I was a happy user of Del.icio.us for many years until the service closed. Then I moved my links to Google Bookmarks, which offered basically the same functionality (at least for my needs): link storage with title, tags and comments. I’ve carefully tagged and filed more than 2500 links since I started, and I’ve learnt to appreciate the usefulness of searching by tag to find again some precious information that was valuable to me in the past.

As part of a summer clean-up of the desk drawers, I pulled out the N800 and N9 and ported my game Loonies 8192 to these devices. Since those are "proper" Linux devices, one can compile things directly on-device (just install gcc from the SDK repos), and with SSH, it's easy to type on a real keyboard.

Anyway, you can install the game via the landing pages:

For the N800, make sure "maemo Extras" is enabled so it will find libsdl1.2 if it's not already installed. Head over to https://loonies.thp.io/n800/ on the device and download the deb, it will be installed by Application manager.

For the N9, make sure you have n9repomirror installed (again, so libsdl1.2 can be installed if necessary). Enable third party applications in Settings, Applications, Installations. Then head over to https://loonies.thp.io/n9/ on the device and download the deb, selecting after the download is finished will ask you to install it.

The N9 version is also available on openrepos.net.

And don't forget that the game is also available for DOS, various consoles and handheld consoles as well as on Windows. All of the builds are available on itch.io.

This is the last post of the series showing interesting debugging tools, I hope you have found it useful. Don’t miss the custom scripts at the bottom to process GStreamer logs, help you highlight the interesting parts and find the root cause of difficult bugs. Here are also the previous posts of the series:

In this new post series, I’ll show you how both existing and ad-hoc tools can be helpful to find the root cause of some problems. Here are also the older posts of this series in case you find them useful:

• GStreamer WebKit debugging tricks using GDB (1/2)
• GStreamer WebKit debugging tricks using GDB (2/2)
• GStreamer WebKit debugging by instrumenting source code (1/3)
• GStreamer WebKit debugging by instrumenting source code (2/3)
• GStreamer WebKit debugging by instrumenting source code (3/3)

Use strace to know which config/library files are used by a program

If you’re becoming crazy supposing that the program should use some config and it seems to ignore it, just use strace to check what config files, libraries or other kind of files is the program actually using. Use the grep rules you need to refine the search:

$ strace -f -e trace=%file nano 2> >(grep 'nanorc')
access("/etc/nanorc", R_OK)             = 0
access("/usr/share/nano/javascript.nanorc", R_OK) = 0
access("/usr/share/nano/gentoo.nanorc", R_OK) = 0
...

Know which process is killing another one

First, try to strace -e trace=signal -p 1234 the killed process.

If that doesn’t work (eg: because it’s being killed with the uncatchable SIGKILL signal), then you can resort to modifying the kernel source code (signal.c) to log the calls to kill():

SYSCALL_DEFINE2(kill, pid_t, pid, int, sig)
{
    struct task_struct *tsk_p;
    ...
    /* Log SIGKILL */
    if (sig & 0x1F == 9) {
        tsk_p = find_task_by_vpid(pid);

        if (tsk_p) {
            printk(KERN_DEBUG "Sig: %d from pid: %d (%s) to pid: %d (%s)\n",
                sig, current->pid, current->comm, pid, tsk_p->comm);
        } else {
            printk(KERN_DEBUG "Sig: %d from pid: %d (%s) to pid: %d\n",
                sig, current->pid, current->comm, pid);
        }
    }
    ...
}

Wrap gcc/ld/make to tweak build parameters

If you ever find yourself with little time in front of a stubborn build system and, no matter what you try, you can’t get the right flags to the compiler, think about putting something (a wrapper) between the build system and the compiler. Example for g++:

#!/bin/bash
main() {
    # Build up arg[] array with all options to be passed
    # to subcommand.
    i=0
    for opt in "$@"; do
        case "$opt" in
        -O2) ;; # Removes this option
        *)
            arg[i]="$opt" # Keeps the others
            i=$((i+1))
            ;;
        esac
    done
    EXTRA_FLAGS="-O0" # Adds extra option
    echo "g++ ${EXTRA_FLAGS} ${arg[@]}" # >> /tmp/build.log # Logs the command
    /usr/bin/ccache g++ ${EXTRA_FLAGS} "${arg[@]}" # Runs the command
}
main "$@"

Make sure that the wrappers appear earlier than the real commands in your PATH.

The make wrapper can also call remake instead. Remake is fully compatible with make but has features to help debugging compilation and makefile errors.

Analyze the structure of MP4 data

The ISOBMFF Box Structure Viewer online tool allows you to upload an MP4 file and explore its structure.

This is the last post on the instrumenting source code series. I hope you to find the tricks below as useful as the previous ones.

In this post I show some more useful debugging tricks. Check also the other posts of the series:

This is the continuation of the GStreamer WebKit debugging tricks post series. In the next three posts, I’ll focus on what we can get by doing some little changes to the source code for debugging purposes (known as “instrumenting”), but before, you might want to check the previous posts of the series:

This post is a continuation of a series of blog posts about the most interesting debugging tricks I’ve found while working on GStreamer WebKit on embedded devices. These are the other posts of the series published so far:

I’ve been developing and debugging desktop and mobile applications on embedded devices over the last decade or so. The main part of this period I’ve been focused on the multimedia side of the WebKit ports using GStreamer, an area that is a mix of C (glib, GObject and GStreamer) and C++ (WebKit).

This depends on Bounce (the N900 .deb) and SDL 1.2 being installed. Google "bounce_1.0.0_armel.deb" for the former, and use n9repomirror for the latter.