[Interest] ASSERT / Debug Crash in Qt 5.3.2. WTF, Windows x64, LLIntData.cpp at bitwise_cast<uint32_t*>(&testVector)[sizeof(void*)/sizeof(uint32_t) + 1] == 42)

[Andre Barth]

Hi Allan,

Thanks for the prompt response. I will go ahead & log a bug.

FWIW - Below is some test output.

Thanks,
Andre

//some changed test code:
Vector<int> testVector;
testVector.resize(42);

auto sizeOfCalc = (sizeof(void*)/sizeof(uint32_t) + 1);

auto address  = &testVector;
auto castResult = bitwise_cast<uint32_t*>(&testVector);
auto indexedResult = castResult[sizeOfCalc];

bool result = (indexedResult == 42);

//and the corresponding "online" checks & results...

sizeof(void*)
0x0000000000000008

sizeof(uint32_t)
0x0000000000000004

sizeOfCalc
0x0000000000000003

address
0x00000000002ce7d8 {m_size=0x0000002a }
    WTF::VectorBuffer<int,0>: {...}
    m_size: 0x0000002a

castResult
0x00000000002ce7d8 {0x083f8450}

indexedResult
0xcccccccc

castResult[0]
0x083f8450

castResult[1]
0x00000000

castResult[2]
0x0000002a


-----Original Message-----
From: Allan Sandfeld Jensen [mailto:carewolf at gmail.com] On Behalf Of Allan Sandfeld Jensen
Sent: Friday, October 10, 2014 3:09 PM
To: interest at qt-project.org
Cc: Andre Barth
Subject: Re: [Interest] ASSERT / Debug Crash in Qt 5.3.2. WTF, Windows x64, LLIntData.cpp at bitwise_cast<uint32_t*>(&testVector)[sizeof(void*)/sizeof(uint32_t) + 1] == 42)

On Friday 10 October 2014, Andre Barth wrote:
> Hi all,
> 
> I built a JIT-free version of Qt 5.3.2 (Win64) and now run into this 
> assertion in
> 
> ..\Qt\qtwebkit\Source\JavaScriptCore\llint\LLIntData.cpp
> 
> Vector<int> testVector;
> testVector.resize(42);
> ASSERT(bitwise_cast<uint32_t*>(&testVector)[sizeof(void*)/sizeof(uint3
> 2_t)+
>  1] == 42);
> 
> Here is a bug report / changeset I've found wrt this:
> 
> http://trac.webkit.org/changeset/148896/trunk/Source/JavaScriptCore/ll
> int/L
> LIntData.cpp
> 
> and
> 
> https://bugs.webkit.org/show_bug.cgi?id=97268
> 
> The assert is supposed to check, that the Vector's m_size variable is 
> at the correct address, I guess?!
> 
> If not, anyone can shed a light on this and explain the purpose of it 
> and where I might have incorrect compilation settings applied?
> 
> Am I missing somewhere an alignment pragma or something to make this
> (sizeof(void*)/sizeof(uint32_t))
> always calculate the right address - regardless of whether its x86 or x64?
> 
There are some differences between alignment and exact types between linux x64 and win x64. Could you test what (sizeof(void*)/sizeof(uint32_t)) is, and what is on the first few ints of the address of Vector<int> after a resize(42)?

Anyway, it might we worth opening a bug for to track the issue. Even if the assert turns out to be harmless, the binaries should be able to run in debug versions (even win64).

`Allan