[webkit-dev] Question about JavaScriptCore's JSEvaluateScript function.

[Zoltan Herczeg]

Why do you want to use the original context pointer? The context is
something like "current machine state". It is important for JS function
return, exception handling, and many other things. It is not a global
pointer, like JSGlobalData (JSContextGroupRef), it points to the current
context.

Zoltan

> Thanks for your answer. Then, in the callback function (such as
> GetPropertyCallback), is it ok to use the original context pointer created
> at beginning? Or the ctx passed to the callback must be used instead?
>
> Regards
> James Su
>
> On Mon, Mar 2, 2009 at 4:52 PM, Zoltan Herczeg
> <zherczeg at inf.u-szeged.hu>wrote:
>
>> Hi,
>>
>> that is intended, since the context pointer is the current
>> CallFrame/ExecState. WebKit creates its own stack (called RegisterFile)
>> to
>> run JavaScript. The stack base of the current function is pointed by
>> CallFrame (similar to ebp in x86, or fp in ARM architectures). When you
>> call a JS function, several important pointers are stored on the top of
>> the stack, like return value, current code block, previous call frame,
>> and
>> these values are accessed through the CallFrame pointer. It is essential
>> for JavaScriptCore, there is no workaround.
>>
>> Zoltan
>>
>> > Hi,
>> >   Recently, I'm writing an application which uses JavaScriptCore to
>> > execute
>> > javascript code. I just encountered a problem when using
>> JSEvaluateScript
>> > function to evaluate a piece of script. When executing the script,
>> some
>> > callbacks provided by my code will be called, but I found that the
>> context
>> > received by callbacks are different than the context I created and
>> passed
>> > to
>> > JSEvaluateScript function.
>> >
>> > Attached is a test program.
>> > Below is the output of this program on my system (ubuntu 8.04 64bit
>> with
>> > latest webkit svn):
>> >
>> > Create context 0x7faf5d567e88, global object 0x7faf5d530000
>> > InitializeCallback(ctx=0x7faf5d567e88, obj=0x7faf5d532400)
>> > HasPropertyCallback(ctx=0x7faf50c4b048, obj=0x7faf5d532400,
>> > prop=prototype)
>> > CallAsConstructorCallback(ctx=0x7faf50c4b0c0, obj=0x7faf5d532400)
>> > InitializeCallback(ctx=0x7faf50c4b0c0, obj=0x7faf5d532440)
>> > SetPropertyCallback(ctx=0x7faf50c4b048, obj=0x7faf5d532440,
>> prop=prop1)
>> > HasPropertyCallback(ctx=0x7faf50c4b048, obj=0x7faf5d532440,
>> prop=prop1)
>> > FinalizeCallback(obj=0x7faf5d532400)
>> > FinalizeCallback(obj=0x7faf5d532440)
>> >
>> > You can see that, the callback functions received several different
>> > context
>> > pointers comparing to the one created at first beginning.
>> >
>> > Is it an intend behavior or a bug of webkit? And how can I avoid or
>> > workaround this problem?
>> >
>> > Thanks a lot.
>> >
>> > James Su
>> > _______________________________________________
>> > webkit-dev mailing list
>> > webkit-dev at lists.webkit.org
>> > http://lists.webkit.org/mailman/listinfo.cgi/webkit-dev
>> >
>>
>>
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