Your posted code will work only with the microsoft compiler which is part of visual studio because it uses the microsoft specific header file intrin. Id appreciate it greatly if anybody could check over the code. In the x86 architecture, the cpuid instruction is a processor supplementary instruction allowing. Identification string in the appropriate registers. Not sure if you are confused about mov eax, 1 actually exiting, it doesnt, it just loads 1 into eax. Table 38 shows information returned, depending on the initial.
The cpuid opcode is a processor supplementary instruction its name derived from cpu identification for the x86 architecture. It was introduced by intel in 1993 when it introduced the pentium and slenhanced 486 processors a program can use the cpuid to determine processor type and whether. Our main focus is to study the basic format and usage of gcc inline assembly functions. Mostly this is realized with license files, which include the. Advancing to subleaf 1 by making another call to cpuid with eaxbh and ecx1 could for. Use of the linux msr kernel module creates a pseudofile.
To declare inline assembly functions, we use the keyword asm. Print it out to screen using the linux system call write. Before trying to rely upon cpuid, a program must properly detect and sometimes enable the instruction. 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. For the most software products the license verification is done with license keys.
The function checks if cpuid is supported and returns 1 for valid cpuid. In the x86 architecture, the cpuid instruction identified by a cpuid opcode is a processor supplementary instruction its name derived from cpu identification allowing software to discover details of the processor. The interrupt handler for int 0x80 in the operating system expects the function code in eax so thats where you should put it. In particular, the program must detect the presence of.
Using eax we can control cpuid to output different pieces of information. Assemblers and compilers will choose registers for such purposes where theres no write dependency. Why the eax segment in the packet you had in the other post is marked as cpuid. They are handy, speedy and very much useful in system programming. Using cpuid there are many ways to use cpuid, depending on where you are working. For example, it would be silly to use mov eax, eax if the instruction immediately before it were writing. When cpuid executes with eax set to 1, version information is returned in eax. It was introduced by intel in 1993 when it introduced the pentium and sl enhanced 486 processors. There is inline assembly for gcc and msvc both different, as well as using it in plain assembly files for nasm et. During my time in the it i have also seen some products, where the license is tied to the underlying hardware of your server.
This driver uses devcpucpunumcpuid, where cpunum is the minor number, and on an smp box will direct the access to cpu cpunum as listed in proccpuinfo. Returns processor identification and feature information to the eax, ebx, ecx, and edx registers, according to the input value entered initially in the eax register. The url provides like 30 different chunks of cpuid results, which of these chunks need to be converted into binary and place into cpuid. For each input value, cpuid returns 16 ascii characters using eax, ebx, ecx, and edx. Eax 1 cpuid if eax 080000004h then processor brand string supported else processor brand string not supported fi. Pada tulisan sebelumnya yang berjudul assembly di linux dengan gas, saya memperlihatkan penggunaan gnu assembler di linux. Exit code mov eax, 1 mov ebx, 0 int 80h when the above code is compiled and executed, it. How brand strings work to use the brand string method, execute cpuid with eax input of 8000002h through 80000004h. Linux and hypervisor communities incrementally define this cpuid space. The microsoft syntax seems to be better, since its not quoted into strings, you dont require the newlinetab sequence, and theres a chance the your ide could syntax highlight it. You can make use of linux system calls in your assembly programs. The code i have written, only works on linux for x86i386i686 etc.
I wanted to learn some x86 assembly code, so i wrote a tiny program which reads the cpuid feature bits found on intel cpus and outputs this to the display. Contribute to torvaldslinux development by creating an account on github. Cpuid returns processor identification and feature information in the eax, ebx, ecx, and edx registers. H ow do i find out my cpu architecture information under linux operating systems using the command line. Inline assembly is important primarily because of its ability to operate and make its output visible on c variables.
This cuts down on the output on a multiprocessor system, and is. A larger read size means multiple reads of consecutive levels. How to read cpuid instruction for each cpu on linux with. You need to take the following steps for using linux system calls in your program. Gnu assembler gas hampir tersedia di kebanyakan instalasi linux, sehingga programmer tinggal memakainya saja. The following are known processor manufacturer id strings. If sig pointer is nonnull, then first four bytes of the signature as found in ebx register are returned in location pointed by sig. You can use the proccpuinfo file or use the lscpu command to get info about cpu architecture. Cpuid4 linux programmers manual cpuid4 name top cpuid x86 cpuid access device description top cpuid provides an interface for querying information about the x86 cpu. Cpuid is an instruction used to query processor specific information. The offical check for the support of the cpuid instruction is to attempt to toggle the eflags. If you use another compiler, you must check if that provides its own support of the x86 cpuid instruction. Like all assembly languages, it uses short mnemonics to represent the fundamental instructions that the cpu in a computer can. 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 eax4.
Introduction several application notes have been written by intel to assist customers with discerning which processor their application is running on and the features supported by a particular processor. Return highest supported input value for cpuid instruction. Get cpuid this returns the cpus manufacturer id string a twelvecharacter ascii string stored in ebx, edx, ecx in that order. In general, any architectural that supports linux smp kernel, must be able to uniquely identify underlaying processor to the kernel. Ive attempted to convert the asm from 32bit to 64bit, line by line. Linux find out cpu architecture information nixcraft. Theres a tool called cpuid that one can use to query for much more detailed information than is typically present in lshw or proccpuinfo. On my fedora 19 system i was able to install the package with the following command. Its the kernel that will check value of eax after you invoke it with int 0x80. Cpuid is not specific to intel architecture, but its used in other cpus as well, for example arm mpcore, altera nios2.
Fake output of cpuid instruction information security stack. The highest basic calling parameter largest value that eax can be set to before calling cpuid is returned in eax. Output the number entered mov eax, 4 mov ebx, 1 mov ecx, num mov edx, 5 int 80h. Cpuid returns processor identification and feature information in the eax, ebx, ecx. It can have values from 0x00000000 to 0x00000001, and 0x80000000 to. Due to syntax variances of linux affinity apis with earlier kernel versions. Function returns 0 if cpuid is not supported or whatever cpuid returns in eax register. This device is accessed by lseek2 or pread2 to the appropriate cpuid level and reading in chunks of 16 bytes. Virtual cpus hypervisors set this bit to 1 and physical cpus. Bagi yang terbiasa dengan syntax intel, pada awalnya. Im trying to do this experiment which is aimed at measuring code execution times on generic linux. For example, the following pseudocode loads eax with 00h and causes cpuid to return a maximum return value and the.