Human Readable Decoding of /proc/cpuinfo for Arm Processors

One of the most common way to get CPU information is to check the content of /proc/cpuinfo. For example, this is the output I get from running the command on NanoPi NEO (Allwinner H3) board:

cat /proc/cpuinfo 
Processor	: ARMv7 Processor rev 5 (v7l)
processor	: 0
BogoMIPS	: 2400.00

processor	: 1
BogoMIPS	: 2400.00

Features	: swp half thumb fastmult vfp edsp thumbee neon vfpv3 tls vfpv4 idiva idivt 
CPU implementer	: 0x41
CPU architecture: 7
CPU variant	: 0x0
CPU part	: 0xc07
CPU revision	: 5

Hardware	: sun8i
Revision	: 0000
Serial		: 5400503583203c3c040e

cat /proc/cpuinfo

Processor : ARMv7 Processor rev 5 (v7l)

processor : 0

BogoMIPS : 2400.00

processor : 1

BogoMIPS : 2400.00

Features : swp half thumb fastmult vfp edsp thumbee neon vfpv3 tls vfpv4 idiva idivt

CPU implementer : 0x41

CPU architecture: 7

CPU variant : 0x0

CPU part : 0xc07

CPU revision : 5

Hardware : sun8i

Revision : 0000

Serial : 5400503583203c3c040e

Many fields are self-explanatory, but what about CPU implementer and CPU part numbers? Those are values stored in Arm’s CPUID Base Register, and 0x41 looks up to Arm implementer, while 0xc07 refers to Cortex A7. But I had to look it up to find out.

One solution would be to decode those values in the kernel, but the developers won’t do that probably because it may break user-space programs that rely on hexadecimal values. So instead, Riku Voipio decided to write and submit a patch for lscpu program found in util-linux package. The patch has been merged so the new ID mapping feature should be supported in util-linux 2.32 and greater.

In the meantime, I could try it out by compiling the code myself:

sudo apt install gettext autopoint bison libtool git build-essential pkg-config
git clone https://github.com/karelzak/util-linux
cd util-linux
./autogen.sh
./configure
make lscpu

sudo apt install gettext autopoint bison libtool git build-essential pkg-config

git clone https://github.com/karelzak/util-linux

cd util-linux

./autogen.sh

./configure

make lscpu

Let’s now run our freshly compiled lscpu to see if an Arm Cortex A7 processor is detected:

./lscpu
Architecture:         armv7l
Byte Order:           Little Endian
CPU(s):               4
On-line CPU(s) list:  0,1
Off-line CPU(s) list: 2,3
Thread(s) per core:   1
Core(s) per socket:   2
Socket(s):            1
Vendor ID:            ARM
Model:                5
Model name:           Cortex-A7
Stepping:             r0p5
CPU max MHz:          1200.0000
CPU min MHz:          240.0000
BogoMIPS:             9120.00
Flags:                swp half thumb fastmult vfp edsp thumbee neon vfpv3 tls vfpv4 idiva idivt

./lscpu

Architecture: armv7l

Byte Order: Little Endian

CPU(s): 4

On-line CPU(s) list: 0,1

Off-line CPU(s) list: 2,3

Thread(s) per core: 1

Core(s) per socket: 2

Socket(s): 1

Vendor ID: ARM

Model: 5

Model name: Cortex-A7

Stepping: r0p5

CPU max MHz: 1200.0000

CPU min MHz: 240.0000

BogoMIPS: 9120.00

Flags: swp half thumb fastmult vfp edsp thumbee neon vfpv3 tls vfpv4 idiva idivt

It works as ARM Cortex-A7 revision 5 is shown. It does not follow Arm’s new lower case logo / name, but who cares 🙂 We can see most of the information provided by /proc/cpuinfo and more, but the BogoMIPS number is different, and the last three lines with Hardware, Revision and Serial are not shown.

It’d be particular interesting to test it on products or boards with processors featuring custom Arm cores such as you should get values like “Qualcomm Krait” or “Marvell PJ4/PJ4b”.

Jean-Luc Aufranc (CNXSoft)

Jean-Luc started CNX Software in 2010 as a part-time endeavor, before quitting his job as a software engineering manager, and starting to write daily news, and reviews full time later in 2011.