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cpuid(4) [linux man page]

CPUID(4)						     Linux Programmer's Manual							  CPUID(4)

cpuid - x86 CPUID access device DESCRIPTION
CPUID provides an interface for querying information about the x86 CPU. This device is accessed by lseek (2) or pread (2) to the appropriate CPUID level and reading in chunks of 16 bytes. A larger read size means multiple reads of consecutive levels. The lower 32 bits of the file position is used as the incoming %eax, and the upper 32 bits of the file position as the incoming %ecx, the latter intended for "counting" eax levels like eax=4. This driver uses /dev/cpu/CPUNUM/cpuid, where CPUNUM is the minor number, and on an SMP box will direct the access to CPU CPUNUM as listed in /proc/cpuinfo. This file is protected so that it can only be read by the user root, or members of the group root. NOTES
The CPUID instruction can be directly executed by a program using inline assembler. However this device allows convenient access to all CPUs without changing process affinity. Most of the information in cpuid is reported by the kernel in cooked form either in /proc/cpuinfo or through subdirectories in /sys/devices/system/cpu. Direct CPUID access through this device should only be used in exceptional cases. The cpuid driver is not auto-loaded. On modular kernels you might need to use the following command to load it explicitly before use: $ modprobe cpuid There is no support for CPUID functions that require additional input registers. Very old x86 CPUs don't support CPUID. SEE ALSO
Intel Corporation, Intel 64 and IA-32 Architectures Software Developer's Manual Volume 2A: Instruction Set Reference, A-M, 3-180 CPUID ref- erence. Intel Corporation, Intel Processor Identification and the CPUID Instruction, Application note 485. COLOPHON
This page is part of release 3.27 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at Linux 2009-03-31 CPUID(4)

Check Out this Related Man Page

CPUCTL(4)						   BSD Kernel Interfaces Manual 						 CPUCTL(4)

cpuctl -- cpuctl pseudo device SYNOPSIS
To compile this driver into the kernel, place the following lines in your kernel configuration file: device cpuctl Alternatively, to load the driver as a module at boot time, place the following in loader.conf(5): cpuctl_load="YES" DESCRIPTION
The special device /dev/cpuctl presents interface to the system CPU. It provides functionality to retrieve CPUID information, read/write machine specific registers (MSR) and perform CPU firmware updates. For each CPU present in the system, the special device /dev/cpuctl%d with the appropriate index will be created. For multicore CPUs such a special device will be created for each core. Currently, only i386 and amd64 processors are supported. IOCTL INTERFACE
All of the supported operations are invoked using the ioctl(2) system call. Currently, the following ioctls are defined: CPUCTL_RDMSR cpuctl_msr_args_t *args CPUCTL_WRMSR cpuctl_msr_args_t *args Read/write CPU machine specific register. The cpuctl_msr_args_t structure is defined in <sys/cpuctl.h> as: typedef struct { int msr; /* MSR to read */ uint64_t data; } cpuctl_msr_args_t; CPUCTL_MSRSBIT cpuctl_msr_args_t *args CPUCTL_MSRCBIT cpuctl_msr_args_t *args Set/clear MSR bits according to the mask given in the data field. CPUCTL_CPUID cpuctl_cpuid_args_t *args Retrieve CPUID information. Arguments are supplied in the following structure: typedef struct { int level; /* CPUID level */ uint32_t data[4]; } cpuctl_cpuid_args_t; It is equivalent to the CPUCTL_CPUID_COUNT request with level_type set to 0. CPUCTL_CPUID_COUNT cpuctl_cpuid_count_args_t *args Retrieve CPUID information. Arguments are supplied in the following structure: typedef struct { int level; /* CPUID level */ int level_type; /* CPUID level type */ uint32_t data[4]; } cpuctl_cpuid_count_args_t; The level field indicates the CPUID level to retrieve, it is loaded into the %eax register before the CPUID instruction is executed, The level_type field indicates the CPUID level type to retrieve, it is loaded into the %ecx register. The data field is used to store the received CPUID data. That is, data[0] contains the value of %eax register after the CPUID instruction is executed, data[1] is for %ebx, data[2] for %ecx, and data[3] for %edx. CPUCTL_UPDATE cpuctl_update_args_t *args Update CPU firmware (microcode). The structure is defined in <sys/cpuctl.h> as: typedef struct { void *data; size_t size; } cpuctl_update_args_t; The data field should point to the firmware image of size size. For additional information refer to cpuctl.h. RETURN VALUES
[ENXIO] The operation requested is not supported by the device (e.g., unsupported architecture or the CPU is disabled). [EINVAL] Incorrect request was supplied, or microcode image is not correct. [ENOMEM] No physical memory was available to complete the request. [EFAULT] The firmware image address points outside the process address space. FILES
/dev/cpuctl SEE ALSO
hwpmc(4), cpucontrol(8) HISTORY
The cpuctl driver first appeared in FreeBSD 7.2. AUTHORS
The cpuctl module and this manual page were written by Stanislav Sedov <>. BUGS
Yes, probably, report if any. BSD
June 20, 2014 BSD

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