[lldb] [llvm] [ELF][LLDB] Add an nvsass triple (PR #159459)

[Joseph Huber via llvm-commits]

jhuber6 wrote:

> @jhuber6 , something I care about for LLDB is being able to use different disassemblers for ptx and sass. The unique situation here is that sass is not part of LLVM code generation, and it seems that's why LLVM is unaware of sass. LLVM can only generate ptx and folks rely on an nvidia proprietary compiler to go from ptx to sass. But at runtime, LLDB sees both sass and nvptx.
> 
> I guess that a simpler patch that would exist only within LLDB is to add two flavors to the nvptx architecture, one for nvptx and for sass in the ArchSpec class in LLDB. I for sure can do that without doing major architectural changes like this.

LLVM's backend can only emit PTX, but as a toolchain we simply export that handling to `ptxas` as our assembler. The toolchain handles the binaries as the `nvptx64` triple because they correspond to ELF files created with `--target=nvptx64-nvidia-cuda`. You can generate SASS yourself with something similar to https://godbolt.org/z/ofWE6baPT. This is as far as I understand it at least, because as far as I'm aware, if a file has ELF magic and the `EM_CUDA` machine, it is SASS.

https://github.com/llvm/llvm-project/pull/159459