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Cross Arch Remote Debugging with gdb and gdbserver

11.10.2009 at 23:31

To further debug a problem in my little initramfs system I recently added gdbserver to the build scripts. And since I have never done that before I might as well document how this works.

gdbserver which runs on the target basically just provides the 'debugging backend' and makes it available to a normal host gdb. This has the advantage that gdbserver is relatively easy to build for your embedded system of choice, it doesn't provide a user interface and therefore doesn't require readline/curses libraries.

So we cross compile gdbserver whose source can be found in the gdb tarball under gdb/gdbserver like this (replace $ARCH with your target architecture in my case it was armv4tl-unknown-linux-gnueabi):

cd gdb/gdbserver

./configure --build=`./config.guess` 
        --target=$ARCH 
        --host=$ARCH 
        --prefix=/usr 
        --program-prefix="" &&
make &&
make DESTDIR=$SOMEDIR install

Then you will need a host gdb which understands the instructions of your target architecture. Your distribution probably only enabled support for your native architecture which means you will have to build your host gdb from source. Note that this time we only set --target and build from the toplevel directory.

./configure --host=`./config.guess` 
        --build=`./config.guess` 
        --target=$ARCH &&
make &&
make DESTDIR=$SOMEDIR install

Now we can start our debugging session. On the target execute gdbserver and specify a port and your executable.

gdbserver :$SOME_PORT /path/to/file/you/want/to/debug

Back on the host connect to the listening gdbserver instance with your host gdb:

$ARCH-gdb
file /path/to/file/you/want/to/debug
target remote $IP_OF_TARGET:$SOME_PORT
set solib-absolute-prefix $ROOT_DIR
continue

The solib-absolute-prefix should point to the root directory of the target on your host. Confused? Well you probably have cross compiled all your stuff for the target and installed it into a directory on your host and this is what I mean with "the root directory of the target on your host". gdb will use the solib-absolute-prefix whenever it needs to load a shared library. What this means is that if the app you are debugging depends on a library gdb will load the library symbols from $ROOT_DIR/lib/libfoo.so instead of /lib/libfoo.so from the host system where it either has the wrong architecture or doesn't exists at all.

Hope this is useful for someone out there. At the very least I now know where to look should I have to do it again in the future when I have already forgotten how it actually works.

Marc

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Font configuration for elementary + framebuffer backend

08.10.2009 at 22:04

I found out what the problem with the elementary hello world application was. The fonts were missing. So how does font configurtion work? To answer this the XFree86 Font De-uglification HOWTO's TrueType Fonts section is useful. You basically have to copy your fonts into a directory and then run:

ttmkfdir
mkfontdir

This generates a fonts.scale file (which you can ignore because evas doesn't care about it) and a fonts.dir file which is read by evas.

The default elementary theme uses Sans as default font so we have to set up an alias for this. This can be done by creating a fonts.alias file containing for example:

Sans -misc-dejavu sans-medium-r-normal--0-0-0-0-c-0-ascii-0

However it is important that there is now trailing white space at the end of the line. Otherwise evas will reject the alias because it doesn't match with a font from the fonts.dir file which doesn't have any trailing spaces. Of course I only found this out after reading through evas source code and in the meantime I was told to just use X -- Sigh.

Anyway while reading through the source I actually noticed that evas also uses the filename without extension as a font name. So a simple symlink like:

ln -s DejaVuSans.ttf Sans.ttf

also works as alias and in this case we don't need the fonts.alias and fonts.dir files.

On a completely unrelated thing whoever came up with the idea to use XML for the fontconfig configuration files should be taken away from computers better sooner than later.

While the font problem is now solved the next thing to investigate is probably touchscreen handling which doesn't quite work the way it should.

irc

I have never been a heavy user of irc (if you are not paying attention you can just waste too much time with senseless flamewars) but sometimes it's actually a useful medium to get some answers in real time. Anyway because I haven't used my original irc nick for quite some time someone else has overtaken it's ownership. Yeah I really should add a few lines to my login scripts which authenticate my irc nick on freenode and oftc. Anyway registered some new nicks, I am now known as }mat or ]mat.

Marc

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Still just a white screen

05.10.2009 at 23:49

As I mentioned in the last blog post recent svn versions of edje require lua. The lua build by default just creates a static liblua.a I wondered what the reason for this is. And it is once again libtool related. It seems like people who actually have kind of taste don't want to use libtool. I am not yet sure whether building a shared variant is useful at all in my particular case because currently the only user is edje (for now I don't install the lua interpreter).

Posted my initial attempt at adding support for source control management systems to FWL. I don't care about the actual implementation but the functionality should be available in one way or another.

Unfortunately my elementary test application still just shows a completely white screen. Ran the whole thing under strace to check whether it tries to open some thing which isn't there, but saw nothing suspicious so far. Played a bit with fbset and /etc/fb.modes but no look. Need to ping the enlightenment folks and finally post an RFC about the whole thing to the openmoko-devel list.

Marc

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More automake and libtool mystery

01.10.2009 at 11:02

Initially I based my bootmenu system around the EFL Snapshots from Juli 29th. The idea was to start with some known to work state instead of a randomly picked svn revision. Once I had everything compiled I wanted to run the elementary hello world application. Unfortunately all I got was a completely white screen. But hey it didn't segfault which is progress.

I then decided to update to a more recent svn revision to see whether it was an upstream error which got fixed in the meantime or if it was an error on my side. I choose the same revision as the OpenWRT folks. Again with the idea that it had worked for others before. Because I was now checking out upstream sources I needed to run aclocal, auto{header,conf,make} and libtoolize to generate the actual Makefiles etc. Unfortunately this didn't quite work out for me because apperently automake-1.11 does't like trailing slashes. This just shows how fragile the whole autohell system actually is.

I then decided to update to current svn HEAD because the latest and greatest should have all the bugs fixed, right? By the way this added lua as dependency. Unfortunately this resulted in build errors whenever a library package had it's library compiled and wanted to link against it later during the build. For some yet unknown reason libtool wasn't linking the binaries against the required libraries. After some head scratching I compared the libtool script as shipped with the EFL snapshots from Juli and the one generated by me locally. The crucial difference was the following line:

# Whether libtool must link a program against all its dependency libraries.
link_all_deplibs=no

Don't know yet why it was set to no in the first place but I decided to go with the quick and dirty solution for now and added a sed one liner to set the variable value to unknown after the ./configure stage. The build succeeded, Yay!

With this whole thing I wasted another few hours and unfortunately the end result was the same (the elementary hello world application just showed a white screen).

On the upside I am now on the bleeding edge enlightenment stuff which was the only sane thing to do in the long run anyway.

Marc

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Cross compiling revival

28.09.2009 at 19:33

While the idea of avoiding cross compilation is certainly desirable it's currently not really feasible performance wise for my poor little macbook. I therefore adjusted my scripts to support cross compilation. That means additional pain but once it works it should be relatively fast.

libtool madness

Of course I ran into some common cross compiling pitfalls were some part of the build tries to pull in various bits from the host system. In my particular case it was libtool that had some wrong paths in it's *.la files which then tried to link against libraries from the host system which obviously is doomed to fail. Of course I spent considerable time reading through configure and finally libtool shell scripts before finding out what was going on. The lesson here is probably: always ask Google if the problem isn't solved within 5-10 minutes. However what gave me the rest was the number one motivation / design goal of libtool which is:

The system must be as elegant as possible.

Epic fail!

pkg-config sysroot support

A similar problem exists with pkg-config which also has some paths in it's *.pc files. In the latest release (0.23) there is support for a PKG_CONFIG_SYSROOT_DIR environment variable which will prefix any -L -I compiler options with the specified value. Unfortunately for some reason Debian unstable which I have installed on my macbook is still stuck with version 0.22 albeit 0.23 was released back in January 2008. I'm wondering what's the reason for this delay. Anyway I have added a workaround for the problem in my build scripts.

boot distro status

I so far have cross compiled all the necessary dependencies of elementary but for some reason an elementary hello world app doesn't yet work.

Back to debugging.

Marc

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