runtime: remove unused arm assembly for div/mod

Also add runtime· prefixes to the code that is still used.

Fixes #19507

Change-Id: Ib6da6b2a9e398061d3f93958ee1258295b6cc33b
Reviewed-on: https://go-review.googlesource.com/45699Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/cmd/internal/obj/arm/obj5.go

@@ -637,7 +637,7 @@ func (c *ctxt5) softfloat() {
 		return
 	}
 
-	symsfloat := c.ctxt.Lookup("_sfloat")
+	symsfloat := c.ctxt.Lookup("runtime._sfloat")
 
 	wasfloat := 0
 	for p := c.cursym.Func.Text; p != nil; p = p.Link {
@@ -689,7 +689,7 @@ func (c *ctxt5) softfloat() {
 			next = c.newprog()
 			*next = *p
 
-			// BL _sfloat(SB)
+			// BL runtime·_sfloat(SB)
 			*p = obj.Prog{}
 			p.Ctxt = c.ctxt
 			p.Link = next

src/cmd/vet/all/whitelist/arm.txt

@@ -19,7 +19,6 @@ runtime/duff_arm.s: [arm] duffcopy: function duffcopy missing Go declaration
 runtime/tls_arm.s: [arm] save_g: function save_g missing Go declaration
 runtime/tls_arm.s: [arm] load_g: function load_g missing Go declaration
 runtime/tls_arm.s: [arm] _initcgo: function _initcgo missing Go declaration
-runtime/vlop_arm.s: [arm] udiv: function udiv missing Go declaration
 
 // Clearer using FP than SP, but that requires named offsets.
 runtime/asm_arm.s: [arm] rt0_go: use of 4(R13) points beyond argument frame

src/runtime/softfloat_arm.go

@@ -653,3 +653,8 @@ func sfloat2(pc uint32, regs *[15]uint32) uint32 {
 	}
 	return pc
 }
+
+// Stubs to pacify vet. Not safe to call from Go.
+// Calls to these functions are inserted by the compiler.
+func _sfloat()
+func udiv()

src/runtime/vlop_arm.s

@@ -28,26 +28,10 @@
 #include "funcdata.h"
 #include "textflag.h"
 
-/* replaced use of R10 by R11 because the former can be the data segment base register */
-
-TEXT _mulv(SB), NOSPLIT, $0
-	MOVW	l0+0(FP), R2	/* l0 */
-	MOVW	h0+4(FP), R11	/* h0 */
-	MOVW	l1+8(FP), R4	/* l1 */
-	MOVW	h1+12(FP), R5	/* h1 */
-	MULLU	R4, R2, (R7,R6)
-	MUL	R11, R4, R8
-	ADD	R8, R7
-	MUL	R2, R5, R8
-	ADD	R8, R7
-	MOVW	R6, ret_lo+16(FP)
-	MOVW	R7, ret_hi+20(FP)
-	RET
-
 // trampoline for _sfloat2. passes LR as arg0 and
 // saves registers R0-R13 and CPSR on the stack. R0-R12 and CPSR flags can
 // be changed by _sfloat2.
-TEXT _sfloat(SB), NOSPLIT, $68-0 // 4 arg + 14*4 saved regs + cpsr + return value
+TEXT runtime·_sfloat(SB), NOSPLIT, $68-0 // 4 arg + 14*4 saved regs + cpsr + return value
 	MOVW	R14, 4(R13)
 	MOVW	R0, 8(R13)
 	MOVW	$12(R13), R0
@@ -215,118 +199,6 @@ DATA fast_udiv_tab<>+0x38(SB)/4, $0x85868788
 DATA fast_udiv_tab<>+0x3c(SB)/4, $0x81828384
 GLOBL fast_udiv_tab<>(SB), RODATA, $64
 
-// The linker will pass numerator in R8
-#define Rn R8
-// The linker expects the result in RTMP
-#define RTMP R11
-
-TEXT _divu(SB), NOSPLIT, $16-0
-	// It's not strictly true that there are no local pointers.
-	// It could be that the saved registers Rq, Rr, Rs, and Rm
-	// contain pointers. However, the only way this can matter
-	// is if the stack grows (which it can't, udiv is nosplit)
-	// or if a fault happens and more frames are added to
-	// the stack due to deferred functions.
-	// In the latter case, the stack can grow arbitrarily,
-	// and garbage collection can happen, and those
-	// operations care about pointers, but in that case
-	// the calling frame is dead, and so are the saved
-	// registers. So we can claim there are no pointers here.
-	NO_LOCAL_POINTERS
-	MOVW	Rq, 4(R13)
-	MOVW	Rr, 8(R13)
-	MOVW	Rs, 12(R13)
-	MOVW	RM, 16(R13)
-
-	MOVW	Rn, Rr			/* numerator */
-	MOVW	g_m(g), Rq
-	MOVW	m_divmod(Rq), Rq	/* denominator */
-	BL  	runtime·udiv(SB)
-	MOVW	Rq, RTMP
-	MOVW	4(R13), Rq
-	MOVW	8(R13), Rr
-	MOVW	12(R13), Rs
-	MOVW	16(R13), RM
-	RET
-
-TEXT _modu(SB), NOSPLIT, $16-0
-	NO_LOCAL_POINTERS
-	MOVW	Rq, 4(R13)
-	MOVW	Rr, 8(R13)
-	MOVW	Rs, 12(R13)
-	MOVW	RM, 16(R13)
-
-	MOVW	Rn, Rr			/* numerator */
-	MOVW	g_m(g), Rq
-	MOVW	m_divmod(Rq), Rq	/* denominator */
-	BL  	runtime·udiv(SB)
-	MOVW	Rr, RTMP
-	MOVW	4(R13), Rq
-	MOVW	8(R13), Rr
-	MOVW	12(R13), Rs
-	MOVW	16(R13), RM
-	RET
-
-TEXT _div(SB),NOSPLIT,$16-0
-	NO_LOCAL_POINTERS
-	MOVW	Rq, 4(R13)
-	MOVW	Rr, 8(R13)
-	MOVW	Rs, 12(R13)
-	MOVW	RM, 16(R13)
-	MOVW	Rn, Rr			/* numerator */
-	MOVW	g_m(g), Rq
-	MOVW	m_divmod(Rq), Rq	/* denominator */
-	CMP 	$0, Rr
-	BGE 	d1
-	RSB 	$0, Rr, Rr
-	CMP 	$0, Rq
-	BGE 	d2
-	RSB 	$0, Rq, Rq
-d0:
-	BL  	runtime·udiv(SB)  	/* none/both neg */
-	MOVW	Rq, RTMP
-	B	out1
-d1:
-	CMP 	$0, Rq
-	BGE 	d0
-	RSB 	$0, Rq, Rq
-d2:
-	BL  	runtime·udiv(SB)  	/* one neg */
-	RSB	$0, Rq, RTMP
-out1:
-	MOVW	4(R13), Rq
-	MOVW	8(R13), Rr
-	MOVW	12(R13), Rs
-	MOVW	16(R13), RM
-	RET
-
-TEXT _mod(SB),NOSPLIT,$16-0
-	NO_LOCAL_POINTERS
-	MOVW	Rq, 4(R13)
-	MOVW	Rr, 8(R13)
-	MOVW	Rs, 12(R13)
-	MOVW	RM, 16(R13)
-	MOVW	Rn, Rr			/* numerator */
-	MOVW	g_m(g), Rq
-	MOVW	m_divmod(Rq), Rq	/* denominator */
-	CMP 	$0, Rq
-	RSB.LT	$0, Rq, Rq
-	CMP 	$0, Rr
-	BGE 	m1
-	RSB 	$0, Rr, Rr
-	BL  	runtime·udiv(SB)  	/* neg numerator */
-	RSB 	$0, Rr, RTMP
-	B   	out
-m1:
-	BL  	runtime·udiv(SB)  	/* pos numerator */
-	MOVW	Rr, RTMP
-out:
-	MOVW	4(R13), Rq
-	MOVW	8(R13), Rr
-	MOVW	12(R13), Rs
-	MOVW	16(R13), RM
-	RET
-
 // _mul64by32 and _div64by32 not implemented on arm
 TEXT runtime·_mul64by32(SB), NOSPLIT, $0
 	MOVW	$0, R0