[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] Relocatable Xen early boot code
On 12/06/15 15:36, Daniel Kiper wrote: >> As stated at the hackathon, the problem with using %ebp is that it turns >> all implicit %ds references into implicit %ss references, and tends to > I am aware of that. However, I think that this is not a problem right > now because %ds == %ss. Some data segment attributes have different meanings when loaded into %ss, than when loaded into any of the plain data segment registers. I believe what we have is compatible between the two. but... > Additionally, I do not think that it will change in the future. Stack references behave differently to data references. For example, a non-canonical addresses generate a #GP fault for data references, or a #SS fault for stack references. The concern with implicit stack references comes from the subtle behaviour changes, not because it won't work in the general case. > >> add a SIB+imm32 to each instruction with a memory reference (ebp >> relative memory references, and r13 for that matter, have restrictions >> in the way in which they can be encoded). > I am not sure what are you talking about here. What do you mean by r13? > Register name? In 32-bit mode? Could you point me a paragraph in Intel > or AMD docs which says about this restrictions? This isn't a restriction pe say. It is a properly of ModRM/SIB encoding. It is described in both the Intel and AMD instruction reference manuals. ~Andrew _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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