[Development] QJsonPrivate::Parser::parseObject broken on big endian

[Konstantin Tokarev]

03.09.2012, 15:21, "Olivier Goffart" <olivier at woboq.com>:

>  On Sunday 02 September 2012 23:10:18 Konstantin Tokarev wrote:
>>   Hi all,
>>
>>   When building Qt 5 on big endian host (PPC) I've found moc breaking on Qt
>>   classes containing Q_PLUGIN_METADATA with
>>
>>   ASSERT: "idx >= 0 && idx < s" in file
>>   ../../../include/QtCore/../../src/corelib/tools/qvarlengtharray.h, line 111
>>
>>   It turned out to be a fault of QJsonPrivate::Parser::parseObject which has
>>   different code for handling of big endian and little endian cases:
>>
>>       if (parsedObject.offsets.size()) {
>>           int tableSize = parsedObject.offsets.size()*sizeof(uint);
>                                                       ^^^^^^^^^^^^^
>
>  The error is there:  one should multiply tableSize by sizeof(uint) only if one
>  do a memcpy.
>>           table = reserveSpace(tableSize);
>>   #if Q_BYTE_ORDER == Q_LITTLE_ENDIAN
>>           memcpy(data + table, parsedObject.offsets.constData(), tableSize);
>>   #else
>>           offset *o = (offset *)(data + table);
>>           for (int i = 0; i < tableSize; ++i)
>>               o[i] = parsedObject.offsets[i];
>>
>>   #endif
>>       }
>>
>>   Could anyone explain why memcpy cannot be used for big endian case here?
>  I guess that's because the offsets needs to be stored in little endian.
>  offset is a typedef to a class that has an assignement operator which swap the
>  bytes.

It turned out to be not the only place where memcpy is working incorrectly.
Unit test segfaults on memcpy in Value::copyData 

404     case QJsonValue::Array:
405     case QJsonValue::Object: {
406         const QJsonPrivate::Base *b = v.base;
407         if (!b)
408             b = (v.t == QJsonValue::Array ? &emptyArray : &emptyObject);
409         memcpy(dest, b, b->size);
410         break;
411     }

I tried to understand why memcpy fails here and how to replace it for BE case,
but still don't have a clue. I'm also quite disappointed to see so heavily endian-
dependent code written nowadays.

-- 
Regards,
Konstantin