runtime: use explicit NOFRAME on freebsd/amd64

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

Updates #58378

Change-Id: Ibd00748946f1137e165293df7da73278cb673bbd
Reviewed-on: https://go-review.googlesource.com/c/go/+/466395
Reviewed-by: Than McIntosh <thanm@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Run-TryBot: Quim Muntal <quimmuntal@gmail.com>

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

@@ -613,7 +613,8 @@ 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:
+	case objabi.Hwindows, objabi.Hdarwin, objabi.Hlinux, objabi.Hdragonfly,
+		objabi.Hfreebsd:
 	default:
 		usefpheuristic = true
 	}

src/runtime/sys_freebsd_amd64.s

@@ -251,16 +251,14 @@ 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()
 
@@ -285,7 +283,7 @@ TEXT runtime·sigtramp(SB),NOSPLIT|TOPFRAME,$0
 	RET
 
 // Called using C ABI.
-TEXT runtime·sigprofNonGoWrapper<>(SB),NOSPLIT,$0
+TEXT runtime·sigprofNonGoWrapper<>(SB),NOSPLIT|NOFRAME,$0
 	// Transition from C ABI to Go ABI.
 	PUSH_REGS_HOST_TO_ABI0()