runtime: remove useless code around of EXCEPTION_BREAKPOINT

This is to simplify VEH handler before making
changes to fix issue 8006.

Update #8006

LGTM=adg, rsc
R=golang-codereviews, adg, rsc
CC=golang-codereviews
https://golang.org/cl/138630043

src/runtime/defs_windows.go

@@ -49,7 +49,6 @@ 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

src/runtime/defs_windows_386.h

@@ -22,7 +22,6 @@ 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,

src/runtime/defs_windows_amd64.h

@@ -22,7 +22,6 @@ 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,

src/runtime/os_windows_386.c

@@ -54,19 +54,6 @@ runtime·sighandler(ExceptionRecord *info, Context *r, G *gp)
 	if(r->Eip < (uint32)runtime·text || (uint32)runtime·etext < r->Eip)
 		return 0;
 
-	switch(info->ExceptionCode) {
-	case EXCEPTION_BREAKPOINT:
-		// 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.
-		//
-		// r->Eip--;	// because 8l generates 2 bytes for INT3
-		// return 0;
-		break;
-	}
-
 	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

src/runtime/os_windows_amd64.c

@@ -62,16 +62,6 @@ runtime·sighandler(ExceptionRecord *info, Context *r, G *gp)
 	if(r->Rip < (uint64)runtime·text || (uint64)runtime·etext < r->Rip)
 		return 0;
 
-	switch(info->ExceptionCode) {
-	case EXCEPTION_BREAKPOINT:
-		// 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)) {
 		// Make it look like a call to the signal func.
 		// Have to pass arguments out of band since