Re: How to disassemble problematic sequence of bytes (ia32)

En news:4b14ba0f-cddb-4706-a4eb-d0df3717a50e@xxxxxxxxxxxxxxxxxxxxxxxxxxxx,
notpyrc va escriure:
My problem is that recently I have been trying to properly interpret
this sequence of code (ia32)

Code:
db 0x66, 0xF3, 0x0F, 0x10 (...)

Intel reference says that the sequence refers to either "movss Vss,
Wss" (prefix F3) or "movupd Vpd, Wpd" (prefix 66). The question arises
how this sequence should be recognized with both prefixes ?

If I remember correctly (did not test it right now however), the real result
is #UD (illegal opcode).

So probably the first prefix (0x66 here) should be decoded in isolation
(since it won't behave as a SSE instruction anyway); then you decode the
rest as normal SSE (here movss); this way you cater correctly with someone
branching directly at the 0xF3 byte.


Antoine

.

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