cmd/cgo: rewrite pointer passing rules in terms of pinning
With the introduction of runtime.Pinner, we need to update the cgo
pointer passing rules to accomodate the new functionality. These rule
changes are easier to describe if the rest of the pointer passing rules
are described in terms of pinning as well (Go memory is implicitly
pinned when a pointer to it is passed to a C function, and implicitly
unpinned when that function returns).
For #46787.
Change-Id: I263f03412bc9165f19c9ada72fb005ed0483a8ee
Reviewed-on: https://go-review.googlesource.com/c/go/+/498116 Reviewed-by: Austin Clements <austin@google.com> Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Auto-Submit: Michael Knyszek <mknyszek@google.com>