Steve Kemp's Blog Writings relating to Debian & Free Software

Failing to debug a crash with epiphany-browser and webkit

Monday, 20 August 2012

Today I'm in bed, because I have le sniffles, and a painful headache. I'm using epiphany to write this post, via VNC to my main desktop, but I'm hating it as I've somehow evolved into a state where the following crashes my browser:

  • Open browser.
  • Navigate to gmail.com
  • Login.
  • Wait for page to complete loading, showing my empty inbox.
  • Click "signout".

Running under GDB shows nothing terribly helpful:

Program received signal SIGSEGV, Segmentation fault.
0x0000000000000000 in ?? ()
(gdb) bt
#0  0x0000000000000000 in ?? ()
#1  0x00007ffff51a0a46 in ?? () from /usr/lib/libwebkit-1.0.so.2
#2  0x00007ffff3d8f79d in ?? () from /usr/lib/libsoup-2.4.so.1
#3  0x00007ffff2a4947e in g_closure_invoke () from /usr/lib/libgobject-2.0.so.0
#4  0x00007ffff2a5f7f4 in ?? () from /usr/lib/libgobject-2.0.so.0
...

To get more detail I ran "apt-get install epiphany-browser-dbg" - this narrows down the crash, but not in a useful way:

Program received signal SIGSEGV, Segmentation fault.
0x0000000000000000 in ?? ()
(gdb) bt
#0  0x0000000000000000 in ?? ()
#1  0x00007ffff51a0a46 in finishedCallback (session=<value optimized out>, msg=0x7fffd801d9c0, data=) at ../WebCore/platform/network/soup/ResourceHandleSoup.cpp:329
#2  0x00007ffff3d8f79d in ?? () from /usr/lib/libsoup-2.4.so.1
#3  0x00007ffff2a4947e in g_closure_invoke () from /usr/lib/libgobject-2.0.so.0
#4  0x00007ffff2a5f7f4 in ?? () from /usr/lib/libgobject-2.0.so.0
..

So this crash happens in ResourceHandleSoup.cpp. Slowly I realized that this came from the webkit package.

We see that the last call by name is to the function in line ResourceHandleSoup.cpp:329, that puts us at the last line of this function:

// Called at the end of the message, with all the necessary about the last informations.
// Doesn't get called for redirects.
static void finishedCallback(SoupSession *session, SoupMessage* msg, gpointer data)
{
    RefPtr<ResourceHandle> handle = adoptRef(static_cast<ResourceHandle*>(data));

    // TODO: maybe we should run this code even if there's no client?
    if (!handle)
        return;

    ResourceHandleInternal* d = handle->getInternal();

    ResourceHandleClient* client = handle->client();
    if (!client)
       return;

..
..
    client->didFinishLoading(handle.get());
}

So we see there is some validation that happens, then a call to "didFinishLoading" and somewhere shortly after that it dies. didFinishLoading looks trivial:

void WebCoreSynchronousLoader::didFinishLoading(ResourceHandle*)
{
      g_main_loop_quit(m_mainLoop);
      m_finished = true;
}

So my mental-debugging is stymied. I blame my headache. It looks like there is no obvious NULL-pointer deference, if we pretend client cannot be NULL. So the next step is to get the source, the build-dependencies and then build a debug version of webkit. I ran "apt-get source webkit", then editted the file ./debian/rules to add --enable-debug and rebuilt it:

skx@precious:~/Debian/epiphany/webkit-1.2.7$ DEB_BUILD_OPTIONS="nostrip noopt" debuild -sa

*time passes*

The build fails:

  CXX    WebCore/svg/libwebkit_1_0_la-SVGUseElement.lo
../WebCore/svg/SVGUseElement.cpp: In member function ‘virtual void WebCore::SVGUseElement::insertedIntoDocument()’:
../WebCore/svg/SVGUseElement.cpp:125: error: ‘class WebCore::Document’ has no member named ‘isXHTMLDocument’
../WebCore/svg/SVGUseElement.cpp:125: error: ‘class WebCore::Document’ has no member named ‘parser’
make[2]: *** [WebCore/svg/libwebkit_1_0_la-SVGUseElement.lo] Error 1

Ugh. So I guess we disable that "--enable-debug", and hope that "nostrip noopt" helps instead.

*Thorin sits down and starts singing about gold*

Finally the debugging build has finished and I've woken up again. Let us do this thing. I'd looked over the webkit tracker and the crashing bugs list in the meantime, but nothing jumped out at me as being similar to my issue.

Anyway without the --enable-debug flag present in the call to ../configure the Debian webkit packages were built, eventually, and installed:

skx@precious:~/Debian/epiphany$ mv libwebkit-dev_1.2.7-0+squeeze2_amd64.deb x.deb
skx@precious:~/Debian/epiphany$ sudo dpkg --install libweb*deb
[sudo] password for skx:
(Reading database ... 173767 files and directories currently installed.)
Preparing to replace libwebkit-1.0-2 1.2.7-0+squeeze2 (using libwebkit-1.0-2_1.2.7-0+squeeze2_amd64.deb) ...
Unpacking replacement libwebkit-1.0-2 ...
Preparing to replace libwebkit-1.0-2-dbg 1.2.7-0+squeeze2 (using libwebkit-1.0-2-dbg_1.2.7-0+squeeze2_amd64.deb) ...
Unpacking replacement libwebkit-1.0-2-dbg ...
Preparing to replace libwebkit-1.0-common 1.2.7-0+squeeze2 (using libwebkit-1.0-common_1.2.7-0+squeeze2_all.deb) ...
Unpacking replacement libwebkit-1.0-common ...
Setting up libwebkit-1.0-common (1.2.7-0+squeeze2) ...
Setting up libwebkit-1.0-2 (1.2.7-0+squeeze2) ...
Setting up libwebkit-1.0-2-dbg (1.2.7-0+squeeze2) ...
skx@precious:~/Debian/epiphany$

Good news everybody: The crash still happens!

Firing up GDB should hopefully reveal more details - but sadly it didn't.

Program received signal SIGSEGV, Segmentation fault.
0x0000000000000000 in ?? ()
(gdb) bt
#0  0x0000000000000000 in ?? ()
#1  0x00007ffff51a0a46 in finishedCallback (session=, msg=0xb03420, data=) at ../WebCore/platform/network/soup/ResourceHandleSoup.cpp:329
..
(gdb) up
#1  0x00007ffff51a0a46 in finishedCallback (session=, msg=0xb03420, data=) at ../WebCore/platform/network/soup/ResourceHandleSoup.cpp:329
329     client->didFinishLoading(handle.get());
(gdb) p client
$1 = <value optimized out>

At this point my head hurts too much, and I'm stuck. No quote today, I cannot be bothered.

| No comments

 

 

Spiral Logo

Search

Recent Posts

Recent Tags

Links

RSS Feed

  • Subscribe to feed