flypig.co.uk

Before we get started, a content warning. If you're a little squeamish or discussions about human illness make you uncomfortable, this might be one to skip.

Because today was not the day of development I was hoping it was going to be. Last night I found myself experiencing a bad case of food poisoning. I woke in the middle of the night, or maybe I never went to sleep, feeling deeply uncomfortable. After a long period of unrest I eventually found myself arched over the toilet bowl emptying the contents of my stomach into it.

I've spent the rest of the day recuperating, mostly sleeping, consuming only liquids (large quantities of Lucozade) and drifting in and out of consciousness. It seems like it was something I ate, which means it's just a case of waiting it out, but the lack of sleep, elevated temperature and general discomfort has left me in a state of hazy semi- coherence. Focusing has not really been an option.

After having spent the day like this it's now late evening and the chance for me to do much of anything let alone development, has sadly passed.

But I'm going to try to seize the moment nonetheless. There's one simple thing I think I can do that will help my task tomorrow. You'll recall that the question I need to answer is why the following is returning a value on ESR 78, but returning null on ESR 91:

  void* widgetOpenGLContext =
      widget ? widget->GetNativeData(NS_NATIVE_OPENGL_CONTEXT) : nullptr;

The GetNativeData() method is an override, which means that there are potentially multiple different versions that might be being called when this bit of code is executed. The pointer to the method will be taken from the widget object's vtable. So it would be useful to know what method is actually being called on the two different versions of the browser.

The process for checking this is simple with the debugger: place a breakpoint on CompositorOGL::CreateContext() as before. When it hits, place a new breakpoint on every version of GetNativeData(), run the code onward and wait to see which one is hit first.

Here goes, first with ESR 78:

Thread 39 "Compositor" hit Breakpoint 1, mozilla::layers::
    CompositorOGL::CreateContext (this=0x7ea0003420)
    at gfx/layers/opengl/CompositorOGL.cpp:223
223     already_AddRefed<mozilla::gl::GLContext> CompositorOGL::CreateContext() 
    {
(gdb) b GetNativeData
Breakpoint 2 at 0x7fbbdbe5e0: GetNativeData. (5 locations)
(gdb) c
Continuing.

Thread 39 &quot;Compositor&quot; hit Breakpoint 2, mozilla::embedlite::nsWindow:
    :GetNativeData (this=0x7f80c8d500, aDataType=12)
    at mobile/sailfishos/embedshared/nsWindow.cpp:176
176       LOGT(&quot;t:%p, DataType: %i&quot;, this, aDataType);
(gdb) bt
#0  mozilla::embedlite::nsWindow::GetNativeData (this=0x7f80c8d500, 
    aDataType=12)
    at mobile/sailfishos/embedshared/nsWindow.cpp:176
#1  0x0000007fba682718 in mozilla::layers::CompositorOGL::CreateContext (
    this=0x7ea0003420)
    at gfx/layers/opengl/CompositorOGL.cpp:228
#2  0x0000007fba6a33a4 in mozilla::layers::CompositorOGL::Initialize (
    this=0x7ea0003420, out_failureReason=0x7edb30b720)
    at gfx/layers/opengl/CompositorOGL.cpp:374
#3  0x0000007fba77aff4 in mozilla::layers::CompositorBridgeParent::
    NewCompositor (this=this@entry=0x7f807596a0, aBackendHints=...)
    at gfx/layers/ipc/CompositorBridgeParent.cpp:1534
#4  0x0000007fba784660 in mozilla::layers::CompositorBridgeParent::
    InitializeLayerManager (this=this@entry=0x7f807596a0, aBackendHints=...)
    at gfx/layers/ipc/CompositorBridgeParent.cpp:1491
#5  0x0000007fba7847a8 in mozilla::layers::CompositorBridgeParent::
    AllocPLayerTransactionParent (this=this@entry=0x7f807596a0, 
    aBackendHints=..., aId=...)
    at gfx/layers/ipc/CompositorBridgeParent.cpp:1587
#6  0x0000007fbca81234 in mozilla::embedlite::EmbedLiteCompositorBridgeParent::
    AllocPLayerTransactionParent (this=0x7f807596a0, aBackendHints=..., 
    aId=...)
    at mobile/sailfishos/embedthread/EmbedLiteCompositorBridgeParent.cpp:77
#7  0x0000007fba05f3f0 in mozilla::layers::PCompositorBridgeParent::
    OnMessageReceived (this=0x7f807596a0, msg__=...) at 
    PCompositorBridgeParent.cpp:1391
[...]
#23 0x0000007fb735989c in thread_start () at ../sysdeps/unix/sysv/linux/aarch64/
    clone.S:78
(gdb)

And then with ESR 91:

Thread 37 "Compositor" hit Breakpoint 1, mozilla::layers::
    CompositorOGL::CreateContext (this=this@entry=0x7ed8002ed0)
    at gfx/layers/opengl/CompositorOGL.cpp:227
227     already_AddRefed<mozilla::gl::GLContext> CompositorOGL::CreateContext() 
    {
(gdb) b GetNativeData
Breakpoint 2 at 0x7ff41fcef8: GetNativeData. (4 locations)
(gdb) c
Continuing.

Thread 37 &quot;Compositor&quot; hit Breakpoint 2, mozilla::embedlite::nsWindow:
    :GetNativeData (this=0x7fc89ffc80, aDataType=12)
    at mobile/sailfishos/embedshared/nsWindow.cpp:164
164     {
(gdb) bt
#0  mozilla::embedlite::nsWindow::GetNativeData (this=0x7fc89ffc80, 
    aDataType=12)
    at mobile/sailfishos/embedshared/nsWindow.cpp:164
#1  0x0000007ff293aae4 in mozilla::layers::CompositorOGL::CreateContext (
    this=this@entry=0x7ed8002ed0)
    at gfx/layers/opengl/CompositorOGL.cpp:232
#2  0x0000007ff29503b8 in mozilla::layers::CompositorOGL::Initialize (
    this=0x7ed8002ed0, out_failureReason=0x7fc17a8510)
    at gfx/layers/opengl/CompositorOGL.cpp:397
#3  0x0000007ff2a66094 in mozilla::layers::CompositorBridgeParent::
    NewCompositor (this=this@entry=0x7fc8a01850, aBackendHints=...)
    at gfx/layers/ipc/CompositorBridgeParent.cpp:1493
#4  0x0000007ff2a71110 in mozilla::layers::CompositorBridgeParent::
    InitializeLayerManager (this=this@entry=0x7fc8a01850, aBackendHints=...)
    at gfx/layers/ipc/CompositorBridgeParent.cpp:1436
#5  0x0000007ff2a71240 in mozilla::layers::CompositorBridgeParent::
    AllocPLayerTransactionParent (this=this@entry=0x7fc8a01850, 
    aBackendHints=..., aId=...)
    at gfx/layers/ipc/CompositorBridgeParent.cpp:1546
#6  0x0000007ff4e07ca8 in mozilla::embedlite::EmbedLiteCompositorBridgeParent::
    AllocPLayerTransactionParent (this=0x7fc8a01850, aBackendHints=..., 
    aId=...)
    at mobile/sailfishos/embedthread/EmbedLiteCompositorBridgeParent.cpp:80
#7  0x0000007ff23fe52c in mozilla::layers::PCompositorBridgeParent::
    OnMessageReceived (this=0x7fc8a01850, msg__=...) at 
    PCompositorBridgeParent.cpp:1285
[...]
#22 0x0000007fefba889c in thread_start () at ../sysdeps/unix/sysv/linux/aarch64/
    clone.S:78
(gdb) 

So in both cases the class that the GetNativeData() method is being called from is mozilla::embedlite::nsWindow::GetNativeData. Looking at the code for this method, there's a pretty svelte switch statement inside that depends on the aDataType value being passed in. In our case this value is always NS_NATIVE_OPENGL_CONTEXT. And the code for that case is pretty simple:

    case NS_NATIVE_OPENGL_CONTEXT: {
      MOZ_ASSERT(!GetParent());
      return GetGLContext();
    }

This is the same for both ESR 78 and ESR 91, so to get to the bottom of this will require digging a bit deeper. But at least we're one step further along.

I've not made a lot of progress today, but perhaps that's to be expected. I'll continue following this lead up tomorrow.

If you'd like to read any of my other gecko diary entries, they're all available on my Gecko-dev Diary page.