runtime: fix uses of ABIInternal PCs in assembly

The covers three kinds of uses:

1. Calls of closures from assembly. These are always ABIInternal calls
without wrappers. I went through every indirect call in the runtime
and I think mcall is the only case of assembly calling a Go closure in
a way that's affected by ABIInternal. systemstack also calls a
closure, but it takes no arguments.

2. Calls of Go functions that expect raw ABIInternal pointers. I also
only found one of these: callbackasm1 -> cgocallback on Windows. These
are trickier to find, though.

3. Finally, I found one case on NetBSD where new OS threads were
directly calling the Go runtime entry-point from assembly via a PC,
rather than going through a wrapper. This meant new threads may not
have special registers set up. In this case, a change on all other
OSes had already forced new thread entry to go through an ABI wrapper,
so I just caught NetBSD up with that change.

With this change, I'm able to run a "hello world" with
GOEXPERIMENT=regabi,regabiargs.

For #40724.

Change-Id: I2a6d0e530c4fd4edf13484d923891c6160d683aa
Reviewed-on: https://go-review.googlesource.com/c/go/+/305669
Trust: Austin Clements <austin@google.com>
Run-TryBot: Austin Clements <austin@google.com>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Go Bot <gobot@golang.org>

1 files changed, 7 insertions, 3 deletions

diff --git a/src/runtime/os_netbsd.go b/src/runtime/os_netbsd.go
index 0328fa57ae..6fbb3aa694 100644
--- a/src/runtime/os_netbsd.go
+++ b/src/runtime/os_netbsd.go
@@ -228,7 +228,11 @@ func newosproc(mp *m) {
 	}
 }
 
-// netbsdMStart is the function call that starts executing a newly
+// mstart is the entry-point for new Ms.
+// It is written in assembly, uses ABI0, is marked TOPFRAME, and calls netbsdMstart0.
+func netbsdMstart()
+
+// netbsdMStart0 is the function call that starts executing a newly
 // created thread. On NetBSD, a new thread inherits the signal stack
 // of the creating thread. That confuses minit, so we remove that
 // signal stack here before calling the regular mstart. It's a bit
@@ -236,10 +240,10 @@ func newosproc(mp *m) {
 // it's a simple change that keeps NetBSD working like other OS's.
 // At this point all signals are blocked, so there is no race.
 //go:nosplit
-func netbsdMstart() {
+func netbsdMstart0() {
 	st := stackt{ss_flags: _SS_DISABLE}
 	sigaltstack(&st, nil)
-	mstart()
+	mstart0()
 }
 
 func osinit() {