Re: Classpath build process and VM-specific issues

[Etienne Gagnon]

Andrew Haley wrote:
> malloc() returns a char*, not a jbyte*.

So, can you tell me the difference between a jbyte and a "signed char"?

> Sigh.  No it isn't, and this code will break with gcc.

OK, maybe I am tired and I don't see it.  GCC -Wall does not complain
about the attached example.

> ...  Also, "when a pointer to an object is converted
> to a pointer to a character type, the result points to the lowest
> addressed byte of the object.  Successive increments of the result, up
> to the size of the object, yield pointers to the remaining bytes of
> the object."


We agree on this.  Now: what's different between "signed char" and "jbyte"?
Can they actually be distinct on some platform?

Etienne

--
Etienne M. Gagnon, Ph.D.             http://www.info.uqam.ca/~egagnon/
SableVM:                                       http://www.sablevm.org/
SableCC:                                       http://www.sablecc.org/

/* DO NOT EDIT THIS FILE - it is machine generated */
#include <jni.h>
/* Header for class JNITest */

#ifndef _Included_JNITest
#define _Included_JNITest
#ifdef __cplusplus
extern "C"
{
#endif
/*
 * Class:     JNITest
 * Method:    getPtr
 * Signature: ()[B
 */
  JNIEXPORT jbyteArray JNICALL Java_JNITest_getPtr (JNIEnv *, jclass);

/*
 * Class:     JNITest
 * Method:    testPtr
 * Signature: ([B)V
 */
  JNIEXPORT void JNICALL Java_JNITest_testPtr (JNIEnv *, jclass, jbyteArray);

#ifdef __cplusplus
}
#endif
#endif

public class JNITest
{
    static
    {
        System.loadLibrary("test");
    }

    public static void main(String[] args)
    {
        byte[] nativePtr = getPtr();
        testPtr(nativePtr);
    }

    private static native byte[] getPtr();
    private static native void testPtr(byte[] nativPtr);
}

#include <jni.h>
#include <stdio.h>
#include <stdlib.h>

/*
 * Class:     JNITest
 * Method:    getPtr
 * Signature: ()[B
 */
JNIEXPORT jbyteArray JNICALL
Java_JNITest_getPtr (JNIEnv * env, jclass class)
{
  int *int_ptr = (int *) malloc (sizeof (int));;
  *int_ptr = 0x47;
 
  jbyteArray nativePtr = (*env)->NewByteArray (env, (jint) sizeof (int *));

  if (nativePtr == NULL)
    return NULL;

  (*env)->SetByteArrayRegion (env, nativePtr, 0, (int) sizeof (int *),
                              (char *) &int_ptr);

  return nativePtr;
}

/*
 * Class:     JNITest
 * Method:    testPtr
 * Signature: ([B)V
 */
JNIEXPORT void JNICALL
Java_JNITest_testPtr (JNIEnv * env, jclass class, jbyteArray nativePtr)
{
  int *int_ptr;
  (*env)->GetByteArrayRegion (env, nativePtr, 0, (jint) sizeof (int *),
                              (jbyte *) & int_ptr);
  printf ("value = %x\n", *int_ptr);
}