windows: use MSVCRT.DLL instead of UCRT on i386

This allows the binaries to run on Windows XP, without needing any extra
DLLs. Tested in an x86 Windows XP SP3 virtual machine.

src/crypto/rand/rand_windows.go

@@ -1,6 +1,9 @@
 package rand
 
-import "errors"
+import (
+	"errors"
+	"unsafe"
+)
 
 func init() {
 	Reader = &reader{}
@@ -16,28 +19,22 @@ func (r *reader) Read(b []byte) (n int, err error) {
 		return
 	}
 
-	var randomByte uint32
-	for i := range b {
-		// Call rand_s every four bytes because it's a C int (always 32-bit in
-		// Windows).
-		if i%4 == 0 {
-			errCode := libc_rand_s(&randomByte)
-			if errCode != 0 {
-				// According to the documentation, it can return an error.
-				return n, errRandom
-			}
-		} else {
-			randomByte >>= 8
-		}
-		b[i] = byte(randomByte)
+	// Use the old RtlGenRandom, introduced in Windows XP.
+	// Even though the documentation says it is deprecated, it is widely used
+	// and probably won't go away anytime soon.
+	// See for example: https://github.com/golang/go/issues/33542
+	// For Windows 7 and newer, we might switch to ProcessPrng in the future
+	// (which is a documented function and might be a tiny bit faster).
+	ok := libc_RtlGenRandom(unsafe.Pointer(&b[0]), len(b))
+	if !ok {
+		return 0, errRandom
 	}
-
 	return len(b), nil
 }
 
-// Cryptographically secure random number generator.
-// https://docs.microsoft.com/en-us/cpp/c-runtime-library/reference/rand-s?view=msvc-170
-// errno_t rand_s(unsigned int* randomValue);
+// This function is part of advapi32.dll, and is called SystemFunction036 for
+// some reason. It's available on Windows XP and newer.
+// See: https://learn.microsoft.com/en-us/windows/win32/api/ntsecapi/nf-ntsecapi-rtlgenrandom
 //
-//export rand_s
-func libc_rand_s(randomValue *uint32) int32
+//export SystemFunction036
+func libc_RtlGenRandom(buf unsafe.Pointer, len int) bool

src/runtime/runtime_windows.go

@@ -42,10 +42,24 @@ func __p___argc() *int32
 //export __p___argv
 func __p___argv() **unsafe.Pointer
 
+type startupInfo struct {
+	newMode int32
+}
+
+//export __getmainargs
+func __getmainargs(argc *int32, argv, env **unsafe.Pointer, doWildcard int, startInfo *startupInfo) int32
+
+var performanceFrequency int64
+
 //export mainCRTStartup
 func mainCRTStartup() int {
 	preinit()
 
+	// Obtain the (constant) performance frequency when needed.
+	if GOARCH == "386" {
+		_QueryPerformanceFrequency(&performanceFrequency)
+	}
+
 	// Obtain the initial stack pointer right before calling the run() function.
 	// The run function has been moved to a separate (non-inlined) function so
 	// that the correct stack pointer is read.
@@ -78,9 +92,19 @@ var args []string
 func os_runtime_args() []string {
 	if args == nil {
 		// Obtain argc/argv from the environment.
-		_configure_narrow_argv(2)
-		argc := *__p___argc()
-		argv := *__p___argv()
+		var argc int32
+		var argv *unsafe.Pointer
+		if GOARCH == "386" {
+			// MSVCRT.DLL
+			var env *unsafe.Pointer
+			startInfo := startupInfo{newMode: 0}
+			__getmainargs(&argc, &argv, &env, 1, &startInfo)
+		} else {
+			// UCRT
+			_configure_narrow_argv(2)
+			argc = *__p___argc()
+			argv = *__p___argv()
+		}
 
 		// Make args slice big enough so that it can store all command line
 		// arguments.
@@ -146,10 +170,30 @@ func sleepTicks(d timeUnit) {
 	}
 }
 
+//export QueryPerformanceFrequency
+func _QueryPerformanceFrequency(*int64) bool
+
+//export QueryPerformanceCounter
+func _QueryPerformanceCounter(*int64) bool
+
 func ticks() timeUnit {
-	var unbiasedTime uint64
-	_QueryUnbiasedInterruptTime(&unbiasedTime)
-	return timeUnit(unbiasedTime)
+	if GOARCH == "386" {
+		// Unfortunately QueryUnbiasedInterruptTime is only available starting
+		// with Windows 7.
+
+		// Obtain counter (that runs at a fixed frequency).
+		var counter int64
+		_QueryPerformanceCounter(&counter)
+		// Convert this counter to ticks of 100ns (just like
+		// QueryUnbiasedInterruptTime).
+		// (We could also change the definition of ticks on GOOS=386 but that
+		// seems messy).
+		return timeUnit((counter * 10000000) / performanceFrequency)
+	} else {
+		var unbiasedTime uint64
+		_QueryUnbiasedInterruptTime(&unbiasedTime)
+		return timeUnit(unbiasedTime)
+	}
 }
 
 //go:linkname now time.now
@@ -237,17 +281,16 @@ func procUnpin() {
 }
 
 func hardwareRand() (n uint64, ok bool) {
-	var n1, n2 uint32
-	errCode1 := libc_rand_s(&n1)
-	errCode2 := libc_rand_s(&n2)
-	n = uint64(n1)<<32 | uint64(n2)
-	ok = errCode1 == 0 && errCode2 == 0
+	// Use the old RtlGenRandom, introduced in Windows XP.
+	// See the rationale in src/crypto/rand/rand_windows.go for why we use this
+	// one.
+	ok = _RtlGenRandom(unsafe.Pointer(&n), 8)
 	return
 }
 
-// Cryptographically secure random number generator.
-// https://docs.microsoft.com/en-us/cpp/c-runtime-library/reference/rand-s?view=msvc-170
-// errno_t rand_s(unsigned int* randomValue);
+// This function is part of advapi32.dll, and is called SystemFunction036 for
+// some reason. It's available on Windows XP and newer.
+// See: https://learn.microsoft.com/en-us/windows/win32/api/ntsecapi/nf-ntsecapi-rtlgenrandom
 //
-//export rand_s
-func libc_rand_s(randomValue *uint32) int32
+//export SystemFunction036
+func _RtlGenRandom(buf unsafe.Pointer, len int) bool