ART世界探险(10) - 异常处理
对于编译Java的话，有一个问题不能不考虑，就是异常处理的问题。异常处理是基于Java的语句块的，翻译成本地代码的话，需要针对这些指令的地址进行一下重排。
我们来看下ART是如何实现异常处理的。
Java异常处理
首先复习一下Java。
Java有两种Exception，一种是普通Exception，另一种是RuntimeException。非RuntimeException，如果没有处理，就是没有用try...catch块包围或者是throws声明的话，会编译不过。
而RuntimeException就没有这个限制，不处理，就等运行时crash再说吧。
Java源代码
我们先写两个小函数试验一下：
public void withException(){
throw new IllegalStateException();
}
public void dealWtihException() throws IOException{
try{
withException();
}catch(Exception e){
if(e instanceof RuntimeException) throw new IOException();
}
}
Class字节码
从字节码上我们可以看到，dealWithException中，0到4行是记录在Exception table中的，如果出了Exception，则会跳转到7开始的语句。
而withException方法，因为抛出的是RuntimeException，也没有try...catch，所以没有Exception table.
public void withException();
Code:
0: new #11 // class java/lang/IllegalStateException
3: dup
4: invokespecial #12 // Method java/lang/IllegalStateException."<init>":()V
7: athrow
public void dealWtihException() throws java.io.IOException;
Code:
0: aload_0
1: invokevirtual #13 // Method withException:()V
4: goto 23
7: astore_1
8: aload_1
9: instanceof #15 // class java/lang/RuntimeException
12: ifeq 23
15: new #16 // class java/io/IOException
18: dup
19: invokespecial #17 // Method java/io/IOException."<init>":()V
22: athrow
23: return
Exception table:
from to target type
0 4 7 Class java/lang/Exception
Dalvik指令和OAT指令
我们先看只抛个Exception的withException
7: void com.yunos.xulun.testcppjni2.SampleClass.withException() (dex_method_idx=16784)
DEX CODE:
0x0000: 2200 3908 | new-instance v0, java.lang.IllegalStateException // type@2105
0x0002: 7010 0642 0000 | invoke-direct {v0}, void java.lang.IllegalStateException.<init>() // method@16902
0x0005: 2700 | throw v0
OatMethodOffsets (offset=0x002778f4)
code_offset: 0x00663bdc
gc_map: (offset=0x002848e8)
OatQuickMethodHeader (offset=0x00663bc0)
mapping_table: (offset=0x002deece)
vmap_table: (offset=0x0030e0fa)
v65535/r30
QuickMethodFrameInfo
frame_size_in_bytes: 32
core_spill_mask: 0x40000000 (r30)
fp_spill_mask: 0x00000000
vr_stack_locations:
locals: v0[sp + #16]
ins: v1[sp + #40]
method*: v2[sp + #0]
outs: v0[sp + #8]
CODE: (code_offset=0x00663bdc size_offset=0x00663bd8 size=116)...
0x00663bdc: d1400bf0 sub x16, sp, #0x2000 (8192)
0x00663be0: b940021f ldr wzr, [x16]
suspend point dex PC: 0x0000
GC map objects: v1 ([sp + #40])
0x00663be4: f81e0fe0 str x0, [sp, #-32]!
0x00663be8: f9000ffe str lr, [sp, #24]
0x00663bec: b9002be1 str w1, [sp, #40]
0x00663bf0: 79400250 ldrh w16, [tr] (state_and_flags)
0x00663bf4: 35000290 cbnz w16, #+0x50 (addr 0x663c44)
前面还是保存现场，检查有没有被suspend.
然后调用pAllocObject去new一个IllegalStateException对象。
v0是sp+16
0x00663bf8: f94003e1 ldr x1, [sp]
0x00663bfc: 52810720 mov w0, #0x839
0x00663c00: f940d65e ldr lr, [tr, #424] (pAllocObject)
0x00663c04: d63f03c0 blr lr
suspend point dex PC: 0x0000
GC map objects: v1 ([sp + #40])
0x00663c08: b90013e0 str w0, [sp, #16]
0x00663c0c: b94013e0 ldr w0, [sp, #16]
0x00663c10: b940001f ldr wzr, [x0]
suspend point dex PC: 0x0002
GC map objects: v0 ([sp + #16]), v1 ([sp + #40])
只要是对象，就要调用构造方法，下面就是计算和调用构造方法。
0x00663c14: b9000fe0 str w0, [sp, #12]
0x00663c18: b9400fe1 ldr w1, [sp, #12]
0x00663c1c: f94003e0 ldr x0, [sp]
0x00663c20: b9400400 ldr w0, [x0, #4]
0x00663c24: d2820810 mov x16, #0x1040
0x00663c28: f2a00050 movk x16, #0x2, lsl #16
0x00663c2c: f8706800 ldr x0, [x0, x16]
0x00663c30: f940181e ldr lr, [x0, #48]
0x00663c34: d63f03c0 blr lr
suspend point dex PC: 0x0002
GC map objects: v0 ([sp + #16]), v1 ([sp + #40])
从v0(sp+16)把异常对象的引用读回来，然后调用pDeliverException将其抛出去。
0x00663c38: b94013e0 ldr w0, [sp, #16]
0x00663c3c: f942225e ldr lr, [tr, #1088] (pDeliverException)
0x00663c40: d63f03c0 blr lr
suspend point dex PC: 0x0005
GC map objects: v0 ([sp + #16]), v1 ([sp + #40])
0x00663c44: f9421e5e ldr lr, [tr, #1080] (pTestSuspend)
0x00663c48: d63f03c0 blr lr
suspend point dex PC: 0x0000
GC map objects: v1 ([sp + #40])
0x00663c4c: 17ffffeb b #-0x54 (addr 0x663bf8)
下面再看dealWtihException的：
1: void com.yunos.xulun.testcppjni2.SampleClass.dealWtihException() (dex_method_idx=16778)
DEX CODE:
0x0000: 6e10 9041 0200 | invoke-virtual {v2}, void com.yunos.xulun.testcppjni2.SampleClass.withException() // method@16784
0x0003: 0e00 | return-void
0x0004: 0d00 | move-exception v0
0x0005: 2001 4908 | instance-of v1, v0, java.lang.RuntimeException // type@2121
0x0007: 3801 fcff | if-eqz v1, -4
0x0009: 2201 2008 | new-instance v1, java.io.IOException // type@2080
0x000b: 7010 ca41 0100 | invoke-direct {v1}, void java.io.IOException.<init>() // method@16842
0x000e: 2701 | throw v1
OatMethodOffsets (offset=0x002778dc)
code_offset: 0x0066341c
gc_map: (offset=0x002ce33a)
OatQuickMethodHeader (offset=0x00663400)
mapping_table: (offset=0x00308696)
vmap_table: (offset=0x0030e0fa)
v65535/r30
QuickMethodFrameInfo
frame_size_in_bytes: 48
core_spill_mask: 0x40000000 (r30)
fp_spill_mask: 0x00000000
vr_stack_locations:
locals: v0[sp + #28] v1[sp + #32]
ins: v2[sp + #56]
method*: v3[sp + #0]
outs: v0[sp + #8]
CODE: (code_offset=0x0066341c size_offset=0x00663418 size=288)...
0x0066341c: d1400bf0 sub x16, sp, #0x2000 (8192)
0x00663420: b940021f ldr wzr, [x16]
suspend point dex PC: 0x0000
GC map objects: v2 ([sp + #56])
0x00663424: f81d0fe0 str x0, [sp, #-48]!
0x00663428: f90017fe str lr, [sp, #40]
0x0066342c: b9003be1 str w1, [sp, #56]
0x00663430: 79400250 ldrh w16, [tr] (state_and_flags)
0x00663434: 350006b0 cbnz w16, #+0xd4 (addr 0x663508)
本地变量：
v0是sp+28
v1是sp+32
开始先将sp+56(v2)清0.
然后调用我们自己写的withException方法。
0x00663438: b9403be0 ldr w0, [sp, #56]
0x0066343c: b940001f ldr wzr, [x0]
suspend point dex PC: 0x0000
GC map objects: v2 ([sp + #56])
0x00663440: b9001be0 str w0, [sp, #24]
0x00663444: b9401be1 ldr w1, [sp, #24]
0x00663448: b9400020 ldr w0, [x1]
0x0066344c: f9418c00 ldr x0, [x0, #792]
0x00663450: f940181e ldr lr, [x0, #48]
0x00663454: d63f03c0 blr lr
suspend point dex PC: 0x0000
GC map objects: v2 ([sp + #56])
返回值也用不到，所以直接返回了。
0x00663458: f94017fe ldr lr, [sp, #40]
0x0066345c: 9100c3ff add sp, sp, #0x30 (48)
0x00663460: d65f03c0 ret
catch entry dex PC: 0x0004
下面是处理Exception的部分：
Exception的类型放到w0中，然后去判断类型是否已经初始化过了。
0x00663464: b9408a40 ldr w0, [tr, #136] (exception)
0x00663468: b9008a5f str wzr, [tr, #136] (exception)
0x0066346c: b9001fe0 str w0, [sp, #28]
0x00663470: f94003e0 ldr x0, [sp]
0x00663474: b9400800 ldr w0, [x0, #8]
0x00663478: b9613000 ldr w0, [x0, #8496]
0x0066347c: 340004c0 cbz w0, #+0x98 (addr 0x663514)
如果没有初始化，那就真接跳0x663490，返回
0x00663480: b9001be0 str w0, [sp, #24]
0x00663484: b9401fe0 ldr w0, [sp, #28]
0x00663488: b9401be1 ldr w1, [sp, #24]
0x0066348c: 52800002 mov w2, #0x0
0x00663490: 340000a0 cbz w0, #+0x14 (addr 0x6634a4)
对象已经初始化过了，就去调pInstanceofNonTrivial去做instanceof检查。
0x00663494: b9400002 ldr w2, [x0]
0x00663498: 6b01005f cmp w2, w1
0x0066349c: 54000441 b.ne #+0x88 (addr 0x663524)
0x006634a0: 52800022 mov w2, #0x1
下面这段是判断不是RuntimeException的子类，所以跳回，结束的情况。0x00663458是上面的返回部分的代码。
0x006634a4: b90023e2 str w2, [sp, #32]
0x006634a8: b94023e0 ldr w0, [sp, #32]
0x006634ac: 7100001f cmp w0, #0x0 (0)
0x006634b0: 1a9f17e1 cset w1, eq
0x006634b4: 2a0103e0 mov w0, w1
0x006634b8: 35fffd00 cbnz w0, #-0x60 (addr 0x663458)
这里调用pAllocObject去new IOException的对象。
0x006634bc: f94003e1 ldr x1, [sp]
0x006634c0: 52810400 mov w0, #0x820
0x006634c4: f940d65e ldr lr, [tr, #424] (pAllocObject)
0x006634c8: d63f03c0 blr lr
suspend point dex PC: 0x0009
GC map objects: v0 ([sp + #28]), v2 ([sp + #56])
0x006634cc: b90023e0 str w0, [sp, #32]
0x006634d0: b94023e0 ldr w0, [sp, #32]
0x006634d4: b940001f ldr wzr, [x0]
suspend point dex PC: 0x000b
GC map objects: v0 ([sp + #28]), v1 ([sp + #32]), v2 ([sp + #56])
下面当然是调IOException的构造方法了：
0x006634d8: b9001be0 str w0, [sp, #24]
0x006634dc: b9401be1 ldr w1, [sp, #24]
0x006634e0: f94003e0 ldr x0, [sp]
0x006634e4: b9400400 ldr w0, [x0, #4]
0x006634e8: d281cc10 mov x16, #0xe60
0x006634ec: f2a00050 movk x16, #0x2, lsl #16
0x006634f0: f8706800 ldr x0, [x0, x16]
0x006634f4: f940181e ldr lr, [x0, #48]
0x006634f8: d63f03c0 blr lr
suspend point dex PC: 0x000b
GC map objects: v0 ([sp + #28]), v1 ([sp + #32]), v2 ([sp + #56])
最后调用pDeliveryException抛出去。
0x006634fc: b94023e0 ldr w0, [sp, #32]
0x00663500: f942225e ldr lr, [tr, #1088] (pDeliverException)
0x00663504: d63f03c0 blr lr
suspend point dex PC: 0x000e
GC map objects: v0 ([sp + #28]), v1 ([sp + #32]), v2 ([sp + #56])
0x00663508: f9421e5e ldr lr, [tr, #1080] (pTestSuspend)
0x0066350c: d63f03c0 blr lr
suspend point dex PC: 0x0000
GC map objects: v2 ([sp + #56])
0x00663510: 17ffffca b #-0xd8 (addr 0x663438)
pInitializeType是检查类型是否已经初始化过了。
0x00663514: 52810920 mov w0, #0x849
0x00663518: f9410a5e ldr lr, [tr, #528] (pInitializeType)
0x0066351c: d63f03c0 blr lr
suspend point dex PC: 0x0005
GC map objects: v0 ([sp + #28]), v2 ([sp + #56])
0x00663520: 17ffffd8 b #-0xa0 (addr 0x663480)
最后是instanceof的实现，pInstanceofNonTrivial
0x00663524: aa0103e0 mov x0, x1
0x00663528: aa0203e1 mov x1, x2
0x0066352c: f940fa5e ldr lr, [tr, #496] (pInstanceofNonTrivial)
0x00663530: d63f03c0 blr lr
suspend point dex PC: 0x0005
GC map objects: v0 ([sp + #28]), v2 ([sp + #56])
0x00663534: 2a0003e2 mov w2, w0
0x00663538: 17ffffdb b #-0x94 (addr 0x6634a4)
异常处理相关指令总结
| Java字节码 | Dalvik指令 | OAT过程 |
|---|---|---|
| athrow | throw v0 | pDeliverException |
