runtime: asynchronous preemption function for x86

This adds asynchronous preemption function for amd64 and 386. These
functions spill and restore all register state that can be used by
user Go code.

For the moment we stub out the other arches.

For #10958, #24543.

Change-Id: I6f93fabe9875f4834922a5712362e79045c00aca
Reviewed-on: https://go-review.googlesource.com/c/go/+/201759
Run-TryBot: Austin Clements <austin@google.com>
Reviewed-by: Cherry Zhang <cherryyz@google.com>

1 files changed, 15 insertions, 0 deletions

diff --git a/src/runtime/preempt.go b/src/runtime/preempt.go
index 96eaa3488b..57ec493b8d 100644
--- a/src/runtime/preempt.go
+++ b/src/runtime/preempt.go
@@ -232,3 +232,18 @@ func resumeG(state suspendGState) {
 func canPreemptM(mp *m) bool {
 	return mp.locks == 0 && mp.mallocing == 0 && mp.preemptoff == "" && mp.p.ptr().status == _Prunning
 }
+
+//go:generate go run mkpreempt.go
+
+// asyncPreempt saves all user registers and calls asyncPreempt2.
+//
+// When stack scanning encounters an asyncPreempt frame, it scans that
+// frame and its parent frame conservatively.
+//
+// asyncPreempt is implemented in assembly.
+func asyncPreempt()
+
+//go:nosplit
+func asyncPreempt2() {
+	// TODO: Enter scheduler
+}