cmd/internal/obj/arm: check illegal base registers in ARM instructions

Wrong instructions "MOVW 8(F0), R1" and "MOVW R0<<0(F1), R1"
are silently accepted, and all Fx are treated as Rx.

The patch checks all those illegal base registers.

fixes #20724

Change-Id: I05d41bb43fe774b023205163b7daf4a846e9dc88
Reviewed-on: https://go-review.googlesource.com/46132
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>

src/cmd/asm/internal/asm/testdata/armerror.s

@@ -3,6 +3,32 @@
 // license that can be found in the LICENSE file.
 
 TEXT errors(SB),$0
+	MOVW	(F0), R1           // ERROR "illegal base register"
+	MOVB	(F0), R1           // ERROR "illegal base register"
+	MOVH	(F0), R1           // ERROR "illegal base register"
+	MOVF	(F0), F1           // ERROR "illegal base register"
+	MOVD	(F0), F1           // ERROR "illegal base register"
+	MOVW	R1, (F0)           // ERROR "illegal base register"
+	MOVB	R2, (F0)           // ERROR "illegal base register"
+	MOVH	R3, (F0)           // ERROR "illegal base register"
+	MOVF	F4, (F0)           // ERROR "illegal base register"
+	MOVD	F5, (F0)           // ERROR "illegal base register"
+	MOVM.IA	(F1), [R0-R4]      // ERROR "illegal base register"
+	MOVM.DA	(F1), [R0-R4]      // ERROR "illegal base register"
+	MOVM.IB	(F1), [R0-R4]      // ERROR "illegal base register"
+	MOVM.DB	(F1), [R0-R4]      // ERROR "illegal base register"
+	MOVM.IA	[R0-R4], (F1)      // ERROR "illegal base register"
+	MOVM.DA	[R0-R4], (F1)      // ERROR "illegal base register"
+	MOVM.IB	[R0-R4], (F1)      // ERROR "illegal base register"
+	MOVM.DB	[R0-R4], (F1)      // ERROR "illegal base register"
+	MOVW	R0<<0(F1), R1      // ERROR "illegal base register"
+	MOVB	R0<<0(F1), R1      // ERROR "illegal base register"
+	MOVW	R1, R0<<0(F1)      // ERROR "illegal base register"
+	MOVB	R2, R0<<0(F1)      // ERROR "illegal base register"
+	MOVF	0x00ffffff(F2), F1 // ERROR "illegal base register"
+	MOVD	0x00ffffff(F2), F1 // ERROR "illegal base register"
+	MOVF	F2, 0x00ffffff(F2) // ERROR "illegal base register"
+	MOVD	F2, 0x00ffffff(F2) // ERROR "illegal base register"
 	MULS.S	R1, R2, R3, R4     // ERROR "invalid .S suffix"
 	ADD.P	R1, R2, R3         // ERROR "invalid .P suffix"
 	SUB.W	R2, R3             // ERROR "invalid .W suffix"

src/cmd/internal/obj/arm/asm5.go

@@ -1343,6 +1343,27 @@ func (c *ctxt5) oplook(p *obj.Prog) *Optab {
 		}
 	}
 
+	// check illegal base register
+	switch a1 {
+	case C_SHIFT:
+		if p.From.Reg == 0 { // no base register
+			break
+		}
+		fallthrough
+	case C_SOREG, C_LOREG, C_HOREG, C_FOREG, C_ROREG, C_HFOREG, C_SROREG:
+		if p.From.Reg < REG_R0 || REG_R15 < p.From.Reg {
+			c.ctxt.Diag("illegal base register: %v", p)
+		}
+	default:
+	}
+	switch a3 {
+	case C_SOREG, C_LOREG, C_HOREG, C_FOREG, C_ROREG, C_HFOREG, C_SROREG, C_SHIFT:
+		if p.To.Reg < REG_R0 || REG_R15 < p.To.Reg {
+			c.ctxt.Diag("illegal base register: %v", p)
+		}
+	default:
+	}
+
 	// If current instruction has a .S suffix (flags update),
 	// we must use the constant pool instead of splitting it.
 	if (a1 == C_RCON2A || a1 == C_RCON2S) && p.Scond&C_SBIT != 0 {