Incorrect Behaviour: Arm64 CopyLdrLiteral rewrites Prefetch as Memory Read, which can Trash a Potentially Used Register

Describe the bug

This is a sister bug to:

• #305

In the following detours code

https://github.com/microsoft/Detours/blob/4b8c659f549b0ab21cf649377c7a84eb708f5e68/src/disasm.cpp#L4226-L4261

which rewrites LDR Literal, the PRFM (Prefetch) instruction is rewritten as a load.

This happens because LDR literal and PRFM use the same opcode, and thus the LDR code path would be used for PRFM

https://github.com/microsoft/Detours/blob/4b8c659f549b0ab21cf649377c7a84eb708f5e68/src/disasm.cpp#L3967-L3969

e.g. PRFM PLIL1KEEP, #0 is 0xD8000008. (0xD8000008 & 0x3b000000) == 0x18000000 is true, thus the LDR code path is executed for PRFM.

Expected behavior

Prefetch operation should not be rewritten as a load, as this will trash the existing value in the register, which may still be used by the function.

Additional context

I'm building a cross platform, multi architecture hooking library [big WIP]; and I found detours' source to be pretty invaluable as a reference for code rewriting.

This is just a small thing I noticed while working on code rewriting on my end while referencing detours.

Start in src/disasm.cpp at the LDR literal handling around lines 4226-4261 and the opcode check around lines 3967-3969. Compare the referenced ARM documentation and the PRFM PLIL1KEEP, #0 encoding; done means a prefetch is not rewritten as a load or used to overwrite the existing register value.