[dev.cc] runtime: convert softfloat_arm.c to Go + build fixes

Also include onM_signalok fix from issue 8995.

Fixes linux/arm build.
Fixes #8995.

LGTM=r
R=r, dave
CC=golang-codereviews
https://golang.org/cl/168580043

src/runtime/asm_arm.s

@@ -55,7 +55,7 @@ TEXT runtime·rt0_go(SB),NOSPLIT,$-4
 nocgo:
 	// update stackguard after _cgo_init
 	MOVW	(g_stack+stack_lo)(g), R0
-	ADD	$const_StackGuard, R0
+	ADD	$const__StackGuard, R0
 	MOVW	R0, g_stackguard0(g)
 	MOVW	R0, g_stackguard1(g)
 
@@ -202,15 +202,17 @@ TEXT runtime·switchtoM(SB),NOSPLIT,$0-0
 	RET
 
 // func onM_signalok(fn func())
-TEXT runtime·onM_signalok(SB), NOSPLIT, $-4-4
+TEXT runtime·onM_signalok(SB), NOSPLIT, $4-4
 	MOVW	g_m(g), R1
 	MOVW	m_gsignal(R1), R2
+	MOVW	fn+0(FP), R0
 	CMP	g, R2
 	B.EQ	ongsignal
-	B	runtime·onM(SB)
+	MOVW	R0, 4(R13)
+	BL	runtime·onM(SB)
+	RET
 
 ongsignal:
-	MOVW	fn+0(FP), R0
 	MOVW	R0, R7
 	MOVW	0(R0), R0
 	BL	(R0)

src/runtime/softfloat64.go

@@ -340,7 +340,7 @@ func f32to64(f uint32) uint64 {
 	return fpack64(fs64, uint64(fm)<<d, fe, 0)
 }
 
-func fcmp64(f, g uint64) (cmp int, isnan bool) {
+func fcmp64(f, g uint64) (cmp int32, isnan bool) {
 	fs, fm, _, fi, fn := funpack64(f)
 	gs, gm, _, gi, gn := funpack64(g)
 
@@ -486,13 +486,13 @@ again2:
 
 // callable from C
 
-func fadd64c(f, g uint64, ret *uint64)            { *ret = fadd64(f, g) }
-func fsub64c(f, g uint64, ret *uint64)            { *ret = fsub64(f, g) }
-func fmul64c(f, g uint64, ret *uint64)            { *ret = fmul64(f, g) }
-func fdiv64c(f, g uint64, ret *uint64)            { *ret = fdiv64(f, g) }
-func fneg64c(f uint64, ret *uint64)               { *ret = fneg64(f) }
-func f32to64c(f uint32, ret *uint64)              { *ret = f32to64(f) }
-func f64to32c(f uint64, ret *uint32)              { *ret = f64to32(f) }
-func fcmp64c(f, g uint64, ret *int, retnan *bool) { *ret, *retnan = fcmp64(f, g) }
-func fintto64c(val int64, ret *uint64)            { *ret = fintto64(val) }
-func f64tointc(f uint64, ret *int64, retok *bool) { *ret, *retok = f64toint(f) }
+func fadd64c(f, g uint64, ret *uint64)              { *ret = fadd64(f, g) }
+func fsub64c(f, g uint64, ret *uint64)              { *ret = fsub64(f, g) }
+func fmul64c(f, g uint64, ret *uint64)              { *ret = fmul64(f, g) }
+func fdiv64c(f, g uint64, ret *uint64)              { *ret = fdiv64(f, g) }
+func fneg64c(f uint64, ret *uint64)                 { *ret = fneg64(f) }
+func f32to64c(f uint32, ret *uint64)                { *ret = f32to64(f) }
+func f64to32c(f uint64, ret *uint32)                { *ret = f64to32(f) }
+func fcmp64c(f, g uint64, ret *int32, retnan *bool) { *ret, *retnan = fcmp64(f, g) }
+func fintto64c(val int64, ret *uint64)              { *ret = fintto64(val) }
+func f64tointc(f uint64, ret *int64, retok *bool)   { *ret, *retok = f64toint(f) }

src/runtime/softfloat64_test.go

@@ -182,7 +182,7 @@ func hwcmp(f, g float64) (cmp int, isnan bool) {
 func testcmp(t *testing.T, f, g float64) {
 	hcmp, hisnan := hwcmp(f, g)
 	scmp, sisnan := Fcmp64(math.Float64bits(f), math.Float64bits(g))
-	if hcmp != scmp || hisnan != sisnan {
+	if int32(hcmp) != scmp || hisnan != sisnan {
 		err(t, "cmp(%g, %g) = sw %v, %v, hw %v, %v\n", f, g, scmp, sisnan, hcmp, hisnan)
 	}
 }

src/runtime/sqrt.go

@@ -141,7 +141,3 @@ func sqrt(x float64) float64 {
 	ix = q>>1 + uint64(exp-1+bias)<<shift // significand + biased exponent
 	return float64frombits(ix)
 }
-
-func sqrtC(f float64, r *float64) {
-	*r = sqrt(f)
-}