Mail Archives: cygwin/1998/08/10/17:09:42
> Henry J. Cobb wrote:
>
> In my continuing mission to use the CygWin32 tools to build Java
> products,
> I now have a makefile for Java Naive Interface DLLs, but unfortunately
> it only works with the M$ C compiler so far...
Henry,
Attached are some hints I've accumulated for doing JNI with GNU-WIN32.
--Andrew Mickish
http://www.andrew.cmu.edu/~mickish/
--------------------------------------------------------------------
Subject: More Java JNI with GNU-WIN32 gcc
Date: Mon, 10 Aug 1998 08:35:16 -0400
From: Andrew Mickish <mickish AT cmu DOT edu>
To: gnu-win32 AT cygnus DOT com
Here are a few more issues that came up when trying to compile
a JNI DLL with gcc.
* There are two different problems that could cause Unsatisfied
link errors. One is if the DLL is not found, and the other is
if the DLL is found but is unreadable or the specific function
cannot be found in it. These problems are distinguishable by
the stack trace that you get below the "Unsatisfied link error,"
and also by testing for changes in behavior when you run Java
after deliberately deleting the DLL or deliberately renaming
some arbitrary text file to be your DLL.
* The directory containing the DLL ought to be in your PATH.
The recommended way to set your path is to change it with the
System control panel and open a new window. The cygnus.bat file
munges the path a little itself, so my own path ends up looking
like this:
bash-2.01$ echo $PATH
/Cygnus/B19/H-i386-cygwin32/bin:/WINNT/system32:/WINNT:/utils:/enscript://E/jdk1.1.5/bin://E/java/HelloWorld
* I had to hand-edit the DEF file and put in an alias for the
exported function. Without the alias, it seems that Cygnus is
exporting the mangled name of the function with its offset
("...@8") and Java is looking for an unmangled name
(or vice versa). My DEF file looks like this:
bash-2.01$ cat hello.def
EXPORTS
Java_HelloWorld_displayHelloWorld=Java_HelloWorld_displayHelloWorld AT 8
dll_entry AT 12
Please let me know if any of this has been helpful.
--Andrew Mickish
mickish AT cmu DOT edu
-----------------------------------------------------------------
Subject: Java JNI with GNU-WIN32 gcc
Date: Thu, 11 Jun 1998 19:48:11 -0400
From: Andrew Mickish <mickish AT CMU DOT EDU>
To: gnu-win32 AT cygnus DOT com
With significant help from Bill Pringlemeir, I figured out how to compile
Sun's JNI tutorial HelloWorld example under GNU-WIN32 with gcc. I will keep
a
ZIP file of the gcc-compatible code at
http://www.andrew.cmu.edu/~am2q/HelloWorld.zip for future reference.
Please add this information to the GNU-WIN32 documentation and FAQ. As of
version 19.1, it is significantly more complicated to compile a
Java-compatible DLL under gcc than under Microsoft Visual C++. Even printf()
does not work in a gcc-compiled DLL, even thoough it works fine with VC++.
Will this be changing with future releases of GNU-WIN32?
Here are a few hints for how to compile a trivial JNI-compaible DLL with gcc:
1) You need init.cc, an element of building relocatable DLLs
2) There is a complicated linking procedure involving ld and intermediate
files:
ld --base-file hello.base --dll -o hello.dll HelloWorldImp.o init.o
$(LIB) -e _dll_entry AT 12
dlltool --as=as --dllname hello.dll --def hello.def --base-file
hello.base --output-exp hello.exp
ld --base-file hello.base hello.exp --dll -o hello.dll HelloWorldImp.o
init.o $(LIB) -e _dll_entry AT 12
dlltool --as=as --dllname hello.dll --def hello.def --base-file
hello.base --output-exp hello.exp
ld hello.exp --dll -o hello.dll HelloWorldImp.o init.o $(LIB) -e
_dll_entry AT 12
3) Printf will not work here. Use a Windows dialog box or call back into
Java to invoke
System.out.println():
void jprintf (JNIEnv *env, char* str) {
jstring jstr = (*env)->NewStringUTF(env, str);
jclass System_class = (*env)->FindClass(env, "java/lang/System");
jfieldID fid_out = (*env)->GetStaticFieldID(env, System_class, "out",
"Ljava/io/PrintStream;");
jobject out = (*env)->GetStaticObjectField(env, System_class, fid_out);
jclass PrintStream_class = (*env)->FindClass(env,
"java/io/PrintStream");
jmethodID mid_println = (*env)->GetMethodID(env, PrintStream_class,
"println", "(Ljava/lang/String;)V");
if (mid_println == 0) {
exit(1);
}
(*env)->CallVoidMethod(env, out, mid_println, jstr);
}
JNIEXPORT void JNICALL Java_HelloWorld_displayHelloWorld(JNIEnv *env,
jobject obj)
{
(void)env; (void)obj;
MessageBoxA(NULL,"Hello Jupiter!", "Hello world!", 0);
jprintf(env, "Hello Uranus!\n");
return;
}
A collection of files that implement Sun's JNI HelloWorld example may be
found
at http://www.andrew.cmu.edu/~am2q/HelloWorld.zip
--Andrew Mickish
mickish AT cmu DOT edu
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