cpuid(4) [suse man page]

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

NAME

       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 3.25 of the Linux man-pages project.  A description of the project, and information about reporting bugs, can
       be found at http://www.kernel.org/doc/man-pages/.

Linux								    2009-03-31								  CPUID(4)

cpuid(7D)							      Devices								 cpuid(7D)

NAME

       cpuid - CPU identification driver

SYNOPSIS

       /dev/cpu/self/cpuid

DESCRIPTION

   SPARC and x86 system
       This  device  provides  implementation-private  information via ioctls about various aspects of the implementation to Solaris libraries and
       utilities.

   x86 systems only
       This device also provides a file-like view of the namespace and return values of the x86 cpuid instruction. The cpuid instruction  takes  a
       single  32-bit integer function code, and returns four 32-bit integer values corresponding to the input value that describe various aspects
       of the capabilities and configuration of the processor.

       The API for the character device consists of using the seek offset to set the function code value, and using a read(2) or  pread(2)  of	16
       bytes to fetch the four 32-bit return values of the instruction in the order %eax, %ebx, %ecx and %edx.

       No data can be written to the device. Like the cpuid instruction, no special privileges are required to use the device.

       The  device is useful to enable low-level configuration information to be extracted from the CPU without having to write any assembler code
       to invoke the cpuid instruction directly. It also allows the kernel to attempt to correct any erroneous data returned  by  the  instruction
       (prompted by occassional errors in the information exported by various processor implementations over the years).

       See  the  processor  manufacturers  documentation for further information about the syntax and semantics of the wide variety of information
       available from this instruction.

EXAMPLE

       This example allows you to determine if the current x86 processor supports "long mode," which is a necessary (but not sufficient) condition
       for running the 64-bit Solaris kernel on the processor.

	 /*

	 #include <sys/types.h>
	 #include <sys/stat.h>
	 #include <fcntl.h>
	 #include <unistd.h>
	 #include <string.h>
	 #include <errno.h>
	 #include <stdio.h>

	 static const char devname[] = "/dev/cpu/self/cpuid";

	 /*ARGSUSED*/
	 int
	 main(int argc, char *argv[])
	 {
		 struct {
			 uint32_t r_eax, r_ebx, r_ecx, r_edx;
		 } _r, *rp = &_r;
		 int d;
		 char *s;

		 if ((d = open(devname, O_RDONLY)) == -1) {
			 perror(devname);
			 return(1);
		 }

		 if (pread(d, rp, sizeof (*rp), 0) != sizeof (*rp)) {
			 perror(devname);
			 goto fail;
		 }

		 s = (char *)&rp->r_ebx;
		 if (strncmp(s, "Auth" "cAMD" "enti", 12) != 0 &&
		     strncmp(s, "Genu" "ntel" "ineI", 12) != 0)
			 goto fail;

		 if (pread(d, rp, sizeof (*rp), 0x80000001) == sizeof (*rp)) {
			 /*
			  * Read extended feature word; check bit 29
			  */
			 (void) close(d);
			 if ((rp->r_edx >> 29) & 1) {
				 (void) printf("processor supports long mode
");
				 return(0);
			 }
		 }
	 fail:
		 (void) close(d);
		 return(1);
	 }

ERRORS

       ENXIO	 Results from attempting to read data from the device on a system that does not support the CPU identification interfaces

       EINVAL	 Results from reading from an offset larger than UINT_MAX, or attempting to read with a size that is not multiple of 16 bytes.

FILES

       /dev/cpu/self/cpuid    Provides access to CPU identification data.

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Availability		     |SUNWckr			   |
       +-----------------------------+-----------------------------+
       |Interface Stability	     |Evolving			   |
       +-----------------------------+-----------------------------+

SEE ALSO

       psrinfo(1M), prtconf(1M), pread(2), read(2), attributes(5)

SunOS 5.11							    16 Sep 2004 							 cpuid(7D)