I used classloader and Unsafe::definedAnonymous() to load generated bytecode byte[]. The usage of Class returned by classLoader.loadClass() succeeds while it fails with c.getMethod() in which c=Unsafe.defineAnonymousClass() API. So is the generated bytecode WRONG?
My code:
MainInliner loader = new MainInliner();
Class<?> c =null;
byte[] bytes = ...
if(args[0].equals("0")){
c = loader.loadClass(name, bytes, 0, bytes.length); // Classloader.loadClass.
}else{
c = Unsafe.defineAnonymousClass(Hoster, bytes, null);
}
Method m = c.getMethod("main", new Class<?>[] { String[].class });
The error is:
Exception Details:
Location:
code/sxu/asm/example/Caller.test(II)V @98: lload_3
Reason:
Type integer (current frame, locals[3]) is not assignable to long
Current Frame:
bci: @98
flags: { }
locals: { 'code/sxu/asm/example/Caller', integer, integer, integer, integer, integer, integer, integer, integer, integer }
stack: { 'java/io/PrintStream' }
Bytecode:
0000000: 1b85 2ab4 000e 1b1c 3e36 043a 0537 0619
0000010: 05b4 002a b600 3019 05b4 0033 b600 3060
0000020: 3608 1508 3609 1606 1509 a700 0385 6542
0000030: 1b2a b400 0e1c 033e 3604 3a05 3606 1905
0000040: b400 2ab6 0030 1905 b400 33b6 0030 6036
0000050: 0715 0736 0815 0615 08a7 0003 6036 05b2
0000060: 003d 21b6 0043 b1
Stackmap Table:
full_frame(@45,{Object[#2],Integer,Integer,Integer,Integer,Object[#21],Long,Integer,Integer},{Long,Integer})
full_frame(@92,{Object[#2],Integer,Integer,Integer,Integer,Object[#21],Integer,Integer,Integer,Integer},{Integer,Integer})
and the generated bytecode is:
public void test(int, int);
flags: ACC_PUBLIC
Code:
stack=5, locals=10, args_size=3
0: iload_1
1: i2l
2: aload_0
3: getfield #14 // Field _callee:Lcode/sxu/asm/example/Callee;
6: iload_1
7: iload_2
8: istore_3
9: istore 4
11: astore 5
13: lstore 6
15: aload 5
17: getfield #42 // Field code/sxu/asm/example/Callee._a:Ljava/lang/String;
20: invokevirtual #48 // Method java/lang/String.length:()I
23: aload 5
25: getfield #51 // Field code/sxu/asm/example/Callee._b:Ljava/lang/String;
28: invokevirtual #48 // Method java/lang/String.length:()I
31: iadd
32: istore 8
34: iload 8
36: istore 9
38: lload 6
40: iload 9
42: goto 45
45: i2l
46: lsub
47: lstore_3 //r..
48: iload_1
49: aload_0
50: getfield #14 // Field _callee:Lcode/sxu/asm/example/Callee;
53: iload_2
54: iconst_0
55: istore_3
56: istore 4
58: astore 5
60: istore 6 //The backup stack bottom variable.
62: aload 5
64: getfield #42 // Field code/sxu/asm/example/Callee._a:Ljava/lang/String;
67: invokevirtual #48 // Method java/lang/String.length:()I
70: aload 5
72: getfield #51 // Field code/sxu/asm/example/Callee._b:Ljava/lang/String;
75: invokevirtual #48 // Method java/lang/String.length:()I
78: iadd
79: istore 7
81: iload 7
83: istore 8
85: iload 6 //Push back 6
87: iload 8 //Repush 8
89: goto 92
//return calculate()
92: iadd
93: istore 5
95: getstatic #61 // Field java/lang/System.out:Ljava/io/PrintStream;
98: lload_3
99: invokevirtual #67 // Method java/io/PrintStream.println:(J)V
102: return
LocalVariableTable:
Start Length Slot Name Signature
15 30 5 this Lcode/sxu/asm/example/Callee;
15 30 4 t I
15 30 3 p I
34 11 8 tmp I
62 30 5 this Lcode/sxu/asm/example/Callee;
62 30 4 t I
62 30 3 p I
81 11 7 tmp I
0 103 0 this Lcode/sxu/asm/example/Caller;
0 103 1 a I
0 103 2 b I
48 55 3 r J
95 8 5 c I
LineNumberTable:
line 19: 0
line 16: 15
line 23: 34
line 21: 48
line 16: 62
line 23: 81
line 23: 95
line 30: 102
StackMapTable: number_of_entries = 2
frame_type = 255 /* full_frame */
offset_delta = 45
locals = [ class code/sxu/asm/example/Caller, int, int, int, int, class code/sxu/asm/example/Callee, long, int, int ]
stack = [ long, int ]
frame_type = 255 /* full_frame */
offset_delta = 46
locals = [ class code/sxu/asm/example/Caller, int, int, int, int, class code/sxu/asm/example/Callee, int, int, int, int ]
stack = [ int, int ]
}
This bytecode corresponding to inline a Callee method.
I checked this bytecode sequence, and it seems there is no error it. The variable 3 in the error message occurs 4 times, in which:
8: istore_3 //Popo up existing parameters for inlining.
47: lstore_3 //r. The local variable in the Caller method
55: istore_3 // Similiar to the label 8, pops stack paras to local variable.
98: lload_3 //Println parameter
The corresponding method is:
public class Caller{
public void test(int a, int b){
long r = (long)a- _callee.calculate(a, b);
int c = a +_callee.calculate(b, 0);
System.out.println(r);
}
}
public class Callee{
public int calculate(int t, int p){
int tmp=_a.length()+_b.length();
return tmp;
}}
loader.loadClass(bytes)mean? There is no suchClassLoader.loadClass(byte[])method. How did you generate the bytecode? Did you start with an existing method and modify it? – Antietamloader.loadClass(name, bytes, 0, bytes.length)mean? There is no suchClassLoader.loadClass(String, byte[], int, int)method. <- you didn't answer the first part of @bkail's ocmment. – Beltane55: istore_3– Leidintinto variable #3 @55, you can’t read alongfrom the same variable @98. It might be that the verification has been deferred when the class has been defined via an ordinary class loader. Besides that, I recommend not to use Reflection on classes created viaUnsafe.defineAnonymousClass, unless you want to play Russian roulette. UseMethodHandles to access the generated code… – RuphinaReflectionis a good suggestion for performance. – LeidMethodwill try to optimize itself by compiling an accessor class, but since anonymous classes can’t be accessed by other classes, you suddenly receiveErrors when callinginvoke. That might happen after twenty invocations or so. As said, that’s dependent on the implementation, hence, jre version. That’s why I said Russian roulette. – Ruphina