[llvm] [Dwarf][Transforms] Add dwarf support when func signature changed (PR #127855)

[via llvm-commits]

yonghong-song wrote:

> Do we want to do this unconditionally? If BPF is the only identified consumer, maybe not. But the size cost is low, so maybe not worth the trouble to make it conditioned on tuning or some other flag. @dwblaikie @adrian-prantl

Actually no. The intended consumer is x86, aarch64, etc. bpf is able to trace functions in those architectures to gather information inside the kernel. The signature change info (in dwarf) will help bpf users to *correctly* write their progs in order to trace those functions.

Ideally, bpf could like accurate function prototypes after transformation for those x86 etc. architectures. But the first step would to recognize that there is a signature change so users can either avoid such functions or try to dig into the asm codes by themselves to find true signature.

https://github.com/llvm/llvm-project/pull/127855