@vaaneeunbnd reported an issue at gitter:

I am using GLKMatrix4 as a modelviewmatrix in my robovm app but whenever I try to apply translation to it: modelViewMatrix.createTranslation(0.0f, 0.0f, -1.0f); It crashes without a debug log, can someone please help me with this

But diagnostic report contains a crash log:

Exception Type:        EXC_BAD_ACCESS (SIGBUS)
Exception Codes:       KERN_PROTECTION_FAILURE at 0x0000000106a416e0
Exception Note:        EXC_CORPSE_NOTIFY
VM Regions Near 0x106a416e0:
--> __TEXT                      106a18000-106a48000 
0   Java_libcore_io_Memory_pokeInt + 11
1   [J]libcore.io.Memory.pokeInt(JIZ)V + 119
2   [j]libcore.io.Memory.pokeInt(JIZ)V[clinit] + 71
3   [j]libcore.io.Memory.pokeInt(JIZ)V[Invokestatic(java/nio/MemoryBlock)] + 14
4   [J]java.nio.MemoryBlock.pokeInt(IILjava/nio/ByteOrder;)V + 184 (MemoryBlock.java:220)
5   [j]java.nio.MemoryBlock.pokeInt(IILjava/nio/ByteOrder;)V[Invokevirtual(java/nio/Dire
6   [J]java.nio.DirectByteBuffer.putFloat(IF)Ljava/nio/ByteBuffer; + 393 (DirectByteBuffer.java
7   [j]java.nio.ByteBuffer.putFloat(IF)Ljava/nio/ByteBuffer;[Invokevirtual(java/nio/Byte
8   [J]java.nio.ByteBufferAsFloatBuffer.put(IF)Ljava/nio/FloatBuffer; + 208 (Byt
9   [j]java.nio.FloatBuffer.put(IF)Ljava/nio/FloatBuffer;[Invokevirtual(org/robovm/apple/glki
10  [J]org.robovm.apple.glkit.GLKMatrix4.createTranslation(FFF)Lorg/robovm/apple/glkit/GLKM
11  [j]org.robovm.apple.glkit.GLKMatrix4.createTranslation(FFF)Lorg/robovm/apple/glkit/GLKM
12  [j]org.robovm.apple.glkit.GLKMatrix4.createTranslation(FFF)Lorg/robovm/apple/glkit/GLKMatrix4;[Invokestatic(com/mycompany/myapp/MyViewController)] + 9

And code that triggered it looks like the bellow:

public static GLKMatrix4 createTranslation(float tx, float ty, float tz) {
    GLKMatrix4 m = Identity();
    FloatBuffer m_m = m.getM();
    m_m.put(12, tx);
    m_m.put(13, ty);
    m_m.put(14, tz);
    return m;
}

m_m.put(12, tx) causes KERN_PROTECTION_FAILURE due writing to prohibited memory region. GLKMatrix4 was returned by Identity() seems valid but can’t be modified. It obtains value from following global variable:

@GlobalValue(symbol="GLKMatrix4Identity", optional=true)
public static native @ByVal GLKMatrix4 Identity();    

Quick check shows that its is located not in __DATA segment and linker might put it to __TEXT where any modifications are not possible:

nm GLKit | grep GLKMatrix4Identity
00000000000296b0 S _GLKMatrix4Identity

But Identity() is defined with @ByVal annotation that means it should return it by-value, e.g. make a copy of data on the heap.

Root case – @ByVal doesn’t affect getters for GlobalValues/Structs

Existing implementation just marshal the pointer from GlobalValue/Struct member that corresponds to the @ByRef behaviour. Here is an example that demonstrates the bug:

CGRect rect = new CGRect(1, 2, 3, 4);
CGPoint origin = rect.getOrigin();
System.out.println("x=" + origin.getX() +", y=" + origin.getY());
rect.setOrigin(new CGPoint(5, 6));
System.out.println("x=" + origin.getX() +", y=" + origin.getY());

prints:

x=1.0, y=2.0
x=5.0, y=6.0

The fix is to make a copy of structure onto the heap and then marshal the pointer. Fix is delivered as PR550.

Side effect of the fix

The fix breaks existing code that is built around this bug. An example is CGRect constructor that stops working:

public CGRect(double x, double y, double width, double height) {
    getOrigin().setX(x).setY(y);
    getSize().setWidth(width).setHeight(height);
}

After the fix getOrigin()/getSize() return a copy (byValue) structures. And changes to them doesn’t affect CGRect struct itself anymore.