[LLVMdev] LLVM IR, Instructions, Backend, AsmPrinter

[John Criswell]

On 6/18/14, 3:01 AM, pratik dand wrote:
> Dear,
>
> I am new to llvm and hence have very little idea about a problem that 
> is my university project.
> I am supposed to assume a X86 CPU supporting an instruction ADDenc 
> that adds two encrypted operands. The original ADD also exists and 
> should operate on unencrypted operands.
>
> My task is to transform C programs into the new X86 assembly that 
> supports ADDenc. I have very little idea about this.
>
> I have been suggested the following approaches
> 1) Adding a new Instruction ADDenc in the current X86 LLVM backend and 
> make the necessary changes.
> 2) Adding a new LLVM IR instruction addenc that recognises the 
> operands at this level instead of general LLVM add, then add an 
> instruction in the target X86 to transform addenc of LLVM to ADDenc of 
> X86.

There is a third option: if you have an assembler that understands the 
new ADDenc instruction, you can probably add inline assembly code that 
performs the AddEnc instruction.  This will only work if you're doing 
ahead-of-time compilation and clang is configured to use your new 
assembler, but if you're transforming C code, that is most likely what 
you're doing.

That said, if you're sufficiently confident with working with the LLVM 
code generator, I think you should add support for the AddEnc 
instruction in the X86 Backend.  As to whether you should add an 
intrinsic or modify the backend to just figure out where to use AddEnc, 
I'm guessing that adding an intrinsic would be better, but people more 
familiar with the code generator infrastructure should comment.

Regards,

John Criswell

>
> I have been given an LLVM pass that can run on LLVM IR and decide 
> which are the encrypted operands.
>
> Any help of any kind will be helpful as I know very little about LLVM.
>
> -- 
> Pratik
>
>
>
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