runtime: use VEH for windows/amd64 exception handling

Fixes windows/amd64 build.

LGTM=rsc
R=golang-codereviews, rsc
CC=golang-codereviews
https://golang.org/cl/79470046

src/cmd/ld/pe.c

@@ -529,49 +529,6 @@ addpersrc(void)
 	dd[IMAGE_DIRECTORY_ENTRY_RESOURCE].Size = h->VirtualSize;
 }
 
-static void
-addexcept(IMAGE_SECTION_HEADER *text)
-{
-	IMAGE_SECTION_HEADER *pdata, *xdata;
-	vlong startoff;
-	uvlong n;
-	LSym *sym;
-
-	USED(text);
-	if(thechar != '6')
-		return;
-
-	// write unwind info
-	sym = linklookup(ctxt, "runtime.sigtramp", 0);
-	startoff = cpos();
-	lputl(9);	// version=1, flags=UNW_FLAG_EHANDLER, rest 0
-	lputl(sym->value - PEBASE);
-	lputl(0);
-
-	n = cpos() - startoff;
-	xdata = addpesection(".xdata", n, n);
-	xdata->Characteristics = IMAGE_SCN_MEM_READ|
-		IMAGE_SCN_CNT_INITIALIZED_DATA;
-	chksectoff(xdata, startoff);
-	strnput("", xdata->SizeOfRawData - n);
-
-	// write a function table entry for the whole text segment
-	startoff = cpos();
-	lputl(text->VirtualAddress);
-	lputl(text->VirtualAddress + text->VirtualSize);
-	lputl(xdata->VirtualAddress);
-
-	n = cpos() - startoff;
-	pdata = addpesection(".pdata", n, n);
-	pdata->Characteristics = IMAGE_SCN_MEM_READ|
-		IMAGE_SCN_CNT_INITIALIZED_DATA;
-	chksectoff(pdata, startoff);
-	strnput("", pdata->SizeOfRawData - n);
-
-	dd[IMAGE_DIRECTORY_ENTRY_EXCEPTION].VirtualAddress = pdata->VirtualAddress;
-	dd[IMAGE_DIRECTORY_ENTRY_EXCEPTION].Size = pdata->VirtualSize;
-}
-
 void
 asmbpe(void)
 {
@@ -609,7 +566,6 @@ asmbpe(void)
 	addexports();
 	addsymtable();
 	addpersrc();
-	addexcept(t);
 
 	fh.NumberOfSections = nsect;
 	fh.TimeDateStamp = time(0);

src/pkg/runtime/os_windows.c

@@ -248,15 +248,12 @@ runtime·minit(void)
 		(uintptr)-1, (uintptr)-2, (uintptr)-1, &thandle,
 		(uintptr)0, (uintptr)0, (uintptr)DUPLICATE_SAME_ACCESS);
 	runtime·atomicstorep(&m->thread, thandle);
-
-	runtime·install_exception_handler();
 }
 
 // Called from dropm to undo the effect of an minit.
 void
 runtime·unminit(void)
 {
-	runtime·remove_exception_handler();
 }
 
 #pragma textflag NOSPLIT

src/pkg/runtime/os_windows_amd64.c

@@ -32,6 +32,11 @@ runtime·dumpregs(Context *r)
 	runtime·printf("gs      %X\n", (uint64)r->SegGs);
 }
 
+#define DBG_PRINTEXCEPTION_C 0x40010006
+
+// 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)
 {
@@ -39,8 +44,25 @@ runtime·sighandler(ExceptionRecord *info, Context *r, G *gp)
 	uintptr *sp;
 
 	switch(info->ExceptionCode) {
+	case DBG_PRINTEXCEPTION_C:
+		// This exception is intended to be caught by debuggers.
+		// There is a not-very-informational message like
+		// "Invalid parameter passed to C runtime function"
+		// sitting at info->ExceptionInformation[0] (a wchar_t*),
+		// with length info->ExceptionInformation[1].
+		// The default behavior is to ignore this exception,
+		// but somehow returning 0 here (meaning keep going)
+		// makes the program crash instead. Maybe Windows has no
+		// other handler registered? In any event, ignore it.
+		return -1;
+
 	case EXCEPTION_BREAKPOINT:
-		return 1;
+		// It is unclear whether this is needed, unclear whether it
+		// would work, and unclear how to test it. Leave out for now.
+		// This only handles breakpoint instructions written in the
+		// assembly sources, not breakpoints set by a debugger, and
+		// there are very few of the former.
+		break;
 	}
 
 	if(gp != nil && runtime·issigpanic(info->ExceptionCode)) {
@@ -65,15 +87,16 @@ runtime·sighandler(ExceptionRecord *info, Context *r, G *gp)
 			r->Rsp = (uintptr)sp;
 		}
 		r->Rip = (uintptr)runtime·sigpanic;
-		return 0;
+		return -1;
 	}
 
 	if(runtime·panicking)	// traceback already printed
 		runtime·exit(2);
 	runtime·panicking = 1;
 
-	runtime·printf("Exception %x %p %p\n", info->ExceptionCode,
-		info->ExceptionInformation[0], info->ExceptionInformation[1]);
+	runtime·printf("Exception %x %p %p %p\n", info->ExceptionCode,
+		info->ExceptionInformation[0], info->ExceptionInformation[1], r->Rip);
+
 
 	runtime·printf("PC=%X\n", r->Rip);
 	if(m->lockedg != nil && m->ncgo > 0 && gp == m->g0) {
@@ -92,7 +115,7 @@ runtime·sighandler(ExceptionRecord *info, Context *r, G *gp)
 		runtime·crash();
 
 	runtime·exit(2);
-	return 0;
+	return -1; // not reached
 }
 
 void

src/pkg/runtime/sys_windows_386.s

@@ -313,14 +313,6 @@ TEXT runtime·setldt(SB),NOSPLIT,$0
 	MOVL	CX, 0x14(FS)
 	RET
 
-// void install_exception_handler()
-TEXT runtime·install_exception_handler(SB),NOSPLIT,$0
-	RET
-
-// void remove_exception_handler()
-TEXT runtime·remove_exception_handler(SB),NOSPLIT,$0
-	RET
-
 // Sleep duration is in 100ns units.
 TEXT runtime·usleep1(SB),NOSPLIT,$0
 	MOVL	duration+0(FP), BX

src/pkg/runtime/sys_windows_amd64.s

@@ -95,49 +95,55 @@ TEXT runtime·setlasterror(SB),NOSPLIT,$0
 	MOVL	AX, 0x68(CX)
 	RET
 
-TEXT runtime·sigtramp(SB),NOSPLIT,$0
-	// CX: exception record
-	// R8: context
+// Called by Windows as a Vectored Exception Handler (VEH).
+// First argument is pointer to struct containing
+// exception record and context pointers.
+// Return 0 for 'not handled', -1 for handled.
+TEXT runtime·sigtramp(SB),NOSPLIT,$0-0
+	// CX: PEXCEPTION_POINTERS ExceptionInfo
 
-	// unwinding?
-	TESTL	$6, 4(CX)		// exception flags
-	MOVL	$1, AX
-	JNZ	sigdone
+	// DI SI BP BX R12 R13 R14 R15 registers and DF flag are preserved
+	// as required by windows callback convention.
+	PUSHFQ
+	SUBQ	$88, SP
+	MOVQ	DI, 80(SP)
+	MOVQ	SI, 72(SP)
+	MOVQ	BP, 64(SP)
+	MOVQ	BX, 56(SP)
+	MOVQ	R12, 48(SP)
+	MOVQ	R13, 40(SP)
+	MOVQ	R14, 32(SP)
+	MOVQ	R15, 24(SP)
 
-	// copy arguments for call to sighandler.
+	MOVQ	0(CX), BX // ExceptionRecord*
+	MOVQ	8(CX), CX // Context*
 
-	// Stack adjustment is here to hide from 6l,
-	// which doesn't understand that sigtramp
-	// runs on essentially unlimited stack.
-	SUBQ	$56, SP
-	MOVQ	CX, 0(SP)
-	MOVQ	R8, 8(SP)
-
-	get_tls(CX)
-
-	// check that m exists
-	MOVQ	m(CX), AX
+	// fetch g
+	get_tls(DX)
+	MOVQ	m(DX), AX
 	CMPQ	AX, $0
 	JNE	2(PC)
 	CALL	runtime·badsignal2(SB)
-
-	MOVQ	g(CX), CX
-	MOVQ	CX, 16(SP)
-
-	MOVQ	BX, 24(SP)
-	MOVQ	BP, 32(SP)
-	MOVQ	SI, 40(SP)
-	MOVQ	DI, 48(SP)
-
+	MOVQ	g(DX), DX
+	// call sighandler(ExceptionRecord*, Context*, G*)
+	MOVQ	BX, 0(SP)
+	MOVQ	CX, 8(SP)
+	MOVQ	DX, 16(SP)
 	CALL	runtime·sighandler(SB)
+	// AX is set to report result back to Windows
 
-	MOVQ	24(SP), BX
-	MOVQ	32(SP), BP
-	MOVQ	40(SP), SI
-	MOVQ	48(SP), DI
-	ADDQ	$56, SP
+	// restore registers as required for windows callback
+	MOVQ	24(SP), R15
+	MOVQ	32(SP), R14
+	MOVQ	40(SP), R13
+	MOVQ	48(SP), R12
+	MOVQ	56(SP), BX
+	MOVQ	64(SP), BP
+	MOVQ	72(SP), SI
+	MOVQ	80(SP), DI
+	ADDQ	$88, SP
+	POPFQ
 
-sigdone:
 	RET
 
 TEXT runtime·ctrlhandler(SB),NOSPLIT,$8
@@ -277,13 +283,6 @@ TEXT runtime·callbackasm1(SB),NOSPLIT,$0
 	POPQ	-8(CX)(DX*1)      // restore bytes just after the args
 	RET
 
-TEXT runtime·setstacklimits(SB),NOSPLIT,$0
-	MOVQ	0x30(GS), CX
-	MOVQ	$0, 0x10(CX)
-	MOVQ	$0xffffffffffff, AX
-	MOVQ	AX, 0x08(CX)
-	RET
-
 // uint32 tstart_stdcall(M *newm);
 TEXT runtime·tstart_stdcall(SB),NOSPLIT,$0
 	// CX contains first arg newm
@@ -315,14 +314,6 @@ TEXT runtime·settls(SB),NOSPLIT,$0
 	MOVQ	DI, 0x28(GS)
 	RET
 
-// void install_exception_handler()
-TEXT runtime·install_exception_handler(SB),NOSPLIT,$0
-	CALL	runtime·setstacklimits(SB)
-	RET
-
-TEXT runtime·remove_exception_handler(SB),NOSPLIT,$0
-	RET
-
 // Sleep duration is in 100ns units.
 TEXT runtime·usleep1(SB),NOSPLIT,$0
 	MOVL	duration+0(FP), BX