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From: Paul Brook <paul@codesourcery.com>
Subject: Re: [Qemu-devel] [PATCH] sh4: define explicitly that the target CPU
	is 32 bit
Date: Fri, 30 Nov 2007 17:15:21 +0000
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To: qemu-devel@nongnu.org

On Friday 30 November 2007, Carlo Marcelo Arenas Belon wrote:
> On Fri, Nov 30, 2007 at 04:28:09PM +0000, Paul Brook wrote:
> > On Friday 30 November 2007, Carlo Marcelo Arenas Belon wrote:
> > > The following patch enforces that the sh4 target is 32 bit to prevent
> > > qemu to expand incorrectly to a 64 bit wide cpu if compiled in a 64 bit
> > > host.
> >
> > This is wrong. As the comment in cpu-defs.h says, target_phys_addr_t may
> > need to be bigger than the actual target address space.
> >
> > What exactly are you trying to fix?
>
> in a generic way, that the CPU width of the host (as defined by the size of
> the type that is used to store a target_phys_addr_t) that is used to build
> the emulator affects in any way the size of the emulated target physical
> address size or its representation.
>
> in the sh4 specific case, it doesn't make sense for sh4 to print an access
> error to a physical address that is 64 bit long when it is a 32 bit CPU and
> that is what would happen unless the patch is applied.
>
> if anything the following definition from cpu-defs.h is invalid for a
> representation of a 32 bit physical address :
>
> #define TARGET_FMT_plx "%016" PRIx64

Before you can fix that you probably need to fix the bits of qemu (TLB code) 
that store a host pointer in a phys_addr_t. Or at least distance 
TARGET_PHYS_ADDR_BITS from the definition of phys_addr_t, and include 
appropriate comments.

In that case TARGET_PHYS_ADDR_BITS could be a precise value, rather than the 
next multiple of 32. e.g. I think sparc32 has a 40-bit physical address 
space.

Paul