[Webkit-unassigned] [Bug 130638] [Win64] ASM LLINT is not enabled.

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=130638





--- Comment #44 from peavo at outlook.com  2014-05-26 13:33:30 PST ---
(In reply to comment #42)
> (In reply to comment #40)
> > (From update of attachment 231527 [details] [details])
> > View in context: https://bugs.webkit.org/attachment.cgi?id=231527&action=review
> > 
>  
> > > Source/JavaScriptCore/assembler/MacroAssemblerX86_64.h:162
> > > +        store64(X86Registers::ebp, Address(X86Registers::esp, -16));
> > 
> > Why do we need to preserve the ebp here?  According to http://msdn.microsoft.com/en-us/library/6t169e9c.aspx, ebp is non-volatile.
> > 
> 
> This is not done to preserve ebp.
> As I've understood it, for a host function call, JIT relies on that the frame pointer is put on the stack after the return address.
> The first parameter of a host function call (ExecState *), will then point to the value of the frame pointer.
> Since MSVC does not maintain the frame pointer on 64-bit, we have to do this manually on Windows.
> Without this, I get many crashes/failures running the stress tests.
> 

Fixed incorrect comment in latest patch.
It is the CallerFrame (frame pointer) that needs to be stored manually at the correct location on the stack, since we cannot rely on MSVC to do this.

> > 
> > > Source/JavaScriptCore/llint/LowLevelInterpreter64.asm:327
> > > +    elsif X86_64_WIN
> > > +        # On Win64 we need to manually copy the frame pointer to the stack, since MSVC may not maintain a frame pointer on 64-bit.
> > > +        # See http://msdn.microsoft.com/en-us/library/9z1stfyw.aspx where it's stated that rbp MAY be used as a frame pointer.
> > > +        # Also, we need to manually copy the return address to the stack, since before the call instruction we allocated space
> > > +        # for the 4 parameter registers, and the call instruction won't put the return address at the correct stack location.
> > > +        move sp, t2
> > > +        storep cfr, [sp]
> > > +        call .copyReturnAddressToStack
> > > +.copyReturnAddressToStack:
> > > +        pop 8[sp]
> > > +        # Adjust the return address with the offset to the instruction after the call instruction.
> > > +        addp 16, 8[sp]
> > 
> > Apart from the "move sp, t2", why do we need to do this?   The rbp is a non-volatile register even if it's not used as a frame pointer.
> 
> I have removed the calculation of the return address, since it's not really needed, as you mentioned earlier.
> Storing the frame pointer on the stack is needed, I believe, since JIT relies on that the frame pointer is put on the stack, and MSVC does not maintain the frame pointer.
> The first parameter of the host function call (ExecState *), will then point to the value of the frame pointer.
> The same is also done in the CLOOP case.

Fixed incorrect comment in latest patch.
It is the CallerFrame (frame pointer) that needs to be stored manually at the correct location on the stack, since we cannot rely on MSVC to do this.

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