GetLastError() (with and without debugger)

[Manuel Bleichenbacher]

I've run a test with jdb, and the outcome is the same: the program behaves
incorrectly.

Do you guys know if this is caused by the debugger only, or if it is a
general problem that is more likely to occur with the debugger but could
also occur if run without debugger?

On Fri, Aug 12, 2022 at 3:16 PM Maurizio Cimadamore <
maurizio.cimadamore at oracle.com> wrote:

> Hi Manuel,
> thanks for submitting this issue.
>
> I think your hunch is probably correct - something inside the JDK is
> resetting the value of LastError.
>
> In Hotspot code I see some abstractions to preserve the LastError value
> (os_windows.cpp):
>
> // A number of wrappers for more frequently used system calls, to add standard logging.struct PreserveLastError {
>   const DWORD v;
>   PreserveLastError() : v(::GetLastError()) {}
>   ~PreserveLastError() { ::SetLastError(v); }
> };
>
>
> And this is used in a number of OS-specific function calls, to avoid
> polluting the last error value.
>
> That said, when you are running with a debugger, especially inside an IDE
> (which might add its own hooks), I think most bets are off, as the debugger
> might indeed perform additional native calls which might not preserve
> lastError correctly.
>
> One experiment would be to try and debugging using jdb - so that at least
> we'd rule the IDE out, and see if the issue is still there. If that's the
> case we'll try to reach out to somebody more intimate with architetcure of
> JPDA, to see if that's something that can be addressed (perhaps in a way
> similar to what hotspot code seems to be already doing).
>
> Thanks
> Maurizio
>
>
>
>
> On 12/08/2022 10:21, Manuel Bleichenbacher wrote:
>
> Thanks for the work on project Panama. It's an exciting technology. I'm
> using it to make native operating system services available to Java.
>
> On Windows I've run into an issue. This C/C++ Windows code:
>
>     BOOL res = WriteFile(INVALID_HANDLE_VALUE, NULL, 0, NULL, NULL);
>     DWORD err = GetLastError();
>     printf("WriteFile result: %d, GetLastError result: %d\n", res, err);
>
> prints (as expected):
>
>     WriteFile result: 0, GetLastError result: 6
>
> 6 is the value of the constant ERROR_INVALID_HANDLE.
>
> Using panama, I've translated the code to Java. The result is:
>
> Without debugger, the output is the same. Everything is ok.
>
> With the debugger, the result is incorrect:
>
>     WriteFile result: 0, GetLastError result: 0
>
> This is incorrect. WriteFile() indicates an error, but GetLastError()
> returns 0 (= NO_ERROR). Could it be that the debugger calls another Windows
> API function between those two functions, resetting the last error?
>
> In my project that's a major issue. Since the software behaves incorrectly
> with the debugger, the software can no longer be debugged. This doesn't
> just affect it when debugging this particular piece of code but anytime
> this code is run in a debugging session.
>
> Is there something I'm not doing incorrectly? Or is there a fix or
> workaround?
>
> Here's the Java code:
>
> import java.lang.foreign.*;import java.lang.invoke.MethodHandle;import static java.lang.foreign.MemoryAddress.NULL;import static java.lang.foreign.ValueLayout.ADDRESS;import static java.lang.foreign.ValueLayout.JAVA_INT;public class WinApi {
>     static final MethodHandle WriteFile$Func;    static final MethodHandle GetLastError$Func;    static final MemoryAddress INVALID_HANDLE_VALUE = MemoryAddress.ofLong(-1);    static {
>         var linker = Linker.nativeLinker();        var lookup = SymbolLookup.libraryLookup("Kernel32", MemorySession.global());        WriteFile$Func = linker.downcallHandle(
>                 lookup.lookup("WriteFile").get(),                FunctionDescriptor.of(JAVA_INT, ADDRESS, ADDRESS, JAVA_INT, ADDRESS, ADDRESS)
>         );        GetLastError$Func = linker.downcallHandle(
>                 lookup.lookup("GetLastError").get(),                FunctionDescriptor.of(JAVA_INT)
>         );    }
>
>     public static void main(String[] args) {
>         var res = WriteFile(INVALID_HANDLE_VALUE, NULL, 0, NULL, NULL);        var err = GetLastError();        System.out.printf("WriteFile result: %d, GetLastError result: %d\n", res, err);    }
>
>     static int WriteFile(MemoryAddress hFile, MemoryAddress lpBuffer, int nNumberOfBytesToWrite,                         MemoryAddress lpNumberOfBytesWritten, MemoryAddress lpOverlapped) {
>         try {
>             return (int) WriteFile$Func.invokeExact((Addressable)hFile, (Addressable)lpBuffer, nNumberOfBytesToWrite,                    (Addressable)lpNumberOfBytesWritten, (Addressable)lpOverlapped);        } catch (Throwable e) {
>             throw new RuntimeException(e);        }
>     }
>
>     static int GetLastError() {
>         try {
>             return (int) GetLastError$Func.invokeExact();        } catch (Throwable e) {
>             throw new RuntimeException(e);        }
>     }
> }
>
>
> Cheers
> Manuel
>
>
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