/src/wireshark/wsutil/ws_cpuid.h

Source
/** @file
 * Get the CPU info on x86 processors that support it
 *
 * Wireshark - Network traffic analyzer
 * By Gerald Combs <gerald@wireshark.org>
 * Copyright 1998 Gerald Combs
 *
 * SPDX-License-Identifier: GPL-2.0-or-later
 */

/*
 * Get CPU info on platforms where the x86 cpuid instruction can be used.
 *
 * Skip 32-bit versions for GCC and Clang, as older IA-32 processors don't
 * have cpuid.
 *
 * Intel has documented the CPUID instruction in the "Intel(r) 64 and IA-32
 * Architectures Developer's Manual" at
 *
 * https://www.intel.com/content/www/us/en/architecture-and-technology/64-ia-32-architectures-software-developer-vol-2a-manual.html
 *
 * The ws_cpuid() routine will return 0 if cpuinfo isn't available, including
 * on non-x86 platforms and on 32-bit x86 platforms with GCC and Clang, as
 * well as non-MSVC and non-GCC-or-Clang platforms.
 *
 * The "selector" argument to ws_cpuid() is the "initial EAX value" for the
 * instruction.  The initial ECX value is 0.
 *
 * The "CPUInfo" argument points to 4 32-bit values into which the
 * resulting values of EAX, EBX, ECX, and EDX are store, in order.
 */

#include "ws_attributes.h"

#include <inttypes.h>
#include <stdbool.h>

/**
 * @def ws_cpuid
 * @brief Execute the x86 CPUID instruction with the given selector.
 *
 * Retrieves CPU information by executing the CPUID instruction with the specified
 * selector. The results are stored in the `CPUInfo` array as
 * EAX, EBX, ECX, and EDX, respectively.
 *
 * @param CPUInfo   Pointer to an array of four uint32_t values to receive
 *                  EAX, EBX, ECX, and EDX results, in that order.
 * @param selector  Initial EAX value for the CPUID instruction.
 * @return          true if cpuinfo is available, otherwise 0.
 */


#if defined(_MSC_VER)     /* MSVC */

/*
 * XXX - do the same IA-32 (which doesn't have CPUID prior to some versions
 * of the 80486 and all versions of the 80586^Woriginal Pentium) vs.
 * x86-64 (which always has CPUID) stuff that we do with GCC/Clang?
 *
 * You will probably not be happy running current versions of Wireshark
 * on an 80386 or 80486 machine, and we're dropping support for IA-32
 * on Windows anyway, so the answer is probably "no".
 */
#if defined(_M_IX86) || defined(_M_X64)
static bool
ws_cpuid(uint32_t *CPUInfo, uint32_t selector)
{
  /* https://docs.microsoft.com/en-us/cpp/intrinsics/cpuid-cpuidex */

  CPUInfo[0] = CPUInfo[1] = CPUInfo[2] = CPUInfo[3] = 0;
  __cpuid((int *) CPUInfo, selector);
  /* XXX, how to check if it's supported on MSVC? just in case clear all flags above */
  return true;
}
#else /* not x86 */
static bool
ws_cpuid(uint32_t *CPUInfo _U_, int selector _U_)
{
  /* Not x86, so no cpuid instruction */
  return false;
}
#endif

#elif defined(__GNUC__)  /* GCC/clang */

#if defined(__x86_64__)

/**
 * @brief Execute a CPUID query on the current processor.
 *
 * @param CPUInfo  Output array of four 32-bit registers (EAX, EBX, ECX, EDX).
 * @param selector The CPUID leaf (function ID) to query.
 * @return true if the query was successful, false if unsupported.
 */
static inline bool
ws_cpuid(uint32_t *CPUInfo, int selector)
{
  __asm__ __volatile__("cpuid"
            : "=a" (CPUInfo[0]),
              "=b" (CPUInfo[1]),
              "=c" (CPUInfo[2]),
              "=d" (CPUInfo[3])
            : "a" (selector),
              "c" (0));
  return true;
}
#elif defined(__i386__)

/**
 * @brief Execute a CPUID query on the current processor.
 *
 * @param CPUInfo  Output array of four 32-bit registers (EAX, EBX, ECX, EDX).
 * @param selector The CPUID leaf (function ID) to query.
 * @return true if the query was successful, false if unsupported.
 */
static bool
ws_cpuid(uint32_t *CPUInfo _U_, int selector _U_)
{
  /*
   * TODO: need a test if older processors have the cpuid instruction.
   *
   * The correct way to test for this, according to the Intel64/IA-32
   * documentation from Intel, in section 17.1 "USING THE CPUID
   * INSTRUCTION", is to try to change the ID bit (bit 21) in
   * EFLAGS.  If it can be changed, the machine supports CPUID,
   * otherwise it doesn't.
   *
   * Some 486's, and all subsequent processors, support CPUID.
   *
   * For those who are curious, the way you distinguish between
   * an 80386 and an 80486 is to try to set the flag in EFLAGS
   * that causes unaligned accesses to fault - that's bit 18.
   * However, if the SMAP bit is set in CR4, that bit controls
   * whether explicit supervisor-mode access to user-mode pages
   * are allowed, so that should presumably only be done in a
   * very controlled environment, such as the system boot process.
   *
   * So, if you want to find out what type of CPU the system has,
   * it's probably best to ask the OS, if it supplies the result
   * of any CPU type testing it's done.
   */
  return false;
}
#else /* not x86 */

/**
 * @brief Execute a CPUID query on the current processor.
 *
 * @param CPUInfo  Output array of four 32-bit registers (EAX, EBX, ECX, EDX).
 * @param selector The CPUID leaf (function ID) to query.
 * @return true if the query was successful, false if unsupported.
 */
static bool
ws_cpuid(uint32_t *CPUInfo _U_, int selector _U_)
{
  /* Not x86, so no cpuid instruction */
  return false;
}
#endif

#else /* Other compilers */

/**
 * @brief Execute a CPUID query on the current processor.
 *
 * @param CPUInfo  Output array of four 32-bit registers (EAX, EBX, ECX, EDX).
 * @param selector The CPUID leaf (function ID) to query.
 * @return true if the query was successful, false if unsupported.
 */
static bool
ws_cpuid(uint32_t *CPUInfo _U_, int selector _U_)
{
  return false;
}
#endif

/**
 * @brief Checks if the CPU supports SSE4.2 instruction set.
 *
 * @return 1 if SSE4.2 is supported, otherwise returns 0.
 */
static int
ws_cpuid_sse42(void)
{
  uint32_t CPUInfo[4];

  if (!ws_cpuid(CPUInfo, 1))
    return 0;

  /* in ECX bit 20 toggled on */
  return (CPUInfo[2] & (1 << 20));
}

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Created: 2026-06-30 07:22