GetLastError() (with and without debugger)

[Radosław Smogura]

Hi all,

I could guess that debugger uses network and uses low level API to send and receive packets, which can cause error to be reset. But this is only my guess.

Kind regards,
Rado Smogura

From: Maurizio Cimadamore<mailto:maurizio.cimadamore at oracle.com>
Sent: Friday, August 12, 2022 4:51 PM
To: Pedro Lamarão<mailto:pedro.lamarao at prodist.com.br>; Manuel Bleichenbacher<mailto:manuel.bleichenbacher at gmail.com>
Cc: panama-dev at openjdk.org<mailto:panama-dev at openjdk.org>
Subject: Re: GetLastError() (with and without debugger)



On 12/08/2022 15:43, Pedro Lamarão wrote:

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.


This would be a blocker for all applications of Windows API functions via panama.
Windows Sockets has a similar mechanism called WSAGetLastError.

And JNI - I doubt there's anything Panama specific here (unless proven otherwise).

So that it's clear - it's not that GetLastError fails in general. It fails when a debugger is attached. As I explained, this could be due to _which_ debugger is attached, or some existing issue (predating Panama) in the way jdb/JPDA deal with some Windows system calls.

Maurizio

As far as I know, GetLastError and WSAGetLastError are getter-like functions for effectively thread local data.
It is safe to call Windows API functions from inside the same process but another thread.
If some piece of software infrastructure has perturbed your program, then it has called a Windows API function from inside our program


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



--
Pedro Lamarão
https://www.prodist.com.br
Securing Critical Systems
Tel: +55 11 4380-6585
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