Re: [Qemu-devel] [PATCH] Revived GUEST_BASE support for usermode emulation targets [v3]

[Riku Voipio]

On Tue, May 05, 2009 at 02:53:31PM +0100, Paul Brook wrote:
> On Tuesday 05 May 2009, Riku Voipio wrote:
> > +++ b/tcg/x86_64/tcg-target.c
> > @@ -616,15 +616,15 @@ static void tcg_out_qemu_ld(TCGContext *s, const
> >          /* movzbl */
> > -        tcg_out_modrm_offset(s, 0xb6 | P_EXT, data_reg, r0, 0);
> > +        tcg_out_modrm_offset(s, 0xb6 | P_EXT, data_reg, r0, GUEST_BASE);

> This breaks when GUEST_BASE is large.

usually we don't set it to very large, just high enough to overcome
mmap_min_addr limits.

> 32-bit x86 is probably ok because GUEST_BASE is always a 32-bit value. This 
> is 
> not true for x86-64. Incidentally tcg_out_modrm doesn't seem to check this, 
> and silently generates broken code.

Should we rather check for a mazimum size on guest_base or revert to the lea 
-based
version?