How to get CPU brand information in ARM64?

Question

How to get CPU brand information in ARM64?

In Windows X86, the CPU brand can be queried with cpuid intrinsic function. Here is a sample of the code:

#include <stdio.h>
#include <intrin.h>

int main(void)
{
    int cpubrand[4 * 3];

    __cpuid(&cpubrand[0], 0x80000002);
    __cpuid(&cpubrand[4], 0x80000003);
    __cpuid(&cpubrand[8], 0x80000004);

    char str[48];
    memset(str, 0, sizeof str);
    memcpy(str, cpubrand, sizeof cpubrand);
    printf("%s\n", str);
}

What is the alternative of this in Windows ARM64?

c

windows

intrinsics

arm64

asked on Stack Overflow Mar 8, 2020 by

Biswapriyo

3 Answers

Although probably not the answer you're looking for (i.e. directly interrogating the CPU), you can fetch the "ProcessorNameString" value from the Windows Registry using code like the following:

#define BUFSIZ 64 // For easy adjustment of limits, if required

char answer[BUFSIZ] = "Error Reading CPU Name from Registry!", inBuffer[BUFSIZ] = "";
const char *csName = "HARDWARE\\DESCRIPTION\\System\\CentralProcessor\\0";
HKEY hKey;  DWORD gotType, gotSize = BUFSIZ;
if (RegOpenKeyExA(HKEY_LOCAL_MACHINE, csName, 0, KEY_READ, &hKey) == ERROR_SUCCESS) {
    if (!RegQueryValueExA(hKey, "ProcessorNameString", nullptr, &gotType, (PBYTE)(inBuffer), &gotSize)) {
        if ((gotType == REG_SZ) && strlen(inBuffer)) strcpy(answer, inBuffer);
    }
    RegCloseKey(hKey);
}

This will (or should) give you the processor's 'name' that the Windows system sees! I don't have access to an ARM64 system, so I can't properly test it but, on my x64 system, I get the following (correct) string: Intel(R) Core(TM) i7-8550U CPU @ 1.80GHz (which is exactly that returned by using __cpuid() calls to get the "Brand String").

However, like you, I would be very interested to know of a way to do this directly - i.e., how would the Windows O/S get this info on an ARM64 system?

answered on Stack Overflow Mar 8, 2020 by

Adrian Mole • edited Jul 8, 2020 by

Adrian Mole

Not a way to get name directly from the CPU either, but you can get processor name from the WMI Win32_Processor class

It can be obtained by running wmic cpu get name in cmd or (Get-WmiObject Win32_Processor).Name in PowerShell. Getting it from C# is also easy, something like

ManagementObjectSearcher mos = new ManagementObjectSearcher("SELECT Name FROM Win32_Processor")
foreach (ManagementObject mo in mos.Get())
{
    Console.WriteLine(mo["Name"]);
}

However doing that from C is a lot trickier. Luckily there's already a similar example in this answer. The main part should be like this

BSTR query    = SysAllocString(L"SELECT Name FROM Win32_Processor");
hr = services->lpVtbl->ExecQuery(services, language, query, WBEM_FLAG_BIDIRECTIONAL, NULL, &results);
...
hr = result->lpVtbl->Get(result, L"Name", 0, &name, 0, 0);
SysFreeString(query);

answered on Stack Overflow Mar 8, 2020 by

phuclv

The direct way to get this information would be to read the Main ID Register MIDR_EL1. This could be done via the mrs instruction in (inline) assembly or via the _ReadStatusReg instrinct.

Unfortunately this register cannot be accessed from user mode (i.e. EL0) and every attempt throws an exception. At Linux the behavior is then emulated so that MIDR_EL1 can still be accessed. However, I do not know or have the opportunity to test whether Windows also offers this feature.

References:

ARM64 CPU Feature Registers at kernel.org (how Linux made MIDR_EL1 accessible)
Main ID Register at developer.arm.com (from the Cortex-A53 docs)
ARM64 Instrincts at Microsoft Docs

answered on Stack Overflow Jul 8, 2020 by

fcdt

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