On 04/23/2014 01:53 PM, Nadav Amit wrote: >> >> Err, operand size is forced to 64-bits, not address size. >> >> "The following aspects of near branches are controlled by the effective >> operand size: >> • Truncation of the size of the instruction pointer" >> >> Still, "67h call" should not truncate EIP (which your patch does). >> > Yes, I missed it. > But if I am not mistaken again, it means that the existing > implementation of jmp_rel is broken as well when address-size override > prefix is used. In this case, as I see it, the existing masking would > cause the carry from the add operation to the lower half of the rip not > to be added to the rip higher half. > > I guess another patch is needed for that as well. > Yes, on x86 JMP really should be thought of as "MOV ...,IP/EIP/RIP". On some other architectures, e.g. m68k, JMP acts as if it was "LEA ...,PC", which causes some serious confusion for people familiar with that model. However, on x86 considering JMP as a MOV to the IP register really is very consistent and will give you the right mental model. -hpa -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
