.hwcap & HWCAP_NEON) hw |= HF_ARM_NEON;
  if (probed.hwcap & HWCAP_VFPD32) hw |= HF_ARM_D32;
  if (probed.hwcap & HWCAP_VFPv4) hw |= HF_ARM_V4;
#  ifdef HWCAP2_AES
  if (probed.hwcap2 & HWCAP2_AES) hw |= HF_ARM_AES;
#  endif
#  ifdef HWCAP2_PMULL
  if (probed.hwcap2 & HWCAP2_PMULL) hw |= HF_ARM_PMULL;
#  endif
#endif
#if CPUFAM_ARM64
  if (probed.hwcap & HWCAP_AES) hw |= HF_ARM_AES;
  if (probed.hwcap & HWCAP_PMULL) hw |= HF_ARM_PMULL;
#endif

  /* Store the bitmask of features we probed for everyone to see. */
  DISPATCH_STORE(hwcaps, hw);

  /* Finally, make a report about the things we found.  (Doing this earlier
   * will pointlessly widen the window in which multiple threads will do the
   * above auxiliary-vector probing.)
   */
#define CAP__DEBUG(feat, tok)                                           \
  dispatch_debug("check auxv for feature `%s': %s", tok,                \
                 hw & HF_##feat ? "available" : "absent");
  CAPMAP(CAP__DEBUG)
#undef CAP__DEBUG
}

/* --- @get_hwcaps@ --- *
 *
 * Arguments:   ---
 *
 * Returns:     A mask of hardware capabilities and other features, as probed
 *              from the auxiliary vector.
 */

static unsigned get_hwcaps(void)
{
  unsigned hw;

  DISPATCH_LOAD(hwcaps, hw);
  if (!(hwcaps & HF_PROBED)) { probe_hwcaps(); DISPATCH_LOAD(hwcaps, hw); }
  return (hw);
}

#endif

/*----- External interface ------------------------------------------------*/

/* --- @dispatch_debug@ --- *
 *
 * Arguments:   @const char *fmt@ = a format string
 *              @...@ = additional arguments
 *
 * Returns:     ---
 *
 * Use:         Writes a formatted message to standard output if dispatch
 *              debugging is enabled.
 */

void dispatch_debug(const char *fmt, ...)
{
  va_list ap;
  const char *e = getenv("CATACOMB_CPUDISPATCH_DEBUG");

  if (e && *e != 'n' && *e != '0') {
    va_start(ap, fmt);
    fputs("Catacomb CPUDISPATCH: ", stderr);
    vfprintf(stderr, fmt, ap);
    fputc('\n', stderr);
    va_end(ap);
  }
}

/* --- @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>

static int IGNORABLE
  feat_debug(const char *ftok, const char *check, int verdict)
{
  if (verdict >= 0) {
    dispatch_debug("feature `%s': %s -> %s", ftok, check,
                   verdict ? "available" : "absent");
  }
  return (verdict);
}

int cpu_feature_p(int feat)
{
  int IGNORABLE f;
  IGNORE(f);
#define CASE_CPUFEAT(feat, ftok, cond) case CPUFEAT_##feat:             \
  if ((f = feat_debug(ftok, "environment override",                     \
                      check_env(ftok))) >= 0)                           \
    return (f);                                                         \
  else                                                                  \
    return (feat_debug(ftok, "runtime probe", cond));

  switch (feat) {
#if CPUFAM_X86 || CPUFAM_AMD64
    CASE_CPUFEAT(X86_SSE2, "x86:sse2",
                 cpuid_features_p(CPUID1D_SSE2, 0) &&
                 xmm_registers_available_p());
    CASE_CPUFEAT(X86_AESNI, "x86:aesni",
                 cpuid_features_p(CPUID1D_SSE2, CPUID1C_AESNI) &&
                 xmm_registers_available_p());
    CASE_CPUFEAT(X86_RDRAND, "x86:rdrand",
                 cpuid_features_p(0, CPUID1C_RDRAND) && rdrand_works_p());
    CASE_CPUFEAT(X86_AVX, "x86:avx",
                 cpuid_features_p(0, CPUID1C_AVX) &&
                 xmm_registers_available_p());
    CASE_CPUFEAT(X86_SSSE3, "x86:ssse3",
                 cpuid_features_p(0, CPUID1C_SSSE3) &&
                 xmm_registers_available_p());
    CASE_CPUFEAT(X86_PCLMUL, "x86:pclmul",
                 cpuid_features_p(0, CPUID1C_PCLMUL) &&
                 xmm_registers_available_p());
#endif
#ifdef CAPMAP
#  define FEATP__CASE(feat, tok)                                        \
        CASE_CPUFEAT(feat, tok, get_hwcaps() & HF_##feat)
    CAPMAP(FEATP__CASE)
#undef FEATP__CASE
#endif
    default:
      dispatch_debug("denying unknown feature %d", feat);
      return (0);
  }
#undef CASE_CPUFEAT
}

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