Re: [Qemu-devel] qemu-arm: wrong execution of post-indexed loads when Rm and Rd are the same register

[Rodrigo Vivi]

Hi Paul,

On 3/15/07, Paul Brook <address@hidden> wrote:
> On Thursday 15 March 2007 19:35, Lauro Ramos Venancio wrote:
> > Qemu-arm is wrongly executing post-indexed loads when Rm and Rd are
> > the same register. For example:
> >
> > ldr r0, [r1], +r0
> >
> > Current behavior:
> > r0 <- [r1]
> > r1 <- r1 + r0
> >
> > Expected behavior:
> > addr <- r1
> > r1 <- r1 + r0
> > r0 <- [addr]
>
> This is still wrong.
So, is this a known bug?

> The writeback must happen after the load.
We code like this because
- we didn't find this restriction in arm reference manual
- the LLVM uses this instruction expecting a result like this
- That was the result that we got running these instructions in an OMAP1710

> Your
> implementation will give incorrect results if the load faults.

Another thing, is that in this manual (at page A2-18) there are 2
rules for data abort:
- Base Restored Abort Model and Base Updated Abort Model.

So, we can not understand why it will give incorect results if a load faults...

> Paul

thanks
Rodrigo Vivi
vivijim at freenode

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