On Thu, 15 Sept 2022 at 10:47, Peter Zijlstra [off-list ref] wrote:

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

quoted

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

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

quoted

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.

quoted

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.

Do BTI landing pads help at all here? I.e., I assume that objtool just
treats any indirect call as a dangling edge in the control flow graph,
and the problem is identifying the valid targets. In the BTI case,
those will all start with a 'BTI J' instruction.