[RFC] Objtool toolchain proposal: -fannotate-{jump-table,noreturn}

[Peter Zijlstra]

On Thu, Sep 15, 2022 at 10:56:58AM +0800, Chen Zhongjin wrote:

> We have found some anonymous information on x86 in .rodata.

Well yes, but that's still a bunch of heuristics on our side.

> I'm not sure if those are *all* of Josh wanted on x86, however for arm64 we
> did not found that in the same section so it is a problem on arm64 now.

Nick found Bolt managed the ARM64 jumptables:

  https://github.com/llvm/llvm-project/blob/main/bolt/lib/Target/AArch64/AArch64MCPlusBuilder.cpp#L484

But that does look like a less than ideal solution too.

> Does the compiler will emit these for all arches? At lease I tried and
> didn't find anything meaningful (maybe I omitted it).

That's the question; can we get the compiler to help us here in a well
defined manner.