Re: [Qemu-devel] sparc smul problem

["Blue Swirl" <blauwirbel@gmail.com>]

On 9/1/08, Blue Swirl <blauwirbel@gmail.com> wrote:
> On 9/1/08, Vince Weaver <vince@csl.cornell.edu> wrote:
>
> > Hello!
>  >
>  >  I've been stuck on this all weekend, as I can't find where the actual
>  > problem is. I might be completely missing it, but I've tried a lot of things
>  > and can't make it work.
>  >
>  >  On SPARC, the "smul" instruction multiplies two numbers, puts the result in
>  > the result register but also puts the top 32-bits of the 64-bit result into
>  > the "Y" register.
>  >
>  >  As the attached code shows, the value of "Y" is wrong.  Somehow after the
>  > multiply, the top 32 bits of the product rae all zeros.  I've played around
>  > with the code generated by translate.c, and it looks like the shift and
>  > other instructions all work properly, but the 64-bit multiply the result is
>  > somehow being truncated.  But I've looked at the generated code (on x86_64)
>  > and it looks like it is doing the right thing.
>  >
>  >  So anyway, I'll have to take a look at this again later, but in case anyone
>  > else wants to look at it in case I am missing anything obvious.
>
>
> It looks like TCG on i386 host generates incorrect code for mulu2_i32,
>  I think the op should be imul (unsigned) instead of mul. This patch
>  fixes the problem.

Never mind, I read the manuals wrong and the bug was elsewhere.