syscall: remove RtlGenRandom and move it into internal/syscall

There's on need to expose this to the frozen syscall package, and it
also doesn't need to be unsafe. So we move it into internal/syscall and
have the generator make a safer function signature.

Fixes #43704.

Change-Id: Iccae69dc273a0aa97ee6846eb537f1dc1412f2de
Reviewed-on: https://go-review.googlesource.com/c/go/+/283992
Run-TryBot: Jason A. Donenfeld <Jason@zx2c4.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>
Trust: Jason A. Donenfeld <Jason@zx2c4.com>

Author: zx2c4

api/go1.16.txt

@@ -430,10 +430,8 @@ pkg syscall (linux-arm-cgo), func AllThreadsSyscall(uintptr, uintptr, uintptr, u
 pkg syscall (linux-arm-cgo), func AllThreadsSyscall6(uintptr, uintptr, uintptr, uintptr, uintptr, uintptr, uintptr) (uintptr, uintptr, Errno)
 pkg syscall (linux-arm-cgo), func Setegid(int) error
 pkg syscall (linux-arm-cgo), func Seteuid(int) error
-pkg syscall (windows-386), func RtlGenRandom(*uint8, uint32) error
 pkg syscall (windows-386), method (*DLLError) Unwrap() error
 pkg syscall (windows-386), type SysProcAttr struct, NoInheritHandles bool
-pkg syscall (windows-amd64), func RtlGenRandom(*uint8, uint32) error
 pkg syscall (windows-amd64), method (*DLLError) Unwrap() error
 pkg syscall (windows-amd64), type SysProcAttr struct, NoInheritHandles bool
 pkg testing/fstest, func TestFS(fs.FS, ...string) error

src/crypto/rand/rand_windows.go

@@ -8,8 +8,8 @@
 package rand
 
 import (
+	"internal/syscall/windows"
 	"os"
-	"syscall"
 )
 
 func init() { Reader = &rngReader{} }
@@ -24,7 +24,7 @@ func (r *rngReader) Read(b []byte) (n int, err error) {
 		return 0, nil
 	}
 
-	err = syscall.RtlGenRandom(&b[0], inputLen)
+	err = windows.RtlGenRandom(b)
 	if err != nil {
 		return 0, os.NewSyscallError("RtlGenRandom", err)
 	}

src/internal/syscall/windows/syscall_windows.go

@@ -342,3 +342,5 @@ func LoadGetFinalPathNameByHandle() error {
 
 //sys	CreateEnvironmentBlock(block **uint16, token syscall.Token, inheritExisting bool) (err error) = userenv.CreateEnvironmentBlock
 //sys	DestroyEnvironmentBlock(block *uint16) (err error) = userenv.DestroyEnvironmentBlock
+
+//sys	RtlGenRandom(buf []byte) (err error) = advapi32.SystemFunction036

src/internal/syscall/windows/zsyscall_windows.go

@@ -234,7 +234,6 @@ func NewCallbackCDecl(fn interface{}) uintptr {
 //sys	CryptAcquireContext(provhandle *Handle, container *uint16, provider *uint16, provtype uint32, flags uint32) (err error) = advapi32.CryptAcquireContextW
 //sys	CryptReleaseContext(provhandle Handle, flags uint32) (err error) = advapi32.CryptReleaseContext
 //sys	CryptGenRandom(provhandle Handle, buflen uint32, buf *byte) (err error) = advapi32.CryptGenRandom
-//sys	RtlGenRandom(buf *uint8, bytes uint32) (err error) = advapi32.SystemFunction036
 //sys	GetEnvironmentStrings() (envs *uint16, err error) [failretval==nil] = kernel32.GetEnvironmentStringsW
 //sys	FreeEnvironmentStrings(envs *uint16) (err error) = kernel32.FreeEnvironmentStringsW
 //sys	GetEnvironmentVariable(name *uint16, buffer *uint16, size uint32) (n uint32, err error) = kernel32.GetEnvironmentVariableW