[Gem5] Make a new boot image
0. Intro
I wanted to run a PARSEC 3.0 benchmark on a Gem5 full system simulator. Because the size of compiled PARSEC 3.0 benchmark was too large (about 10GB), the original full system disk image provided by Gem5 official site could not be used.
At first, I tried to mount a secondary disk image that contains benchmark files after Gem5’s full system was booted. I expected that, in this way, I could use the boot image (uploaded in the Gem5 official website) as it is mounting/unmounting several other benchmark images as my wishes.
However, unfortunately, I could not figure out the way of doing that. So, I chose the other way: making a new boot image including compiled benchmark files.
1. Problem
Require larger boot image of Gem5 full system simluator so that it can contain the benchmark files.
2. Background (Prerequisites)
2.1 Gem5
It is assumed that you have already succeeded to boot a full system of Gem5 with following command in the Gem5 root directory.
$ ./build/X86/gem5.opt configs/example/fs.py
2.2 Commands
It is recommend to learn the role of following commands.
dd
df
losetup
fdisk
mount
mke2fs
3. Solution
3.1 Make a new img file
Make a new image file with dd command. The output file will be filled with zeros. Here is an example.
$ dd if=/dev/zero of=parsec3.img bs=1M count=12288
if: input file. In this example zero.
of: output file. In this example parsec3.img.
count=12288 means total size of the output file will be 1MB * 12288 = 12GB
You can confirm that a new file has been successfully created with ls -alh command.
$ ls -alh
total 17G
drwxrwxr-x 2 yulistic yulistic 4.0K 2월 22 20:00 .
drwxrwxr-x 10 yulistic yulistic 4.0K 2월 22 18:38 ..
...
-rw-rw-r-- 1 yulistic yulistic 12G 2월 23 19:37 parsec3.img
...
3.2 Partitioning
The new image file filled with zeroes needs to be partitioned. You can use any partition programs. fdisk is used here.
First, let’s check the current status of image file.
$ fdisk -l parsec3.img
Disk parsec3.img: 12.9 GB, 12884901888 bytes
255 heads, 63 sectors/track, 1566 cylinders, total 25165824 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00000000
Disk parsec3.img doesn't contain a valid partition table
It is saying that there is no partition in the image file.
With the following command, you can get into the partition program. You might require a root privilege.
$ sudo fdisk parsec3.img
You can print help menu with option m. Option n will lead you to the process of making a new partition.
In this case, we don’t need any secondary partition. Just make one partition as a whole with default values in the progress (just hit enter!).
After the process, save the modification and escape from the program with option w.
$ sudo fdisk parsec3.img
[sudo] password for yulistic:
Device contains neither a valid DOS partition table, nor Sun, SGI or OSF disklabel
Building a new DOS disklabel with disk identifier 0x5fc418b5.
Changes will remain in memory only, until you decide to write them.
After that, of course, the previous content won't be recoverable.
Warning: invalid flag 0x0000 of partition table 4 will be corrected by w(rite)
Command (m for help): m
Command action
a toggle a bootable flag
b edit bsd disklabel
c toggle the dos compatibility flag
d delete a partition
l list known partition types
m print this menu
n add a new partition
o create a new empty DOS partition table
p print the partition table
q quit without saving changes
s create a new empty Sun disklabel
t change a partition's system id
u change display/entry units
v verify the partition table
w write table to disk and exit
x extra functionality (experts only)
Command (m for help): n
Partition type:
p primary (0 primary, 0 extended, 4 free)
e extended
Select (default p): p
Partition number (1-4, default 1): 1
First sector (2048-25165823, default 2048):
Using default value 2048
Last sector, +sectors or +size{K,M,G} (2048-25165823, default 25165823):
Using default value 25165823
Command (m for help): w
The partition table has been altered!
Syncing disks.
You can confirm that the partition has been created as below.
$ fdisk -l parsec3.img
Disk parsec3.img: 12.9 GB, 12884901888 bytes
128 heads, 33 sectors/track, 5957 cylinders, total 25165824 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x5fc418b5
Device Boot Start End Blocks Id System
parsec3.img1 2048 25165823 12581888 83 Linux
3.3 Formatting
Next, we need to format the partition. To make a virtual disk with image file, loop device will be used (losetup).
First, it is required to know the starting point of the partition. Again with the following command, you can figure out the starting position of the partition.
$ fdisk -l parsec3.img
...
Device Boot Start End Blocks Id System
parsec3.img1 2048 25165823 12581888 83 Linux
We can check that the starting position of the partition is 2048.
Second, find the available loop device.
$ sudo losetup -f
/dev/loop0
Third, create a virtual disk using loop device.
$ sudo losetup -o $((512*2048)) /dev/loop0 parsec3.img
Fourth, use mke2fs command to format the partition as ext2.
$ sudo mke2fs /dev/loop0
Last, detach loop device.
$ sudo losetup -d /dev/loop0
3.4 Copy benchmark files to the image file
Mount your image file.
$ mkdir tempdir
$ sudo mount -o loop,offset=$((2048*512)) parsec3.img tempdir
or you can use loop device as Section 3.
$ mkdir tempdir
$ sudo losetup -o $((512*2048)) /dev/loop0 parsec3.img
$ sudo mount /dev/loop0 tempdir
Copy your compiled benchmark files into the image file.
If you used loop device for mounting, you should detach loop device after use.
$ sudo losetup -d /dev/loop0
3.5 Boot the Gem5 full system simulator with the created image file
Boot with your new image and run benchmarks on Gem5 full system simulator.
$ ./build/X86/gem5.opt configs/example/fs.py --disk-image=path/to/your/imagefile/parsec3.img