qemu interview questions
Top qemu frequently asked interview questions
I have some images of old linux distributes in flat file format, they can be used by bochs virtual machines, but I need to run them with Sun Virtual Box. Virtual Box cannot use images in this format, so I need to convert these images from flat file to .vmdk file format. Is there any way to do this?
Source: (StackOverflow)
I read on many other topics that the Android emulator starts really slow. Indeed, it takes +15 mins to start. However, on my machine is slow even after that.
The 'phone' responds with a 3-4 seconds delay and everything has a huge lag.
Is there any way to improve the performance of my laptop (Asus 1201N) is too rusty for the Android emulator?
PS: Tried in different emulator resolutions and the result is the same
Edit: My laptop has 2 cores with HyperThreading. And it shows as 4 CPU in Device Manager. However, when using the emulator, just one of the graphs is at 100%. Can I do something to make it work multi core?
Source: (StackOverflow)
I have a 2.67 GHz Celeron processor, and 1.21 GB of RAM on a x86 Windows XP Professional machine.
My understanding is that the Android Emulator should start fairly quickly on such a machine, but for me it does not. I have followed all the instructions in setting up the IDE, SDKs, JDKs and such and have had some success in starting the emulator quickly, but that is very rare. How can I, if possible, fix this problem?
Even if it starts and loads the home screen, it is very sluggish. I have tried the Eclipse IDE in version 3.5 (Galileo) and 3.4 (Ganymede).
Source: (StackOverflow)
In the Android open-source qemu code I ran across this line of code:
machine->max_cpus = machine->max_cpus ?: 1; /* Default to UP */
Is this just a confusing way of saying:
if (machine->max_cpus) {
; //do nothing
} else {
machine->max_cpus = 1;
}
If so, wouldn't it be clearer as:
if (machine->max_cpus == 0) machine->max_cpus = 1;
Interestingly, this compiles and works fine with gcc, but doesn't compile on http://www.comeaucomputing.com/tryitout/ .
Source: (StackOverflow)
For automated testing (using Hudson) I have a script that generates a bunch of emulators for many combinations of Android OS version, screen resolution, screen density and language.
This works fine, except for the language part.
I need to find a way to change the Android system locale automatically. Here's some approaches I can think of, in order of preference:
- Extracting/editing/repacking a QEMU image directly before starting the emulator
- Running some sort of system-locale-changing APK on the emulator after startup
- Changing the locale settings on the emulator filesystem after startup
- Changing the locale settings in some SQLite DB on the emulator after startup
- Running a key sequence (via the emulator's telnet interface) that would open the settings app and change the locale
- Manually starting the emulator for each platform version, changing the locale by hand in the settings, saving it and archiving the images for later deployment
Any ideas whether this can be done, either via the above methods or otherwise?
Do you know where locale settings are persisted to/read from by the system?
Solution:
Thanks to dtmilano's info about the relevant properties, and some further investigation on my part, I came up with a solution even better and simpler than all the ideas above!
I have updated his answer below with the details.
Source: (StackOverflow)
I'm learning a bit of OS development from OSDev.org. I have a kernel and I'm trying to boot in GRUB Legacy (0.97) using qemu. However, when I type kernel 200+9, I get the message
[Multiboot-elf, <0x100000:0x80:0x4008>(bad), entry=0x10000c]
This is what I expect except for the (bad) part. If I type boot now GRUB just hangs.
I think the numbers 0x100000, 0x44, 0x4008 stand for the .text segment start address, the .bss start address, and the .bss section size, respectively. I think this because running objdump -h on the kernel image gives this output:
kernel.bin: file format elf32-i386
Sections:
Idx Name Size VMA LMA File off Algn
0 .text 00000044 00100000 00100000 00001000 2**4
CONTENTS, ALLOC, LOAD, READONLY, CODE
1 .bss 00004008 00100044 00100044 00001044 2**2
ALLOC
So you can see that the numbers I mentioned almost match up. The issue is that instead of 100044, the start of .bss is just 44. And I think this is the reason why GRUB is saying bad. I can't have a section below 1 MB in memory (low memory). But objdump is telling me my sections are above that threshold, so I don't know what's wrong. Anyway, I'll paste my code below, it's relatively short. Although my question is probably very basic if you've done OS dev before, so the code might be extraneous.
;loader.s - contains the multiboot header for grub and calls the main kernel method
global loader ; making entry point visible to linker
global magic ; we will use this in kmain
global mbd ; we will use this in kmain
extern kmain ; kmain is defined in kmain.cpp
; setting up the Multiboot header - see GRUB docs for details
MODULEALIGN equ 1<<0 ; align loaded modules on page boundaries
MEMINFO equ 1<<1 ; provide memory map
FLAGS equ 0x03;MODULEALIGN | MEMINFO ; this is the Multiboot 'flag' field
MAGIC equ 0x1BADB002 ; 'magic number' lets bootloader find the header
CHECKSUM equ -(MAGIC + FLAGS) ; checksum required
section .text
loader:
align 4
dd MAGIC
dd FLAGS
dd CHECKSUM
; reserve initial kernel stack space
STACKSIZE equ 0x4000 ; that's 16k.
mov esp, stack + STACKSIZE ; set up the stack
mov [magic], eax ; Multiboot magic number
mov [mbd], ebx ; Multiboot info structure
call kmain ; call kernel proper
cli
.hang:
hlt ; halt machine should kernel return
jmp .hang
section .bss
align 4
stack: resb STACKSIZE ; reserve 16k stack on a doubleword boundary
magic: resd 1
mbd: resd 1
.
// kernel.c - Contains the main kernel method
void kmain() {
extern unsigned int magic;
if (magic != 0x2BADB002) {
// Something went wrong
}
volatile unsigned char *videoram = (unsigned char *) 0xB800;
videoram[0] = 65;
videoram[1] = 0x07;
}
Below is my custom linker script:
ENTRY (loader)
SECTIONS {
. = 0x00100000;
.text ALIGN (0x1000) : {
*(.text)
}
.rodata ALIGN (0x1000) :
{
*(.rodata*)
}
.data ALIGN (0x1000) :
{
*(.data)
}
.bss :
{
sbss = .;
*(COMMON)
*(.bss)
ebss = .;
}
/DISCARD/ : {
*(.eh_frame)
*(.comment)
}
}
And finally, I build the kernel with the following lines:
nasm -f elf -o loader.o loader.s
gcc -c -o kernel.o kernel.c
ld -T linker.ld -o kernel.bin loader.o kernel.o
cat stage1 stage2 pad kernel.bin > floppy.img
Where stage1 and stage2 are file from GRUB Legacy and pad is any 750 byte file (So stage1+stage2+pad have a file size of 102400 bytes, or 200 blocks, which is why I boot with kernel 200+9).
Finally, I run the kernel in qemu:
qemu-system-x86_64 -fda floppy.img
Source: (StackOverflow)
What book or website would you recommend to learn about QEMU? I'd like to see some usage examples as well as how to use the APIs.
Source: (StackOverflow)
I am unable to stop the emulator from command prompt gracefully.
I am using Linux Ubuntu 10.04 version (64-bit) and Android SDK Version is 2.3.
I started emulator using its snapshot. Now my concern is to shut down the running instance of Emulator gracefully. I have tried with kill -9 (process Id for emulator running) which shut downs the emulator but next time it does not start as its snapshot got corrupted. Please help me to avoid forceful shutdown of the an emulator.
Any idea how to fix it?
Source: (StackOverflow)
When passing "-curses" option to qemu, qemu displays the emulation window as default. So, how can I switch to the monitor console from the emulation window? If using graphical interface, switching between emulation window and monitor console can be achieved by "ctrl+alt+(1 or 2)". I am just not sure how to do this in the non-graphical case.
Source: (StackOverflow)
I know QEMU is used by Xen, and KVM is a fork of QEMU.
So, KVM includes that Xen adds to QEMU ? What is the name ?
Thanks
Source: (StackOverflow)
I conducted the following benchmark in qemu and qemu-kvm, with the following configuration:
CPU: AMD 4400 process dual core with svm enabled, 2G RAM
Host OS: OpenSUSE 11.3 with latest Patch, running with kde4
Guest OS: FreeDos
Emulated Memory: 256M
Network: Nil
Language: Turbo C 2.0
Benchmark Program: Count from 0000000 to 9999999. Display the counter on the screen
by direct accessing the screen memory (i.e. 0xb800:xxxx)
It only takes 6 sec when running in qemu.
But it takes 89 sec when running in qemu-kvm.
I ran the benchmark one by one, not in parallel.
I scratched my head the whole night, but still not idea why this happens. Would somebody give me some hints?
Source: (StackOverflow)
I have a program using LD_PRELOAD. The program should be run like
this, "LD_PRELOAD=/path/to/libfoo.so qemu -U LD_PRELOAD a.out", if
without gdb.
Here are what I did while running gdb.
(gdb) set environment LD_PRELOAD=/nfs_home/chenwj/tools/lib/libdbo.so
(gdb) file /nfs_home/chenwj/tools/bin/qemu-i386
(gdb) r -U LD_PRELOAD bzip2_base.i386-m32-gcc44-annotated input.source 1
But gdb gave me the error below
Starting program: /nfs_home/chenwj/tools/bin/qemu-i386 -U LD_PRELOAD bzip2_base.i386-m32-gcc44-annotated input.source 1
bash: open "/bin/bash" failed: Permission denied
During startup program exited with code 66.
Any sugguestion appreciated.
Regards, chenwj
Source: (StackOverflow)
Im trying to debug the boot sequence of a linux kernel with qemu,
the command i'm running is:
qemu -serial stdio -kernel <path to kernel> -hda <path to rootfs> -append "root=/dev/sda terminal = ttyS0"
During boot all the kernel messages are printed to the QEMU window.
Only when the boot has finished i get my prompt back to the terminal i ran QEMU in.
Now i can start using the kernel terminal I'm running and seeing the output in the terminal and not in QEMU window.
How do i get all messages including the boot messages to my terminal and not to QEMU window (because i cant scroll up in that window..) ?
Source: (StackOverflow)
I'm new to kernel development and I would like to know how to run/debug the linux kernel using QEMU and gdb. I'm actually reading Robert Love's book but unfortunately it doesn't help the reader on how to install proper tools to run or debug the kernel... So what I did was to follow this tutorial http://opensourceforu.efytimes.com/2011/02/kernel-development-debugging-using-eclipse/. I'm using eclipse as an IDE to develop on the kernel but I wanted first to get it work under QEMU/gdb. So what I did so far was:
1) To compile the kernel with:
make defconfig (then setting the CONFIG_DEBUG_INFO=y in the .config)
make -j4
2) Once the compilation is over I run Qemu using:
qemu-system-x86_64 -s -S /dev/zero -kernel /arch/x86/boot/bzImage
which launch the kernel in "stopped" state
3) Thus I have to use gdb, I try the following command:
gdb ./vmlinux
which run it correctly but... Now I don't know what to do... I know that I have to use remote debugging on the port 1234 (default port used by Qemu), using the vmlinux as the symbol table file for debugging.
So my question is: What should I do to run the kernel on Qemu, attach my debugger to it and thus, get them work together to make my life easier with kernel development.
Source: (StackOverflow)
I've to test some low level code on an ARM architecture. Typically experimentation is quite complicated on the real board, so I was thinking about QEMU.
What I'd like to get is some kind of debugging information like printfs or gdb. I know that this is simple with linux since it implements both the device driver for the QEMU Integrator and the gdb feature, but I'm not working with Linux. Also I suspect that extracting this kind of functionality from the Linux kernel source code would be complicated.
I'm searching from some simple operating system that already implements one of those features. Do you have some advice?
Thanks in advance.
Source: (StackOverflow)