[webkit-dev] Crash when running Linux Gdk version

Krzysztof Kowalczyk kkowalczyk at gmail.com
Tue Aug 22 19:06:38 PDT 2006

After applying linux build fixes patch () and slight modification to
FontDataGdk.cpp FontData::platformInit() to not use
cairo_scaled_font_text_extents() so that it can build against libcairo
1.0.4 I was able to build gdk version on my Ubuntu 6.05.

However, when I run gdklauncher, I immediately get a crash. I'm quite
perplexed because looking at sources this should really not happen. I
was wondering if someone hacking on gdk version also saw this problem
and knows a solution. I'm leaning towards some configuration issue
with my system.

Details of the crash:

Program received signal SIGSEGV, Segmentation fault.
QualifiedName (this=0xb78e026c, p=@0x0, l=@0x0, n=@0x0) at Shared.h:31
31      Shared.h: No such file or directory.
        in Shared.h
(gdb) bt
#0  QualifiedName (this=0xb78e026c, p=@0x0, l=@0x0, n=@0x0) at Shared.h:31
#1  0xb741e603 in WebCore::HTMLNames::init () at
#2  0xb74864fd in Frame (this=0x8078380, page=0x0, ownerElement=0x0)
at ../../page/Frame.cpp:158
#3  0xb772114a in FrameGdk (this=0x8078380, gdkdrawable=0x805fd20) at
#4  0x08048b69 in main ()
(gdb) p *this
$10 = {m_impl = 0x0}
(gdb) info reg
eax            0x0      0
ecx            0x1      1
edx            0xbfa96420       -1079417824
ebx            0xb789b0b0       -1215713104
esp            0xbfa96410       0xbfa96410
ebp            0xbfa96458       0xbfa96458
esi            0xb78e026c       -1215430036
edi            0xbfa964a0       -1079417696
eip            0xb7603ec0       0xb7603ec0 <QualifiedName+94>
eflags         0x10282  66178
cs             0x73     115
ss             0x7b     123
ds             0x7b     123
es             0x7b     123
fs             0x0      0
gs             0x33     51
(gdb) disass $eip-4 $eip+10
Dump of assembler code from 0xb7603ebc to 0xb7603eca:
0xb7603ebc <QualifiedName+90>:  mov    (%eax),%eax
0xb7603ebe <QualifiedName+92>:  mov    %eax,(%esi)
0xb7603ec0 <QualifiedName+94>:  addl   $0x1,(%eax)
0xb7603ec3 <QualifiedName+97>:  lea    0xfffffff8(%ebp),%esp
0xb7603ec6 <QualifiedName+100>: pop    %ebx
0xb7603ec7 <QualifiedName+101>: pop    %esi
0xb7603ec8 <QualifiedName+102>: pop    %ebp
0xb7603ec9 <QualifiedName+103>: ret

I speculate that this is the instruction that crashes (I can never
remember if eip points to the intstruction that generated the fault or
the one after it):
0xb7603ec0 <QualifiedName+94>:  addl   $0x1,(%eax)
because it tries to dereference memory at address 0.

It looks like it comes from     void ref() { m_impl->ref(); } which
makes sense given that according to gdb m_impl is 0x0. What doesn't
make sense is that m_impl is 0x0.

It might be because QNAME_DEFAULT_CONSTRUCTOR is defined and somehow a
default constructor got called. BTW: it seems like
QualifiedName::ref() has a bug in this case and should have the same
protection as deref() i.e.
    if (!m_impl)

All this originates from the macro in HTMLNames.cpp:
    #define INITIALIZE_TAG_GLOBAL(name) new ((void*)&name##Tag)
QualifiedName(nullAtom, name##TagString, xhtmlNS);

Which makes stepping through the code in gdb pretty much impossible
i.e. I don't see what code is actually generated by gcc.

Any hint appreciated.

-- kjk

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