runtime: use explicit NOFRAME on netbsd/amd64

This CL marks some netbsd assembly functions as NOFRAME to avoid
relying on the implicit amd64 NOFRAME heuristic, where NOSPLIT functions
without stack were also marked as NOFRAME.

While here, and thanks to CL 466355, `asm_netbsd_amd64.s` can
be deleted in favor of `asm9_unix2_amd64.s`, which makes better
use of the frame pointer.

Updates #58378

Change-Id: Iff554b664ec25f2bb6ec198c0f684590b359c383
Reviewed-on: https://go-review.googlesource.com/c/go/+/466396
Reviewed-by: Than McIntosh <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
Reviewed-by: Cherry Mui <[email protected]>
Run-TryBot: Quim Muntal <[email protected]>

Author: qmuntal

src/cmd/internal/obj/x86/obj6.go

@@ -614,7 +614,7 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
 	var usefpheuristic bool
 	switch ctxt.Headtype {
 	case objabi.Hwindows, objabi.Hdarwin, objabi.Hlinux, objabi.Hdragonfly,
-		objabi.Hfreebsd:
+		objabi.Hfreebsd, objabi.Hnetbsd:
 	default:
 		usefpheuristic = true
 	}

src/runtime/sys_netbsd_amd64.s

@@ -296,16 +296,14 @@ TEXT runtime·sigfwd(SB),NOSPLIT,$0-32
 	MOVL	sig+8(FP),   DI
 	MOVQ	info+16(FP), SI
 	MOVQ	ctx+24(FP),  DX
-	PUSHQ	BP
-	MOVQ	SP, BP
-	ANDQ	$~15, SP     // alignment for x86_64 ABI
+	MOVQ	SP, BX		// callee-saved
+	ANDQ	$~15, SP	// alignment for x86_64 ABI
 	CALL	AX
-	MOVQ	BP, SP
-	POPQ	BP
+	MOVQ	BX, SP
 	RET
 
 // Called using C ABI.
-TEXT runtime·sigtramp(SB),NOSPLIT|TOPFRAME,$0
+TEXT runtime·sigtramp(SB),NOSPLIT|TOPFRAME|NOFRAME,$0
 	// Transition from C ABI to Go ABI.
 	PUSH_REGS_HOST_TO_ABI0()
 

src/syscall/asm9_unix2_amd64.s

@@ -2,13 +2,13 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-//go:build dragonfly || freebsd
+//go:build dragonfly || freebsd || netbsd
 
 #include "textflag.h"
 #include "funcdata.h"
 
 //
-// Syscall9 support for AMD64, DragonFly and FreeBSD
+// Syscall9 support for AMD64, DragonFly, FreeBSD and NetBSD
 //
 
 // func Syscall9(trap int64, a1, a2, a3, a4, a5, a6, a7, a8, a9 int64) (r1, r2, err int64);