On 12/15/2009 08:48 PM, Clemens Kolbitsch wrote:
Hi list,
I'm experiencing a strange emulation bug with the op-code below. The
instruction raises a segfault in the application (running on the guest),
however, if I enable KVM to run the exact same application, no segfault is
raised.
0x0080023b: 8b 04 65 11 22 33 44 mov regEAX, [0x44332211]
where "11 22 33 44" is just some address. According to gdb (on a 32bit little-
endian machine), this instruction can be disassembled as a "mov address to
reg-eax".
This is an odd encoding for this instruction, since there is a shorter
one possible (8b 05 11 22 33 44). So it is possible there is a bug in
qemu that has never been triggered because compilers/assemblers don't
generate this encoding.
btw, binutils disassembles this as
8b 04 65 11 22 33 44 mov 0x44332211(,%eiz,2),%eax
I guess %eiz is some mnemonic for a "zero register" so the assembly can
be reassembled into a 7-byte instruction later.
--
Do not meddle in the internals of kernels, for they are subtle and quick to
panic.
