reflect: cram method dispatch into one memory page

For golang#38783

Author: TheCount

src/cmd/internal/obj/x86/asm6.go

@@ -2044,8 +2044,8 @@ type nopPad struct {
 // cursym: current function being assembled
 // returns number of bytes of padding needed
 func addpad(pc, a int64, ctxt *obj.Link, cursym *obj.LSym) int {
-	if !((a&(a-1) == 0) && 8 <= a && a <= 2048) {
-		ctxt.Diag("alignment value of an instruction must be a power of two and in the range [8, 2048], got %d\n", a)
+	if !((a&(a-1) == 0) && 8 <= a && a <= 4096) {
+		ctxt.Diag("alignment value of an instruction must be a power of two and in the range [8, 4096], got %d\n", a)
 		return 0
 	}
 

src/reflect/asm_amd64.s

@@ -83,6 +83,8 @@ TEXT ·methodValueCall(SB),(NOSPLIT|WRAPPER),$312
 // the closure which implements the method.
 // No preamble of any kind, we need to do things manually.
 TEXT ·dispatchToMethod<ABIInternal>(SB),(NOSPLIT|NOFRAME),$0-0
+	// cram dispatchToMethod and dispatchLabel into a single memory page
+	PCALIGN $4096
 	CALL ·dispatchLabel(SB)
 	CALL ·dispatchLabel(SB)
 	CALL ·dispatchLabel(SB)