[debug] getting valgrind full backtrace when debugging a dynamically loaded library

Little tip:

If you are getting something like this in valgrind while debugging a dynamically loaded library, it is because the symbols from the library have been deleted when the program called dl_close.


==23759==
==23759== HEAP SUMMARY:
==23759== in use at exit: 39,684 bytes in 23 blocks
==23759== total heap usage: 2,433 allocs, 2,410 frees, 6,965,904 bytes allocated
==23759==
==23759== 24 bytes in 1 blocks are definitely lost in loss record 4 of 15
==23759== at 0x402C1BC: malloc (vg_replace_malloc.c:299)
==23759== by 0x4873C87: ???
==23759== by 0x4873DD7: ???
==23759== by 0x48662E5: ???
==23759== by 0x4866324: ???
==23759== by 0x486625D: ???
==23759== by 0x485F5A8: ???
==23759== by 0x485CC73: ???
==23759== by 0x485BCF5: ???
==23759== by 0x804BCE3: setPortParameters() (main.cpp:147)
==23759== by 0x805070D: safeMain(int, char**) (main.cpp:588)
==23759== by 0x8051E8A: main (main.cpp:661)


You need to remove the dl_close call to get a full stack trace.

[Kernel] Initramfs is too big ...

Kernel is not booting...

You then realize that your initramfs is very big : 200MB ...

A normal initramfs can range between 2MB to ~20MB in general.
If your initramfs is too big, then the kernel will not be able to map it in memory and it won't boot.

You can remove all the things your computer won't use anyway from the bloated initramfs.

Edit /etc/initramfs-tools/initramfs.conf
and set MODULES=dep instead of MODULES=most

You can then rebuild your kernel.

Sources

http://askubuntu.com/questions/299396/how-to-reduce-the-size-of-initrd-img-on-ubuntu-13-04

[cmdline] MoreUtils

The errno util

Just a quick note to praise the moreutils package.

When programming userspace application that communicate with drivers, you will always get some errno number or somme perror formated strings.

errno is just the tool that make it easy to get the information about the error.

$ errno 12
ENOMEM 12 Cannot allocate memory


$ errno -s memory
ENOMEM 12 Cannot allocate memory
EHWPOISON 133 Memory page has hardware error


You don't need this site anymore.

Source:

https://joeyh.name/code/moreutils/

[android] Building the android kernel for the x86_64 emulator

See previous post for more details: Here

my avd is Nexus_5_API_22

export my_avd=Nexus_5_API_22

What is the version of linux running on the x86_64 emulator ?

adb shell dmesg| grep "Linux version"

<5>[    0.000000] Linux version 3.10.0+ (tic@debian) (gcc version 4.9.2 (Debian 4.9.2-10) ) #2 PREEMPT Fri Jun 5 15:07:50 CEST 2015

Oh it's a more recent one than the i386 version!

git checkout remotes/origin/android-goldfish-3.10 -b emu_x86_64
ls arch/x86/configs
i386_defconfig      i386_ranchu_defconfig  x86_64_emu_defconfig
i386_emu_defconfig  x86_64_defconfig       x86_64_ranchu_defconfig

There are more config than before, great it means it is actively developped :)

Ranchu is the successor of goldfish, based on a more resent version of qemu. Linaro team is working on it, It should replace Goldfish in due time. (It even support the android arm64 platform :) )

But for now the emulator which ships with android is goldfish so let's stay with that.

ARCH=x86_64
make x86_64_emu_defconfig
make -j`nproc`

Give it a try:

emulator -kernel arch/x86/bzImage -avd $my_avd -qemu -enable-kvm

I couldn't get it to work with this exact commandline, so I used

emulator64-x86 -kernel arch/x86/boot/bzImage -avd $my_avd -gpu off -qemu --enable-kvm 

That's all! Now developp you own modules ;)

[android] Building the android kernel for the i386 emulator

To build for x86-64, check this article:
http://tic-le-polard.blogspot.fr/2015/06/android-building-android-kernel-for_6.html

Get the goldfish kernel.

git clone https://android.googlesource.com/kernel/goldfish

The master branch is empty, you need to find a commit where arch/x86/configs/goldfish_defconfig exist because the CONFIG options you need to build the kernel correctly for the emulation platform are in it.
Let's list all the different branch of the kernel

git branch -a 
 
  master
  remotes/origin/HEAD -> origin/master
  remotes/origin/android-3.10
  remotes/origin/android-3.4
  remotes/origin/android-goldfish-2.6.29
  remotes/origin/android-goldfish-3.10
  remotes/origin/android-goldfish-3.4
  remotes/origin/linux-goldfish-3.0-wip
  remotes/origin/master

Now check what version of the kernel the emulator is running:
Follow the android guide to get android studio : http://developer.android.com/tools/studio/index.html

Create a hello world app and run it in the emulator and create an x86 avd.
(You can also directly use the sdk tools to create them, but here everything is pretty much automated and the configuration is done for you.)

Use adb to connect to the emulator.
Add to your path the platform-tools and tools directory from the sdk directory.

adb devices # list all emulator instances
adb shell dmesg| grep "Linux version"

<5>[    0.000000] Linux version 3.4.67+ (digit@tyrion.par.corp.google.com) (gcc version 4.8 (GCC) ) #3 PREEMPT Tue Sep 16 19:46:22 CEST 2014

Let's get the 3.4 version of the goldfish kernel. It is proved to work :)

git checkout remotes/origin/android-goldfish-3.4 -b emu_x86

ls arch/x86/configs
goldfish_defconfig  i386_defconfig  x86_64_defconfig

Yeah, there is a goldfish config

export ARCH=x86
make goldfish_defconfig
make -j`nproc`

That's it you should have a working kernel for the emulator to test it:

emulator -list-avds
emulator -kernel arch/x86/bzImage -avd $your_avd -qemu -enable-kvm

You are now using your own kernel, you can compile your own modules for it, etc.

[qemu] Spice your qemu up

Spice is a free and open-source alternative to the VNC protocol. It is actually faster and safer. It enables you to use a remote viewer on your application.

In the host:

apt-get install virt-viewer

This will install remote-viewer, don't use spicec as it is deprecated.

In the guest VM:

apt-get install spice-vdagent

Now let's boot our VM using spice for the display.

qemu-system-x86_64 -drive file=debian_bootstrap2.qcow2,cache=none,if=virtio \ 
--enable-kvm \ 
-net nic,model=virtio,macaddr=52:54:00:12:34:58 \ 
-net vde,sock=/tmp/switch1.ctl -cpu host \ 
-smp 4 -m 2G \ 
-vga qxl -spice port=5900,addr=127.0.0.1,disable-ticketing \ 
-device virtio-serial-pci \ 
-device virtserialport,chardev=spicechannel0,name=com.redhat.spice.0 \ 
-chardev spicevmc,id=spicechannel0,name=vdagent

There is a lot to process here. all the options before the -vga are my usual options, enabling the net via vde (see my post on this here) and enabling virtio for everything.

The -smp 4 option tell kvm to use 4 cores on my computer.

I use -cpu host because I don't want some feature to disappear in the emulation, also It might be faster.

The -vga qxl is the recommanded vga for use with the spice protocol.

The -spice gives the Qemu integrated spice server its configuration. Here we specify the port and the adress of the server. As this is a local setup, we don't need a certified connection, so I disabled the ticketing.

If your VM is on your server, you might want to reconsider this choice as anyone can hijack the connection if you are not careful. Hackers are hardcore people, they are waiting for you in the internet, wearing ski masks and typing in the most awkward position. So encrypt your communications if you don't want to be a victim of these kind of people.






I will describe the use of spice with certificates in another article as you need to set up a CA to get it working.

With these options, you can already use the spice procol to get your virtual machine exported display. In fact you don't need to install the spice-vdagent for that.

But you can get more: copy and paste between the host and the vm and automatic resizing of X.

The -device virtio-serial-pci is the bus where all the virtserialport are plugged, so you need it to declare the use of a virtserialport device.

The -device virtserialport,chardev=spicechannel0,name=com.redhat.spice.0 is the actual port plugged in the virtio serial bus. its name enable the guest agent to connect to it.

The -chardev spicevmc,id=spicechannel0,name=vdagent is the character device to which the spice client will connect to communicate with guest agent using the virtio serial bus.

Now you can connect to your VM using:

remote-viever spice://127.0.0.1:5900

Have fun :)

Links

http://www.linux-kvm.org/page/SPICE
https://wiki.archlinux.org/index.php/QEMU#Spice_support

[System] Patching an initramfs

Extract the cpio filesystem in a directory, create or modify files, recreate a new cpio archive.

CPIO_FILE="rootfs.cpio"
CPIO_DIR="/tmp/yourCpioDir"
#Extract the cpio archive in the CPIO_DIR
mkdir $CPIO_DIR
pushd $CPIO_DIR
fakeroot cpio -i < $CPIO_FILE
#Apply your changes
#Recreate the cpio archive
find . | cpio --create --format='newc' > $CPIO_FILE