Tribblix: manual page: cpuid.4d

CPUID(4D) Devices CPUID(4D)

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 occasional 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\n");
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