Bug 47136 – WebSocket tests are crashing

• Component: WebCore Misc.
• Status: RESOLVED FIXED

[Simon Fraser (smfr)]

From Adam:


As you might have noticed, the WebSocket tests are crashing on Leopard
and Snow Leopard.  I thought for a while that this might be related to
my recent move of the WebSocket tests, but looks unrelated.  The
crashes started with a patch that flipped off the SVN executable bit
for a bunch of files, which also seems unrelated (reverting that
change locally also don't seem to make a difference).

Here's a reduced test case:

<script>
var ws = new WebSocket('ws://localhost:1111/');
</script>

Just open a local HTML file containing that code and you'll crash
WebKit on Snow Leopard (and presumably Leopard as well).  The crash
looks like some kind of heap corruption.  At this point, I'd like to
hand this off to someone who's more familiar with the WebSockets code.
Any volunteers?

[Simon Fraser (smfr)]

There's a heap corruption bug somewhere. When debugging, I see variable display of 'this' go bad in Xcode in the SocketStreamHandleBase() ctor.

Disassembling this gives:

0x0000000103c0ad64  <+0000>  push   %rbp
0x0000000103c0ad65  <+0001>  mov    %rsp,%rbp
0x0000000103c0ad68  <+0004>  mov    %rdi,-0x8(%rbp)
0x0000000103c0ad6c  <+0008>  lea    0x1437e0d(%rip),%rax        # 0x105042b80 <_ZTVN7WebCore22SocketStreamHandleBaseE>
0x0000000103c0ad73  <+0015>  lea    0x10(%rax),%rdx
0x0000000103c0ad77  <+0019>  mov    -0x8(%rbp),%rax
0x0000000103c0ad7b  <+0023>  mov    %rdx,(%rax)        <--- 'this' gets clobbered here

It's loading the vtable, but I don't know what the 
   lea    0x10(%rax),%rdx
is trying to do.

[Darin Adler]

(In reply to comment #1)
> It's loading the vtable, but I don't know what the 
>    lea    0x10(%rax),%rdx
> is trying to do.

That looks to me like a multiple-inheritance pointer adjustment. Maybe we have a problem with unsafe casting to and from "this" when there is multiple inheritance involved?

[Simon Fraser (smfr)]

The superclass certainly uses multiple inheritance:

    class SocketStreamHandle : public RefCounted<SocketStreamHandle>, public SocketStreamHandleBase, public AuthenticationClient {

but the assembly comes from the ctor of SocketStreamHandleBase, which has virtual functions, but doesn't inherit from anything.

[Simon Fraser (smfr)]

If I shuffle the inheritance order of SocketStreamHandle to:
class SocketStreamHandle : public RefCounted<SocketStreamHandle>, public AuthenticationClient, public SocketStreamHandleBase {
then things to bad in the AuthenticationClient ctor, in a similar place.

Certainly looks like an issue with multiple-inheritance pointer adjustment.

[Simon Fraser (smfr)]

The build is picking up network/qt/SocketStreamHandle.h

[Simon Fraser (smfr)]

The project was changed inadvertently in http://trac.webkit.org/changeset/68951

[Simon Fraser (smfr)]

http://trac.webkit.org/changeset/69057

[James Robinson]

FFFFFFFFUUUUUUUUUUUUUUUUUU

[Adam Barth]

Looks like we might need to trigger a world-rebuild to see this fix things on the bots.