/zxp-native-usb-adapter-64bit-hack

Primary LanguageCMIT LicenseMIT

Patch for ZebraNativeUsbAdapter_64.dll (memory allocator workaround)

Zebra Link-OS Multiplatform SDK for Desktop Java - Card (Build: 2.12.3782) comes with the ZebraNativeUsbAdapter_64.dll, although there is an implementation bug that would cause the SDK to crash with the following error when running under 64 bit Java.

Crash

#
# A fatal error has been detected by the Java Runtime Environment:
#
#  EXCEPTION_ACCESS_VIOLATION (0xc0000005) at pc=0x00007ffedbdb25be, pid=11668, tid=0x0000000000002504
#
# JRE version: Java(TM) SE Runtime Environment (8.0_381) (build 1.8.0_381-b09)
# Java VM: Java HotSpot(TM) 64-Bit Server VM (25.381-b09 mixed mode windows-amd64 compressed oops)
# Problematic frame:
# C  [ZebraNativeUsbAdapter_64.dll+0x25be]
#
# Failed to write core dump. Minidumps are not enabled by default on client versions of Windows
#
# If you would like to submit a bug report, please visit:
#   http://bugreport.java.com/bugreport/crash.jsp
# The crash happened outside the Java Virtual Machine in native code.
# See problematic frame for where to report the bug.
#

Patch

  1. Download release: Patch_ZebraNativeUsbAdapter_64_20231119R03.zip
  2. Replace your original ZebraNativeUsbAdapter_64.dll with the two DLL files that are contained in the archive.

Technical details

Whenever Java SDK asks to open the connection with the printer, the original DLL would allocate a heap object representing the printer connection and return a pointer back to Java SDK. However, there is an implementation bug that would cause the DLL to cast the pointer to uint32_t before returning it. Similarly, the exported functions that allow subsequent printer interaction would also shrink the pointer right in their prologue.

The patch features a special proxy DLL called MQALLOC.dll that re-implements the C++ dynamic allocator (operator new and operator delete). The additional DLL will ensure that heap objects are always allocated on low virtual addresses (pointer values significantly below 2^32). Thus, the pointer values will not get damaged, even if they would be inappropriately casted to uint32_t anywhere.

Known limitations

  • The hack would cause a crash if there are more than 468 open printer handles at once (this shouldn't ever happen in practice, unless there is a bug somewhere else).

Debugging

Set DEBUG_MQALLOC=1 environment variable and launch Java with your application. Debug printouts from the allocator will be written on standard error stream.

Disclaimer

Information and binary releases are provided here only to increase the compatibility.