runtime: handle all windows exception (second attempt)

includes undo of 22318cd31d7d and also:
- always use SetUnhandledExceptionFilter on windows-386;
- crash when receive EXCEPTION_BREAKPOINT in exception handler.

Fixes #8006.

LGTM=rsc
R=golang-codereviews, rsc
CC=golang-codereviews
https://golang.org/cl/155360043

9 files changed, 226 insertions, 72 deletions

diff --git a/src/runtime/defs_windows.go b/src/runtime/defs_windows.go
index cb0f54d8ab..7ce6797414 100644
--- a/src/runtime/defs_windows.go
+++ b/src/runtime/defs_windows.go
@@ -49,6 +49,7 @@ const (
 	CONTEXT_FULL    = C.CONTEXT_FULL
 
 	EXCEPTION_ACCESS_VIOLATION     = C.STATUS_ACCESS_VIOLATION
+	EXCEPTION_BREAKPOINT           = C.STATUS_BREAKPOINT
 	EXCEPTION_FLT_DENORMAL_OPERAND = C.STATUS_FLOAT_DENORMAL_OPERAND
 	EXCEPTION_FLT_DIVIDE_BY_ZERO   = C.STATUS_FLOAT_DIVIDE_BY_ZERO
 	EXCEPTION_FLT_INEXACT_RESULT   = C.STATUS_FLOAT_INEXACT_RESULT
@@ -59,6 +60,9 @@ const (
 
 	INFINITE     = C.INFINITE
 	WAIT_TIMEOUT = C.WAIT_TIMEOUT
+
+	EXCEPTION_CONTINUE_EXECUTION = C.EXCEPTION_CONTINUE_EXECUTION
+	EXCEPTION_CONTINUE_SEARCH    = C.EXCEPTION_CONTINUE_SEARCH
 )
 
 type SystemInfo C.SYSTEM_INFO
diff --git a/src/runtime/defs_windows_386.h b/src/runtime/defs_windows_386.h
index 295e422c6b..2317c04f65 100644
--- a/src/runtime/defs_windows_386.h
+++ b/src/runtime/defs_windows_386.h
@@ -22,6 +22,7 @@ enum {
 	CONTEXT_FULL	= 0x10007,
 
 	EXCEPTION_ACCESS_VIOLATION	= 0xc0000005,
+	EXCEPTION_BREAKPOINT		= 0x80000003,
 	EXCEPTION_FLT_DENORMAL_OPERAND	= 0xc000008d,
 	EXCEPTION_FLT_DIVIDE_BY_ZERO	= 0xc000008e,
 	EXCEPTION_FLT_INEXACT_RESULT	= 0xc000008f,
@@ -32,6 +33,9 @@ enum {
 
 	INFINITE	= 0xffffffff,
 	WAIT_TIMEOUT	= 0x102,
+
+	EXCEPTION_CONTINUE_EXECUTION	= -0x1,
+	EXCEPTION_CONTINUE_SEARCH	= 0x0,
 };
 
 typedef struct SystemInfo SystemInfo;
diff --git a/src/runtime/defs_windows_amd64.h b/src/runtime/defs_windows_amd64.h
index 2516c84128..7f37a7a8c3 100644
--- a/src/runtime/defs_windows_amd64.h
+++ b/src/runtime/defs_windows_amd64.h
@@ -22,6 +22,7 @@ enum {
 	CONTEXT_FULL	= 0x10000b,
 
 	EXCEPTION_ACCESS_VIOLATION	= 0xc0000005,
+	EXCEPTION_BREAKPOINT		= 0x80000003,
 	EXCEPTION_FLT_DENORMAL_OPERAND	= 0xc000008d,
 	EXCEPTION_FLT_DIVIDE_BY_ZERO	= 0xc000008e,
 	EXCEPTION_FLT_INEXACT_RESULT	= 0xc000008f,
@@ -32,6 +33,9 @@ enum {
 
 	INFINITE	= 0xffffffff,
 	WAIT_TIMEOUT	= 0x102,
+
+	EXCEPTION_CONTINUE_EXECUTION	= -0x1,
+	EXCEPTION_CONTINUE_SEARCH	= 0x0,
 };
 
 typedef struct SystemInfo SystemInfo;
diff --git a/src/runtime/os_windows.c b/src/runtime/os_windows.c
index 6337dde2af..b8b8eda5f3 100644
--- a/src/runtime/os_windows.c
+++ b/src/runtime/os_windows.c
@@ -34,6 +34,7 @@
 #pragma dynimport runtime·SetEvent SetEvent "kernel32.dll"
 #pragma dynimport runtime·SetProcessPriorityBoost SetProcessPriorityBoost "kernel32.dll"
 #pragma dynimport runtime·SetThreadPriority SetThreadPriority "kernel32.dll"
+#pragma dynimport runtime·SetUnhandledExceptionFilter SetUnhandledExceptionFilter "kernel32.dll"
 #pragma dynimport runtime·SetWaitableTimer SetWaitableTimer "kernel32.dll"
 #pragma dynimport runtime·Sleep Sleep "kernel32.dll"
 #pragma dynimport runtime·SuspendThread SuspendThread "kernel32.dll"
@@ -65,6 +66,7 @@ extern void *runtime·SetConsoleCtrlHandler;
 extern void *runtime·SetEvent;
 extern void *runtime·SetProcessPriorityBoost;
 extern void *runtime·SetThreadPriority;
+extern void *runtime·SetUnhandledExceptionFilter;
 extern void *runtime·SetWaitableTimer;
 extern void *runtime·Sleep;
 extern void *runtime·SuspendThread;
@@ -77,7 +79,9 @@ void *runtime·GetQueuedCompletionStatusEx;
 
 extern uintptr runtime·externalthreadhandlerp;
 void runtime·externalthreadhandler(void);
-void runtime·sigtramp(void);
+void runtime·exceptiontramp(void);
+void runtime·firstcontinuetramp(void);
+void runtime·lastcontinuetramp(void);
 
 #pragma textflag NOSPLIT
 uintptr
@@ -106,12 +110,30 @@ void
 runtime·osinit(void)
 {
 	void *kernel32;
+	void *addVectoredContinueHandler;
+
+	kernel32 = runtime·stdcall1(runtime·LoadLibraryA, (uintptr)"kernel32.dll");
 
 	runtime·externalthreadhandlerp = (uintptr)runtime·externalthreadhandler;
 
-	runtime·stdcall2(runtime·AddVectoredExceptionHandler, 1, (uintptr)runtime·sigtramp);
+	runtime·stdcall2(runtime·AddVectoredExceptionHandler, 1, (uintptr)runtime·exceptiontramp);
+	addVectoredContinueHandler = nil;
+	if(kernel32 != nil)
+		addVectoredContinueHandler = runtime·stdcall2(runtime·GetProcAddress, (uintptr)kernel32, (uintptr)"AddVectoredContinueHandler");
+	if(addVectoredContinueHandler == nil || sizeof(void*) == 4) {
+		// use SetUnhandledExceptionFilter for windows-386 or
+		// if VectoredContinueHandler is unavailable.
+		// note: SetUnhandledExceptionFilter handler won't be called, if debugging.
+		runtime·stdcall1(runtime·SetUnhandledExceptionFilter, (uintptr)runtime·lastcontinuetramp);
+	} else {
+		runtime·stdcall2(addVectoredContinueHandler, 1, (uintptr)runtime·firstcontinuetramp);
+		runtime·stdcall2(addVectoredContinueHandler, 0, (uintptr)runtime·lastcontinuetramp);
+	}
+
 	runtime·stdcall2(runtime·SetConsoleCtrlHandler, (uintptr)runtime·ctrlhandler, 1);
+
 	runtime·stdcall1(runtime·timeBeginPeriod, 1);
+
 	runtime·ncpu = getproccount();
 	
 	// Windows dynamic priority boosting assumes that a process has different types
@@ -120,7 +142,6 @@ runtime·osinit(void)
 	// In such context dynamic priority boosting does nothing but harm, so we turn it off.
 	runtime·stdcall2(runtime·SetProcessPriorityBoost, -1, 1);
 
-	kernel32 = runtime·stdcall1(runtime·LoadLibraryA, (uintptr)"kernel32.dll");
 	if(kernel32 != nil) {
 		runtime·GetQueuedCompletionStatusEx = runtime·stdcall2(runtime·GetProcAddress, (uintptr)kernel32, (uintptr)"GetQueuedCompletionStatusEx");
 	}
@@ -467,6 +488,7 @@ runtime·issigpanic(uint32 code)
 	case EXCEPTION_FLT_INEXACT_RESULT:
 	case EXCEPTION_FLT_OVERFLOW:
 	case EXCEPTION_FLT_UNDERFLOW:
+	case EXCEPTION_BREAKPOINT:
 		return 1;
 	}
 	return 0;
@@ -475,10 +497,14 @@ runtime·issigpanic(uint32 code)
 void
 runtime·initsig(void)
 {
-	// following line keeps sigtramp alive at link stage
+	// following line keeps these functions alive at link stage
 	// if there's a better way please write it here
-	void *p = runtime·sigtramp;
-	USED(p);
+	void *e = runtime·exceptiontramp;
+	void *f = runtime·firstcontinuetramp;
+	void *l = runtime·lastcontinuetramp;
+	USED(e);
+	USED(f);
+	USED(l);
 }
 
 uint32
diff --git a/src/runtime/os_windows_386.c b/src/runtime/os_windows_386.c
index e2ae8db277..213582799b 100644
--- a/src/runtime/os_windows_386.c
+++ b/src/runtime/os_windows_386.c
@@ -24,45 +24,63 @@ runtime·dumpregs(Context *r)
 	runtime·printf("gs      %x\n", r->SegGs);
 }
 
-// Called by sigtramp from Windows VEH handler.
-// Return value signals whether the exception has been handled (-1)
-// or should be made available to other handlers in the chain (0).
-uint32
-runtime·sighandler(ExceptionRecord *info, Context *r, G *gp)
+bool
+runtime·isgoexception(ExceptionRecord *info, Context *r)
 {
-	bool crash;
-	uintptr *sp;
 	extern byte runtime·text[], runtime·etext[];
 
 	// Only handle exception if executing instructions in Go binary
 	// (not Windows library code). 
 	if(r->Eip < (uint32)runtime·text || (uint32)runtime·etext < r->Eip)
-		return 0;
+		return false;
+
+	if(!runtime·issigpanic(info->ExceptionCode))
+		return false;
+
+	return true;
+}
+
+// Called by sigtramp from Windows VEH handler.
+// Return value signals whether the exception has been handled (EXCEPTION_CONTINUE_EXECUTION)
+// or should be made available to other handlers in the chain (EXCEPTION_CONTINUE_SEARCH).
+uint32
+runtime·exceptionhandler(ExceptionRecord *info, Context *r, G *gp)
+{
+	uintptr *sp;
 
-	if(gp != nil && runtime·issigpanic(info->ExceptionCode)) {
-		// Make it look like a call to the signal func.
-		// Have to pass arguments out of band since
-		// augmenting the stack frame would break
-		// the unwinding code.
-		gp->sig = info->ExceptionCode;
-		gp->sigcode0 = info->ExceptionInformation[0];
-		gp->sigcode1 = info->ExceptionInformation[1];
-		gp->sigpc = r->Eip;
+	if(!runtime·isgoexception(info, r))
+		return EXCEPTION_CONTINUE_SEARCH;
 
-		// Only push runtime·sigpanic if r->eip != 0.
-		// If r->eip == 0, probably panicked because of a
-		// call to a nil func.  Not pushing that onto sp will
-		// make the trace look like a call to runtime·sigpanic instead.
-		// (Otherwise the trace will end at runtime·sigpanic and we
-		// won't get to see who faulted.)
-		if(r->Eip != 0) {
-			sp = (uintptr*)r->Esp;
-			*--sp = r->Eip;
-			r->Esp = (uintptr)sp;
-		}
-		r->Eip = (uintptr)runtime·sigpanic;
-		return -1;
+	// Make it look like a call to the signal func.
+	// Have to pass arguments out of band since
+	// augmenting the stack frame would break
+	// the unwinding code.
+	gp->sig = info->ExceptionCode;
+	gp->sigcode0 = info->ExceptionInformation[0];
+	gp->sigcode1 = info->ExceptionInformation[1];
+	gp->sigpc = r->Eip;
+
+	// Only push runtime·sigpanic if r->eip != 0.
+	// If r->eip == 0, probably panicked because of a
+	// call to a nil func.  Not pushing that onto sp will
+	// make the trace look like a call to runtime·sigpanic instead.
+	// (Otherwise the trace will end at runtime·sigpanic and we
+	// won't get to see who faulted.)
+	if(r->Eip != 0) {
+		sp = (uintptr*)r->Esp;
+		*--sp = r->Eip;
+		r->Esp = (uintptr)sp;
 	}
+	r->Eip = (uintptr)runtime·sigpanic;
+	return EXCEPTION_CONTINUE_EXECUTION;
+}
+
+// lastcontinuehandler is reached, because runtime cannot handle
+// current exception. lastcontinuehandler will print crash info and exit.
+uint32
+runtime·lastcontinuehandler(ExceptionRecord *info, Context *r, G *gp)
+{
+	bool crash;
 
 	if(runtime·panicking)	// traceback already printed
 		runtime·exit(2);
@@ -88,7 +106,7 @@ runtime·sighandler(ExceptionRecord *info, Context *r, G *gp)
 		runtime·crash();
 
 	runtime·exit(2);
-	return -1; // not reached
+	return 0; // not reached
 }
 
 void
diff --git a/src/runtime/os_windows_amd64.c b/src/runtime/os_windows_amd64.c
index 261880d450..b96cf70d1e 100644
--- a/src/runtime/os_windows_amd64.c
+++ b/src/runtime/os_windows_amd64.c
@@ -32,45 +32,76 @@ runtime·dumpregs(Context *r)
 	runtime·printf("gs      %X\n", (uint64)r->SegGs);
 }
 
-// Called by sigtramp from Windows VEH handler.
-// Return value signals whether the exception has been handled (-1)
-// or should be made available to other handlers in the chain (0).
-uint32
-runtime·sighandler(ExceptionRecord *info, Context *r, G *gp)
+bool
+runtime·isgoexception(ExceptionRecord *info, Context *r)
 {
-	bool crash;
-	uintptr *sp;
 	extern byte runtime·text[], runtime·etext[];
 
 	// Only handle exception if executing instructions in Go binary
 	// (not Windows library code). 
 	if(r->Rip < (uint64)runtime·text || (uint64)runtime·etext < r->Rip)
-		return 0;
+		return false;
+
+	if(!runtime·issigpanic(info->ExceptionCode))
+		return false;
+
+	return true;
+}
+
+// Called by sigtramp from Windows VEH handler.
+// Return value signals whether the exception has been handled (EXCEPTION_CONTINUE_EXECUTION)
+// or should be made available to other handlers in the chain (EXCEPTION_CONTINUE_SEARCH).
+uint32
+runtime·exceptionhandler(ExceptionRecord *info, Context *r, G *gp)
+{
+	uintptr *sp;
+
+	if(!runtime·isgoexception(info, r))
+		return EXCEPTION_CONTINUE_SEARCH;
 
-	if(gp != nil && runtime·issigpanic(info->ExceptionCode)) {
-		// Make it look like a call to the signal func.
-		// Have to pass arguments out of band since
-		// augmenting the stack frame would break
-		// the unwinding code.
-		gp->sig = info->ExceptionCode;
-		gp->sigcode0 = info->ExceptionInformation[0];
-		gp->sigcode1 = info->ExceptionInformation[1];
-		gp->sigpc = r->Rip;
+	// Make it look like a call to the signal func.
+	// Have to pass arguments out of band since
+	// augmenting the stack frame would break
+	// the unwinding code.
+	gp->sig = info->ExceptionCode;
+	gp->sigcode0 = info->ExceptionInformation[0];
+	gp->sigcode1 = info->ExceptionInformation[1];
+	gp->sigpc = r->Rip;
 
-		// Only push runtime·sigpanic if r->rip != 0.
-		// If r->rip == 0, probably panicked because of a
-		// call to a nil func.  Not pushing that onto sp will
-		// make the trace look like a call to runtime·sigpanic instead.
-		// (Otherwise the trace will end at runtime·sigpanic and we
-		// won't get to see who faulted.)
-		if(r->Rip != 0) {
-			sp = (uintptr*)r->Rsp;
-			*--sp = r->Rip;
-			r->Rsp = (uintptr)sp;
-		}
-		r->Rip = (uintptr)runtime·sigpanic;
-		return -1;
+	// Only push runtime·sigpanic if r->rip != 0.
+	// If r->rip == 0, probably panicked because of a
+	// call to a nil func.  Not pushing that onto sp will
+	// make the trace look like a call to runtime·sigpanic instead.
+	// (Otherwise the trace will end at runtime·sigpanic and we
+	// won't get to see who faulted.)
+	if(r->Rip != 0) {
+		sp = (uintptr*)r->Rsp;
+		*--sp = r->Rip;
+		r->Rsp = (uintptr)sp;
 	}
+	r->Rip = (uintptr)runtime·sigpanic;
+	return EXCEPTION_CONTINUE_EXECUTION;
+}
+
+// It seems Windows searches ContinueHandler's list even
+// if ExceptionHandler returns EXCEPTION_CONTINUE_EXECUTION.
+// firstcontinuehandler will stop that search,
+// if exceptionhandler did the same earlier.
+uint32
+runtime·firstcontinuehandler(ExceptionRecord *info, Context *r, G *gp)
+{
+	USED(gp);
+	if(!runtime·isgoexception(info, r))
+		return EXCEPTION_CONTINUE_SEARCH;
+	return EXCEPTION_CONTINUE_EXECUTION;
+}
+
+// lastcontinuehandler is reached, because runtime cannot handle
+// current exception. lastcontinuehandler will print crash info and exit.
+uint32
+runtime·lastcontinuehandler(ExceptionRecord *info, Context *r, G *gp)
+{
+	bool crash;
 
 	if(runtime·panicking)	// traceback already printed
 		runtime·exit(2);
@@ -97,7 +128,7 @@ runtime·sighandler(ExceptionRecord *info, Context *r, G *gp)
 		runtime·crash();
 
 	runtime·exit(2);
-	return -1; // not reached
+	return 0; // not reached
 }
 
 void
diff --git a/src/runtime/sys_windows_386.s b/src/runtime/sys_windows_386.s
index 1bf4d062ac..932fe9dd24 100644
--- a/src/runtime/sys_windows_386.s
+++ b/src/runtime/sys_windows_386.s
@@ -73,6 +73,7 @@ TEXT runtime·setlasterror(SB),NOSPLIT,$0
 // Called by Windows as a Vectored Exception Handler (VEH).
 // First argument is pointer to struct containing
 // exception record and context pointers.
+// Handler function is stored in AX.
 // Return 0 for 'not handled', -1 for handled.
 TEXT runtime·sigtramp(SB),NOSPLIT,$0-0
 	MOVL	ptrs+0(FP), CX
@@ -84,6 +85,8 @@ TEXT runtime·sigtramp(SB),NOSPLIT,$0-0
 	MOVL	SI, 20(SP)
 	MOVL	DI, 24(SP)
 
+	MOVL	AX, SI	// save handler address
+
 	// find g
 	get_tls(DX)
 	CMPL	DX, $0
@@ -123,11 +126,10 @@ TEXT runtime·sigtramp(SB),NOSPLIT,$0-0
 sigtramp_g0:
 	MOVL	0(CX), BX // ExceptionRecord*
 	MOVL	4(CX), CX // Context*
-	// call sighandler(ExceptionRecord*, Context*, G*)
 	MOVL	BX, 0(SP)
 	MOVL	CX, 4(SP)
 	MOVL	DX, 8(SP)
-	CALL	runtime·sighandler(SB)
+	CALL	SI	// call handler
 	// AX is set to report result back to Windows
 	MOVL	12(SP), AX
 
@@ -149,6 +151,18 @@ done:
 	// RET 4 (return and pop 4 bytes parameters)
 	BYTE $0xC2; WORD $4
 	RET // unreached; make assembler happy
+ 
+TEXT runtime·exceptiontramp(SB),NOSPLIT,$0
+	MOVL	$runtime·exceptionhandler(SB), AX
+	JMP	runtime·sigtramp(SB)
+
+TEXT runtime·firstcontinuetramp(SB),NOSPLIT,$0-0
+	// is never called
+	INT	$3
+
+TEXT runtime·lastcontinuetramp(SB),NOSPLIT,$0-0
+	MOVL	$runtime·lastcontinuehandler(SB), AX
+	JMP	runtime·sigtramp(SB)
 
 TEXT runtime·ctrlhandler(SB),NOSPLIT,$0
 	PUSHL	$runtime·ctrlhandler1(SB)
diff --git a/src/runtime/sys_windows_amd64.s b/src/runtime/sys_windows_amd64.s
index 05750398ea..e6190ce684 100644
--- a/src/runtime/sys_windows_amd64.s
+++ b/src/runtime/sys_windows_amd64.s
@@ -99,6 +99,7 @@ TEXT runtime·setlasterror(SB),NOSPLIT,$0
 // Called by Windows as a Vectored Exception Handler (VEH).
 // First argument is pointer to struct containing
 // exception record and context pointers.
+// Handler function is stored in AX.
 // Return 0 for 'not handled', -1 for handled.
 TEXT runtime·sigtramp(SB),NOSPLIT,$0-0
 	// CX: PEXCEPTION_POINTERS ExceptionInfo
@@ -116,6 +117,8 @@ TEXT runtime·sigtramp(SB),NOSPLIT,$0-0
 	MOVQ	R14, 32(SP)
 	MOVQ	R15, 88(SP)
 
+	MOVQ	AX, R15	// save handler address
+
 	// find g
 	get_tls(DX)
 	CMPQ	DX, $0
@@ -157,11 +160,10 @@ TEXT runtime·sigtramp(SB),NOSPLIT,$0-0
 sigtramp_g0:
 	MOVQ	0(CX), BX // ExceptionRecord*
 	MOVQ	8(CX), CX // Context*
-	// call sighandler(ExceptionRecord*, Context*, G*)
 	MOVQ	BX, 0(SP)
 	MOVQ	CX, 8(SP)
 	MOVQ	DX, 16(SP)
-	CALL	runtime·sighandler(SB)
+	CALL	R15	// call handler
 	// AX is set to report result back to Windows
 	MOVL	24(SP), AX
 
@@ -187,6 +189,18 @@ done:
 
 	RET
 
+TEXT runtime·exceptiontramp(SB),NOSPLIT,$0
+	MOVQ	$runtime·exceptionhandler(SB), AX
+	JMP	runtime·sigtramp(SB)
+
+TEXT runtime·firstcontinuetramp(SB),NOSPLIT,$0-0
+	MOVQ	$runtime·firstcontinuehandler(SB), AX
+	JMP	runtime·sigtramp(SB)
+
+TEXT runtime·lastcontinuetramp(SB),NOSPLIT,$0-0
+	MOVQ	$runtime·lastcontinuehandler(SB), AX
+	JMP	runtime·sigtramp(SB)
+
 TEXT runtime·ctrlhandler(SB),NOSPLIT,$8
 	MOVQ	CX, 16(SP)		// spill
 	MOVQ	$runtime·ctrlhandler1(SB), CX
diff --git a/src/runtime/syscall_windows_test.go b/src/runtime/syscall_windows_test.go
index 9ed016ccc8..ce8a9ec1ba 100644
--- a/src/runtime/syscall_windows_test.go
+++ b/src/runtime/syscall_windows_test.go
@@ -494,3 +494,42 @@ func TestOutputDebugString(t *testing.T) {
 	p := syscall.StringToUTF16Ptr("testing OutputDebugString")
 	d.Proc("OutputDebugStringW").Call(uintptr(unsafe.Pointer(p)))
 }
+
+func TestRaiseException(t *testing.T) {
+	o := executeTest(t, raiseExceptionSource, nil)
+	if strings.Contains(o, "RaiseException should not return") {
+		t.Fatalf("RaiseException did not crash program: %v", o)
+	}
+	if !strings.Contains(o, "Exception 0xbad") {
+		t.Fatalf("No stack trace: %v", o)
+	}
+}
+
+const raiseExceptionSource = `
+package main
+import "syscall"
+func main() {
+	const EXCEPTION_NONCONTINUABLE = 1
+	mod := syscall.MustLoadDLL("kernel32.dll")
+	proc := mod.MustFindProc("RaiseException")
+	proc.Call(0xbad, EXCEPTION_NONCONTINUABLE, 0, 0)
+	println("RaiseException should not return")
+}
+`
+
+func TestZeroDivisionException(t *testing.T) {
+	o := executeTest(t, zeroDivisionExceptionSource, nil)
+	if !strings.Contains(o, "panic: runtime error: integer divide by zero") {
+		t.Fatalf("No stack trace: %v", o)
+	}
+}
+
+const zeroDivisionExceptionSource = `
+package main
+func main() {
+	x := 1
+	y := 0
+	z := x / y
+	println(z)
+}
+`