Bug 117312 – Encode CallFrame::Location flags in the low bits when USE(JSVALUE32_64).

• Component: JavaScriptCore
• Status: RESOLVED FIXED

[Michael Saboff]

ASSERT(hasLocationAsBytecodeOffset()) is called in CallFrame::locationAsBytecodeOffset() and CallFrame::setLocationAsBytecodeOffset() for JSVALUE32_64 builds. The 32 bit value stored in ArgumentCount tag for the JSVALUE32_64 builds is a pointer which may have the high bit set.  This high bit is used to determine whether hasLocationAsBytecodeOffset() or hasLocationAsCodeOriginIndex() is true.  Therefore these checks are meaningless to 32 bit builds.

I believe that some of the work in https://bugs.webkit.org/show_bug.cgi?id=117262 needs to be changed for 32 bit builds.

[Mark Lam]

(In reply to comment #0)
> ASSERT(hasLocationAsBytecodeOffset()) is called in CallFrame::locationAsBytecodeOffset() and CallFrame::setLocationAsBytecodeOffset() for JSVALUE32_64 builds. The 32 bit value stored in ArgumentCount tag for the JSVALUE32_64 builds is a pointer which may have the high bit set.  This high bit is used to determine whether hasLocationAsBytecodeOffset() or hasLocationAsCodeOriginIndex() is true.  Therefore these checks are meaningless to 32 bit builds.
> 
> I believe that some of the work in https://bugs.webkit.org/show_bug.cgi?id=117262 needs to be changed for 32 bit builds.

Yes, ideally, we should fix the 64 bit port so that its offset is in units of bytes instead of int64_t's.  That will allow us to use the low 2 bits for flags.

[Mark Lam]

Actually, I can implement a quick fix for this using the patch I'll land for https://bugs.webkit.org/show_bug.cgi?id=117209.

[Mark Lam]

Created attachment 203966 [details]
the patch.

[Michael Saboff]

Comment on attachment 203966 [details]
the patch.

View in context: https://bugs.webkit.org/attachment.cgi?id=203966&action=review

r=me

> Source/JavaScriptCore/ChangeLog:7
> +

Add some text saying that we are using the low 2 bits and the reason is that the upper bits are needed for addresses.

[Mark Lam]

Thanks for the review.  Landed in r151291: <http://trac.webkit.org/changeset/151291>.