[PATCH v2 0/3] objtool: Support the stack swizzle

[Peter Zijlstra]

Hi!

Implement objtool support for the x86_64 stack swizzle pattern.

This means we can use the minial stack swizzle:

  mov %rsp, (%[tos])
  mov %[tos], %rsp
  ...
  pop %rsp

from inline asm, with arbitrary stack setup. The ORC data for the Top-of-Stack
will use the SP_INDIRECT CFA base. In order for this to work, SP_INDIRECT needs
to first dereference and then add the offset to find the next frame.

Therefore we need to change SP_INDIRECT (which is currently unused) to mean:
(%rsp) + offset.

Changes since v1 include:

 - removed the !callee saved reg restriction by using the vals[] array
   over the regs[] array.

 - per the above, removed the patches creating the regs[] scratch space.

 - more comments.

 - rebased to tip/objtool/core