Bug 118242 – Fix cast-align warnings in JavaScriptCore/heap/HandleBlockInlines.h

• Component: JavaScriptCore
• Status: RESOLVED FIXED

[Csaba Osztrogonác]

/home/oszi/Source/JavaScriptCore/heap/HandleBlockInlines.h:58:51: warning: cast from 'char*' to 'JSC::HandleNode*' increases required alignment of target type [-Wcast-align]

This code introduced in http://trac.webkit.org/changeset/146734 :

...
inline char* HandleBlock::payload()
{
    return reinterpret_cast<char*>(this) + WTF::roundUpToMultipleOf<sizeof(double)>(sizeof(HandleBlock));
}

inline HandleNode* HandleBlock::nodes()
{
    return reinterpret_cast<HandleNode*>(payload());    <------ line 58
}
...

This part of JSC isn't quite clear for me. As far as I understand a 
HandleBlock is 4K sized block on JSC heap, which contains HandleNode 
instances on int payload. And the payload is 64 bit aligned after
the HandleBlock instance. Am I correct?

If yes, I think this casting is safe and can be supressed by using
reinterpret_cast_ptr instead of reinterpret_cast, because HandleNode
has two following members: JSValue, HandleNode* and HandleNode* .

[Csaba Osztrogonác]

Created attachment 205807 [details]
Patch

[Mark Hahnenberg]

Comment on attachment 205807 [details]
Patch

r=me. We use char* to make the pointer arithmetic easier, so it's fine that the cast changes the alignment. Thanks for fixing this!

[Csaba Osztrogonác]

Comment on attachment 205807 [details]
Patch

Clearing flags on attachment: 205807

Committed r152225: <http://trac.webkit.org/changeset/152225>

[Csaba Osztrogonác]

All reviewed patches have been landed.  Closing bug.