The existing code for recover from deferrangefunc was broken in
several ways.
1. the code following a deferrangefunc call did not check the return
value for an out-of-band value indicating "return now" (i.e., recover
was called)
2. the returned value was delivered using a bespoke ABI that happened
to match on register-ABI platforms, but not on older stack-based
ABI.
3. the returned value was the wrong width (1 word versus 2) and
type/value(integer 1, not a pointer to anything) for deferrangefunc's
any-typed return value (in practice, the OOB value check could catch
this, but still, it's sketchy).
This -- using the deferreturn lookup method already in place for
open-coded defers -- turned out to be a much-less-ugly way of
obtaining the desired transfer of control for recover().
TODO: we also could do this for regular defer, and delete some code.
Fixes#71675
Change-Id: If7d7ea789ad4320821aab3b443759a7d71647ff0
Reviewed-on: https://go-review.googlesource.com/c/go/+/650476
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>
