base/dispatch.c: Add (unused) machinery for probing ELF auxilary vector.

[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 EFLAGS_ID (1u << 21)
#  define CPUID1D_SSE2 (1u << 26)
#  define CPUID1D_FXSR (1u << 24)
#  define CPUID1C_AESNI (1u << 25)

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__
#  if CPUFAM_X86
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);
}
#  else
static __inline__ unsigned long getflags(void)
  { unsigned long f; __asm__ ("pushf; popq %0" : "=g" (f)); return (f); }
static __inline__ unsigned long long setflags(unsigned long f)
{
  unsigned long ff;
  __asm__ ("pushf; pushq %1; popf; pushf; popq %0; popf"
	   : "=g" (ff)
	   : "g" (f));
  return (ff);
}
#  endif
#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) ||
	setflags(f & ~EFLAGS_ID) & EFLAGS_ID) {
    dispatch_debug("CPUID instruction not available");
    return;
  }
  setflags(f);

  /* Alas, EBX is magical in PIC code, so abuse ESI instead.  This isn't
   * pretty, but it works.
   */
#  if CPUFAM_X86
  __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));
#  elif CPUFAM_AMD64
  __asm__ ("pushq %%rbx; cpuid; movl %%ebx, %%esi; popq %%rbx"
	   : "=a" (cc->a), "=S" (cc->b), "=c" (cc->c), "=d" (cc->d)
	   : "a" (a) , "c" (c));
#  else
#    error "I'm confused."
#  endif
  dispatch_debug("CPUID(%08x, %08x) -> %08x, %08x, %08x, %08x",
		 a, c, cc->a, cc->b, cc->c, cc->d);
#else
  dispatch_debug("GNU inline assembler not available; can't CPUID");
#endif
}

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)
{
#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);
#  if CPUFAM_X86
  __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");
#  elif CPUFAM_AMD64
  __asm__ ("movq %%rsp, %%rdx; subq $512, %%rsp; andq $~15, %%rsp\n"
	   "fxsave (%%rsp)\n"
	   "movl 160(%%rsp), %%eax; xorl $0xaaaa5555, 160(%%rsp)\n"
	   "fxrstor (%%rsp); fxsave (%%rsp)\n"
	   "movl 160(%%rsp), %%ecx; movl %%eax, 160(%%rsp)\n"
	   "fxrstor (%%rsp); movq %%rdx, %%rsp\n"
	   "xorl %%ecx, %%eax"
	   : "=a" (f)
	   : /* no inputs */
	   : "%ecx", "%rdx");
#  else
#    error "I'm confused."
#  endif
  dispatch_debug("XMM registers %savailable", f ? "" : "not ");
  return (f);
#else
  dispatch_debug("GNU inline assembler not available; can't check for XMM");
  return (0);
#endif
}

#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>
#else
#  ifdef HAVE_LINUX_AUXVEC_H
#    include <linux/auxvec.h>
#  endif
#  ifdef HAVE_ASM_HWCAP_H
#    include <asm/hwcap.h>
#  endif
#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 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

/* 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').
 */

/* 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, slot, ubranch)					\
	probed.slot.ubranch = (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)
      }
    }

  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'.
   */

  /* 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",
		 xmm_registers_available_p() &&
		 cpuid_features_p(CPUID1D_SSE2, 0));
    CASE_CPUFEAT(X86_AESNI, "x86:aesni",
		 xmm_registers_available_p() &&
		 cpuid_features_p(CPUID1D_SSE2, CPUID1C_AESNI));
#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 -------------------------------------------------*/