arm: bugfixes and syscall

- integer divide by zero raises panic
- float comparisons involving NaNs work
- syscall interface actually handles return
  values and errno correctly.

R=rsc, bradfitzpatrick
CC=golang-dev
https://golang.org/cl/1847047

src/cmd/5g/cgen.c

@@ -1044,7 +1044,16 @@ bgen(Node *n, int true, Prog *to)
 		cgen(nr, &n2);
 
 		gcmp(optoas(OCMP, nr->type), &n1, &n2);
+		if(isfloat[nl->type->etype]) {
+			p1 = gbranch(ABVS, nr->type);
 			patch(gbranch(a, nr->type), to);
+			if(n->op == ONE)
+				patch(p1, to);
+			else
+				patch(p1, pc);
+		} else {
+			patch(gbranch(a, nr->type), to);
+		}
 
 		regfree(&n1);
 		regfree(&n2);

src/pkg/runtime/arm/vlop.s

@@ -62,7 +62,7 @@ TEXT	save<>(SB), 7, $0
 	MOVW	20(FP), R(D)		/* denominator */
 	CMP	$0, R(D)
 	BNE	s1
-	SWI		 0
+	BL	panicdivide(SB)
 /*	  MOVW	-1(R(D)), R(TMP)	/* divide by zero fault */
 s1:	 RET
 

src/pkg/runtime/arm/vlrt.c

@@ -23,6 +23,9 @@
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 // THE SOFTWARE.
 
+// declared here to avoid include of runtime.h
+void	panicstring(char*);
+
 typedef unsigned long   ulong;
 typedef unsigned int    uint;
 typedef unsigned short  ushort;
@@ -31,6 +34,12 @@ typedef signed char     schar;
 
 #define SIGN(n) (1UL<<(n-1))
 
+void
+panicdivide(void)
+{
+	panicstring("integer divide by zero");
+}
+
 typedef struct  Vlong   Vlong;
 struct  Vlong
 {
@@ -190,7 +199,7 @@ dodiv(Vlong num, Vlong den, Vlong *q, Vlong *r)
 	 * get a divide by zero
 	 */
 	if(denlo==0 && denhi==0) {
-                numlo = numlo / denlo;
+		panicdivide();
 	}
 
 	/*

src/pkg/syscall/asm_linux_arm.s

@@ -17,9 +17,21 @@ TEXT	·Syscall(SB),7,$0
 	MOVW	12(SP), R1
 	MOVW	16(SP), R2
 	SWI		$0
+	MOVW	$0xfffff001, R1
+	CMP		R1, R0
+	BLS		ok
+	MOVW	$-1, R1
+	MOVW	R1, 20(SP)	// r1
+	MOVW	$0, R2
+	MOVW	R2, 24(SP)	// r2
+	RSB		$0, R0, R0
+	MOVW	R0, 28(SP)	// errno
+	BL		runtime·exitsyscall(SB)
+	RET
+ok:
 	MOVW	R0, 20(SP) // r1
-	MOVW	R1, 24(SP)	// r2
 	MOVW	$0, R0
+	MOVW	R0, 24(SP)	// r2
 	MOVW	R0, 28(SP)	// errno
 	BL		runtime·exitsyscall(SB)
 	RET
@@ -36,9 +48,21 @@ TEXT	·Syscall6(SB),7,$0
 	MOVW	24(SP), R4
 	MOVW	28(SP), R5
 	SWI		$0
+	MOVW	$0xfffff001, R1
+	CMP		R1, R0
+	BLS		ok6
+	MOVW	$-1, R1
+	MOVW	R1, 32(SP)	// r1
+	MOVW	$0, R2
+	MOVW	R2, 36(SP)	// r2
+	RSB		$0, R0, R0
+	MOVW	R0, 40(SP)	// errno
+	BL		runtime·exitsyscall(SB)
+	RET
+ok6:
 	MOVW	R0, 32(SP) // r1
-	MOVW	R1, 36(SP)	// r2
 	MOVW	$0, R0
+	MOVW	R0, 36(SP)	// r2
 	MOVW	R0, 40(SP)	// errno
 	BL		runtime·exitsyscall(SB)
 	RET
@@ -50,8 +74,19 @@ TEXT ·RawSyscall(SB),7,$0
 	MOVW	12(SP), R1
 	MOVW	16(SP), R2
 	SWI		$0
-	MOVW	R0, 20(SP)	// r1
-	MOVW	R1, 24(SP)	// r2
-	MOVW	$0, R0
+	MOVW	$0xfffff001, R1
+	CMP		R1, R0
+	BLS		ok1
+	MOVW	$-1, R1
+	MOVW	R1, 20(SP)	// r1
+	MOVW	$0, R2
+	MOVW	R2, 24(SP)	// r2
+	RSB		$0, R0, R0
+	MOVW	R0, 28(SP)	// errno
+	RET
+ok1:
+	MOVW	R0, 20(SP) // r1
+	MOVW	$0, R0
+	MOVW	R0, 24(SP)	// r2
 	MOVW	R0, 28(SP)	// errno
 	RET

test/arm-pass.txt

@@ -43,7 +43,7 @@
 ./env.go
 ./escape.go
 ./float_lit.go
-# ./floatcmp.go	# fail, BUG
+./floatcmp.go
 ./for.go
 ./func.go
 ./func1.go
@@ -116,7 +116,7 @@
 ./varerr.go
 ./varinit.go
 ./vectors.go
-# ./zerodivide.go	# fail, BUG
+./zerodivide.go
 ken/array.go
 ken/chan.go
 ken/chan1.go