[LLVMdev] How to Find Instruction Encoding for a MachineInstr
criswell at illinois.edu
Tue Oct 23 11:58:48 PDT 2012
I'm enhancing a MachineFunctionPass that enforces control-flow
integrity. One of the things I want to do is to set the alignment of an
instruction (by adding NOPs before it in the MachineBasicBlock or by
emitting an alignment directive to the assembler) if it causes a
specific sequence of bytes to be generated at a specific alignment. The
goal is to ensure that sequences of bytes used to label valid targets of
an indirect branch (e.g., a return instruction) do not appear at a given
alignment anywhere in a program other than for where I inserted them
It looks like MachineInstr has a method for finding the length of the
instruction's binary encoding, but I didn't see a method for finding the
exact bytes that would be emitted from the MachineInstr. Is there a way
to do this in the MachineFunctionPass/MachineInstr infrastructure, or do
I need to use something like the MC classes?
Thanks in advance for any help provided.
-- John T.
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