runtime: simplify and comment some windows code
Change-Id: I5cedd9e53f4e020aea74d498d0db88d79a95260c
Reviewed-on: https://go-review.googlesource.com/2718
Reviewed-by: Minux Ma <minux@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
diff --git a/src/runtime/os1_windows.go b/src/runtime/os1_windows.go
index 5be916c..8d469aa 100644
--- a/src/runtime/os1_windows.go
+++ b/src/runtime/os1_windows.go
@@ -42,6 +42,9 @@
//go:cgo_import_dynamic runtime._timeBeginPeriod timeBeginPeriod "winmm.dll"
var (
+ // Following syscalls are available on every Windows PC.
+ // All these variables are set by the Windows executable
+ // loader before the Go program starts.
_AddVectoredExceptionHandler,
_CloseHandle,
_CreateEventA,
@@ -74,9 +77,29 @@
_WaitForSingleObject,
_WriteFile,
_timeBeginPeriod stdFunction
+
+ // Following syscalls are only available on some Windows PCs.
+ // We will load syscalls, if available, before using them.
+ _AddVectoredContinueHandler,
+ _GetQueuedCompletionStatusEx stdFunction
)
-var _GetQueuedCompletionStatusEx stdFunction
+func loadOptionalSyscalls() {
+ var buf [50]byte // large enough for longest string
+ strtoptr := func(s string) uintptr {
+ buf[copy(buf[:], s)] = 0 // nil-terminated for OS
+ return uintptr(noescape(unsafe.Pointer(&buf[0])))
+ }
+ l := stdcall1(_LoadLibraryA, strtoptr("kernel32.dll"))
+ findfunc := func(name string) stdFunction {
+ f := stdcall2(_GetProcAddress, l, strtoptr(name))
+ return stdFunction(unsafe.Pointer(f))
+ }
+ if l != 0 {
+ _AddVectoredContinueHandler = findfunc("AddVectoredContinueHandler")
+ _GetQueuedCompletionStatusEx = findfunc("GetQueuedCompletionStatusEx")
+ }
+}
// in sys_windows_386.s and sys_windows_amd64.s
func externalthreadhandler()
@@ -117,34 +140,24 @@
stdcall1(_SetErrorMode, uintptr(errormode)|SEM_FAILCRITICALERRORS|SEM_NOGPFAULTERRORBOX|SEM_NOOPENFILEERRORBOX)
}
-var (
- kernel32Name = []byte("kernel32.dll\x00")
- addVectoredContinueHandlerName = []byte("AddVectoredContinueHandler\x00")
- getQueuedCompletionStatusExName = []byte("GetQueuedCompletionStatusEx\x00")
-)
-
func osinit() {
setBadSignalMsg()
- kernel32 := stdcall1(_LoadLibraryA, uintptr(unsafe.Pointer(&kernel32Name[0])))
+ loadOptionalSyscalls()
disableWER()
externalthreadhandlerp = funcPC(externalthreadhandler)
stdcall2(_AddVectoredExceptionHandler, 1, funcPC(exceptiontramp))
- addVectoredContinueHandler := uintptr(0)
- if kernel32 != 0 {
- addVectoredContinueHandler = stdcall2(_GetProcAddress, kernel32, uintptr(unsafe.Pointer(&addVectoredContinueHandlerName[0])))
- }
- if addVectoredContinueHandler == 0 || unsafe.Sizeof(&kernel32) == 4 {
+ if _AddVectoredContinueHandler == nil || unsafe.Sizeof(&_AddVectoredContinueHandler) == 4 {
// use SetUnhandledExceptionFilter for windows-386 or
// if VectoredContinueHandler is unavailable.
// note: SetUnhandledExceptionFilter handler won't be called, if debugging.
stdcall1(_SetUnhandledExceptionFilter, funcPC(lastcontinuetramp))
} else {
- stdcall2(stdFunction(unsafe.Pointer(addVectoredContinueHandler)), 1, funcPC(firstcontinuetramp))
- stdcall2(stdFunction(unsafe.Pointer(addVectoredContinueHandler)), 0, funcPC(lastcontinuetramp))
+ stdcall2(_AddVectoredContinueHandler, 1, funcPC(firstcontinuetramp))
+ stdcall2(_AddVectoredContinueHandler, 0, funcPC(lastcontinuetramp))
}
stdcall2(_SetConsoleCtrlHandler, funcPC(ctrlhandler), 1)
@@ -158,10 +171,6 @@
// equivalent threads that all do a mix of GUI, IO, computations, etc.
// In such context dynamic priority boosting does nothing but harm, so we turn it off.
stdcall2(_SetProcessPriorityBoost, currentProcess, 1)
-
- if kernel32 != 0 {
- _GetQueuedCompletionStatusEx = stdFunction(unsafe.Pointer(stdcall2(_GetProcAddress, kernel32, uintptr(unsafe.Pointer(&getQueuedCompletionStatusExName[0])))))
- }
}
//go:nosplit
