addpad between 8 and 2048, fix tests

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

@@ -2036,22 +2036,28 @@ type nopPad struct {
 	n int32     // Size of the pad
 }
 
-// padding bytes to add to align code as requested.
+// Padding bytes to add to align code as requested.
+// Alignment is restricted to powers of 2 between 8 and 2048 inclusive.
+//
+// pc: current offset in function, in bytes
+// a: requested alignment, in bytes
+// cursym: current function being assembled
+// returns number of bytes of padding needed
 func addpad(pc, a int64, ctxt *obj.Link, cursym *obj.LSym) int {
-	switch a {
-	case 8, 16, 32, 64:
-		// By default function alignment is 16. If an alignment > 16 is
-		// requested then the function alignment must also be promoted.
-		// The function alignment is not promoted on AIX at this time.
-		if cursym.Func().Align < int32(a) {
-			cursym.Func().Align = int32(a)
-		}
-		if pc&(a-1) != 0 {
-			return int(a - (pc & (a - 1)))
-		}
-	default:
-		ctxt.Diag("Unexpected alignment: %d for PCALIGN directive\n", a)
+	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)
+		return 0
 	}
+
+	// By default function alignment is 32 bytes for amd64
+	if cursym.Func().Align < int32(a) {
+		cursym.Func().Align = int32(a)
+	}
+
+	if pc&(a-1) != 0 {
+		return int(a - (pc & (a - 1)))
+	}
+
 	return 0
 }
 

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

@@ -313,12 +313,12 @@ func TestPCALIGN(t *testing.T) {
 	}{
 		{
 			name: "8-byte alignment",
-			code: `TEXT ·foo(SB),$0-0\nMOVQ $0, AX\nPCALIGN $8\nMOVQ $1, BX\nRET\n`,
+			code: "TEXT ·foo(SB),$0-0\nMOVQ $0, AX\nPCALIGN $8\nMOVQ $1, BX\nRET\n",
 			out:  `0x0008\s00008\s\(.*\)\tMOVQ\t\$1,\sBX`,
 		},
 		{
 			name: "16-byte alignment",
-			code: `TEXT ·foo(SB),$0-0\nMOVQ $0, AX\nPCALIGN $16\nMOVQ $2, CX\nRET\n`,
+			code: "TEXT ·foo(SB),$0-0\nMOVQ $0, AX\nPCALIGN $16\nMOVQ $2, CX\nRET\n",
 			out:  `0x0010\s00016\s\(.*\)\tMOVQ\t\$2,\sCX`,
 		},
 	}