Re: [Qemu-devel] target-ppc: Problem with mtmsr emulation

[Thomas Huth <thuth@linux.vnet.ibm.com>]

On Fri, 28 Mar 2014 18:25:02 +0800
Alexander Graf <agraf@suse.de> wrote:

> 
> 
> > Am 28.03.2014 um 16:16 schrieb Thomas Huth <thuth@linux.vnet.ibm.com>:
> > 
> > 
> > Hi all!
> > 
> > There seems to be a problem with the emulation of the mtmsr instruction:
> > According to the PowerISA spec, chapter Book III-S, the mtmsr opcode
> > has a so-called "L" field at bit position 15. Looking at the function
> > gen_mtmsr() in target-ppc/translate.c, the bit is taken into account
> > since the function checks for ctx->opcode & 0x00010000.
> > However, when looking at the GEN_HANDLER definition later in that file:
> > 
> > GEN_HANDLER(mtmsr, 0x1F, 0x12, 0x04, 0x001FF801, PPC_MISC)
> > 
> > you can see that the bit is marked as invalid bit in the 0x001FF801
> > mask, thus if the bit is set, a program exception is generated instead
> > of executing the gen_mtmsr() function.
> > 
> > An easy way to fix this for Book III-S is to change the mask to
> > 0x001EF801 (just like the mask for mtmsrd), but I am afraid that this
> > would break the Book III-E variant of mtmsr, since the embedded version
> > does not have this bit defined. Any suggestions how to fix this problem
> > in a proper way?
> 
> Please check in the older isa versions whether that bit is declared reserved.
> 
> If it is, we need to make sure we only match it on newer ISA conformance.

The oldest ISA version that I've found (version 2.01, from 2003) already
contains the L bit, so I assume it's always been there. So it's likely
just a Book III-S vs. Book III-E issue.

 Thomas