ws_cpuid.h

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/*
 * 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>
 
#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__)
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__)
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 */
static bool
ws_cpuid(uint32_t *CPUInfo _U_, int selector _U_)
{
    /* Not x86, so no cpuid instruction */
    return false;
}
#endif
 
#else /* Other compilers */
 
static bool
ws_cpuid(uint32_t *CPUInfo _U_, int selector _U_)
{
    return false;
}
#endif
 
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));
}