Booting a JVM
Posted by Mike Haller
on Tuesday, March 1. 2011
at 23:49
in Java
I'm right in the middle of implementing an interpreter for JVM bytecode. Today was the first time the system printed out the magic "Hello World!" message.The interpreted boot time for running on a JDK 1.6 host (i'm reusing their classes) is 4667ms. It takes 10ms to execute
System.out.printlnt("Hello World!");.Starting up the Virtual Machine and executing any class is pretty easy:
final VirtualMachine vm = new VirtualMachine();
final Classpath classpath = new Classpath();
classpath.addLoader(new HostVMResourceLoader()); // Re-uses JDK classes
classpath.addFolder("C:/Example/bin"); // The HelloWorld project
vm.setClasspath(classpath);
vm.start();
vm.execute("org/example/HelloWorld");
The output can be seen in the screenshot:
The following is an histogram of the bytecodes being executed, only to start up and initialize the JVM.
That includes booting up the System class, character sets, ThreadGroups, Reflection, NIO, and a lot of native methods which had to be replaced.
[01] aconst_null 3398 invocations [02] iconst_m1 31 invocations [03] iconst_0 33689 invocations [04] iconst_1 11795 invocations [05] iconst_2 445 invocations [06] iconst_3 181 invocations [07] iconst_4 121 invocations [08] iconst_5 57 invocations [09] lconst_0 18 invocations [0a] lconst_1 3 invocations [0b] fconst_0 19 invocations [10] bipush 58215 invocations [11] sipush 222 invocations [12] ldc 1287 invocations [13] ldc_w 494 invocations [14] ldc2_w 15 invocations [15] iload 362633 invocations [16] lload 5 invocations [19] aload 81878 invocations [1a] iload_0 100335 invocations [1b] iload_1 236106 invocations [1c] iload_2 1208 invocations [1d] iload_3 1383 invocations [1e] lload_0 3 invocations [1f] lload_1 4 invocations [20] lload_2 6 invocations [22] fload_0 15 invocations [24] fload_2 52 invocations [25] fload_3 24 invocations [26] dload_0 1 invocations [2a] aload_0 306476 invocations [2b] aload_1 43405 invocations [2c] aload_2 25744 invocations [2d] aload_3 83195 invocations [32] aaload 794 invocations [33] baload 6 invocations [34] caload 78421 invocations [36] istore 161005 invocations [37] lstore 2 invocations [3a] astore 26685 invocations [3b] istore_0 2 invocations [3c] istore_1 907 invocations [3d] istore_2 121 invocations [3e] istore_3 185 invocations [3f] lstore_0 1 invocations [40] lstore_1 2 invocations [41] lstore_2 3 invocations [4b] astore_0 35 invocations [4c] astore_1 742 invocations [4d] astore_2 2411 invocations [4e] astore_3 19006 invocations [4f] iastore 20 invocations [53] aastore 1654 invocations [54] bastore 19 invocations [55] castore 265 invocations [57] pop 808 invocations [58] pop2 4 invocations [59] dup 4418 invocations [5a] dup_x1 4 invocations [5c] dup2 1 invocations [60] iadd 86425 invocations [61] ladd 1 invocations [64] isub 61816 invocations [68] imul 814 invocations [6a] fmul 11 invocations [70] irem 135 invocations [78] ishl 8 invocations [7a] ishr 9 invocations [7c] iushr 8 invocations [7e] iand 163 invocations [7f] land 1 invocations [80] ior 25086 invocations [81] lor 1 invocations [82] ixor 8 invocations [84] iinc 29597 invocations [85] i2l 1 invocations [86] i2f 17 invocations [8b] f2i 11 invocations [91] i2b 13 invocations [92] i2c 25083 invocations [94] lcmp 13 invocations [95] fcmpl 19 invocations [96] fcmpg 19 invocations [99] ifeq 25358 invocations [9a] ifne 42109 invocations [9b] iflt 102593 invocations [9c] ifge 12405 invocations [9d] ifgt 27 invocations [9e] ifle 6280 invocations [9f] if_icmpeq 51280 invocations [a0] if_icmpne 813 invocations [a1] if_icmplt 77656 invocations [a2] if_icmpge 52068 invocations [a3] if_icmpgt 73 invocations [a4] if_icmple 52 invocations [a5] if_acmpeq 1612 invocations [a6] if_acmpne 2072 invocations [a7] goto 66816 invocations [a8] jsr 1 invocations [a9] ret 1 invocations [ab] lookupswitch 1 invocations [ac] ireturn 164404 invocations [ad] lreturn 6 invocations [b0] areturn 14314 invocations [b1] return 6938 invocations [b2] getstatic 39043 invocations [b3] putstatic 201 invocations [b4] getfield 310885 invocations [b5] putfield 15212 invocations [b6] invokevirtual 102940 invocations [b7] invokespecial 3603 invocations [b8] invokestatic 65929 invocations [b9] invokeinterface 13227 invocations [bb] new 950 invocations [bc] newarray 40 invocations [bd] anewarray 477 invocations [be] arraylength 764 invocations [c0] checkcast 23360 invocations [c1] instanceof 55 invocations [c2] monitorenter 151 invocations [c3] monitorexit 151 invocations [c6] ifnull 15595 invocations [c7] ifnonnull 19950 invocations Total: 3118655
Three million bytecode instructions executed to get a little message on the screen.
