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ART世界探险(10) - 异常处理

發(fā)布時間：2025/3/17 编程问答 19 豆豆

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ART世界探險(xiǎn)(10) - 異常處理

對于編譯Java的話，有一個問題不能不考慮，就是異常處理的問題。異常處理是基于Java的語句塊的，翻譯成本地代碼的話，需要針對這些指令的地址進(jìn)行一下重排。
我們來看下ART是如何實(shí)現(xiàn)異常處理的。

Java異常處理

首先復(fù)習(xí)一下Java。
Java有兩種Exception，一種是普通Exception，另一種是RuntimeException。非RuntimeException，如果沒有處理，就是沒有用try...catch塊包圍或者是throws聲明的話，會編譯不過。
而RuntimeException就沒有這個限制，不處理，就等運(yùn)行時crash再說吧。

Java源代碼

我們先寫兩個小函數(shù)試驗(yàn)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字節(jié)碼

從字節(jié)碼上我們可以看到，dealWithException中，0到4行是記錄在Exception table中的，如果出了Exception，則會跳轉(zhuǎn)到7開始的語句。
而withException方法，因?yàn)閽伋龅氖荝untimeException，也沒有try...catch，所以沒有Exception table.

public void withException();Code:0: new #11 // class java/lang/IllegalStateException3: dup4: invokespecial #12 // Method java/lang/IllegalStateException."<init>":()V7: athrowpublic void dealWtihException() throws java.io.IOException;Code:0: aload_01: invokevirtual #13 // Method withException:()V4: goto 237: astore_18: aload_19: instanceof #15 // class java/lang/RuntimeException12: ifeq 2315: new #16 // class java/io/IOException18: dup19: invokespecial #17 // Method java/io/IOException."<init>":()V22: athrow23: returnException table:from to target type0 4 7 Class java/lang/Exception

Dalvik指令和OAT指令

我們先看只拋個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@21050x0002: 7010 0642 0000 | invoke-direct {v0}, void java.lang.IllegalStateException.<init>() // method@169020x0005: 2700 | throw v0OatMethodOffsets (offset=0x002778f4)code_offset: 0x00663bdc gc_map: (offset=0x002848e8)OatQuickMethodHeader (offset=0x00663bc0)mapping_table: (offset=0x002deece)vmap_table: (offset=0x0030e0fa)v65535/r30QuickMethodFrameInfoframe_size_in_bytes: 32core_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: 0x0000GC 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)

前面還是保存現(xiàn)場，檢查有沒有被suspend.
然后調(diào)用pAllocObject去new一個IllegalStateException對象。
v0是sp+16

0x00663bf8: f94003e1 ldr x1, [sp]0x00663bfc: 52810720 mov w0, #0x8390x00663c00: f940d65e ldr lr, [tr, #424](pAllocObject)0x00663c04: d63f03c0 blr lrsuspend point dex PC: 0x0000GC 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: 0x0002GC map objects: v0 ([sp + #16]), v1 ([sp + #40])

只要是對象，就要調(diào)用構(gòu)造方法，下面就是計(jì)算和調(diào)用構(gòu)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, #0x10400x00663c28: f2a00050 movk x16, #0x2, lsl #160x00663c2c: f8706800 ldr x0, [x0, x16]0x00663c30: f940181e ldr lr, [x0, #48]0x00663c34: d63f03c0 blr lrsuspend point dex PC: 0x0002GC map objects: v0 ([sp + #16]), v1 ([sp + #40])

從v0(sp+16)把異常對象的引用讀回來，然后調(diào)用pDeliverException將其拋出去。

0x00663c38: b94013e0 ldr w0, [sp, #16]0x00663c3c: f942225e ldr lr, [tr, #1088](pDeliverException)0x00663c40: d63f03c0 blr lrsuspend point dex PC: 0x0005GC map objects: v0 ([sp + #16]), v1 ([sp + #40])0x00663c44: f9421e5e ldr lr, [tr, #1080](pTestSuspend)0x00663c48: d63f03c0 blr lrsuspend point dex PC: 0x0000GC 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@167840x0003: 0e00 | return-void0x0004: 0d00 | move-exception v00x0005: 2001 4908 | instance-of v1, v0, java.lang.RuntimeException // type@21210x0007: 3801 fcff | if-eqz v1, -40x0009: 2201 2008 | new-instance v1, java.io.IOException // type@20800x000b: 7010 ca41 0100 | invoke-direct {v1}, void java.io.IOException.<init>() // method@168420x000e: 2701 | throw v1OatMethodOffsets (offset=0x002778dc)code_offset: 0x0066341c gc_map: (offset=0x002ce33a)OatQuickMethodHeader (offset=0x00663400)mapping_table: (offset=0x00308696)vmap_table: (offset=0x0030e0fa)v65535/r30QuickMethodFrameInfoframe_size_in_bytes: 48core_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: 0x0000GC 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)

本地變量：
v0是sp+28
v1是sp+32

開始先將sp+56(v2)清0.
然后調(diào)用我們自己寫的withException方法。

0x00663438: b9403be0 ldr w0, [sp, #56]0x0066343c: b940001f ldr wzr, [x0]suspend point dex PC: 0x0000GC 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 lrsuspend point dex PC: 0x0000GC 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 retcatch entry dex PC: 0x0004

下面是處理Exception的部分：

Exception的類型放到w0中，然后去判斷類型是否已經(jīng)初始化過了。

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)

如果沒有初始化，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, #0x00x00663490: 340000a0 cbz w0, #+0x14 (addr 0x6634a4)

對象已經(jīng)初始化過了，就去調(diào)pInstanceofNonTrivial去做instanceof檢查。

0x00663494: b9400002 ldr w2, [x0]0x00663498: 6b01005f cmp w2, w10x0066349c: 54000441 b.ne #+0x88 (addr 0x663524)0x006634a0: 52800022 mov w2, #0x1

下面這段是判斷不是RuntimeException的子類，所以跳回，結(jié)束的情況。0x00663458是上面的返回部分的代碼。

0x006634a4: b90023e2 str w2, [sp, #32]0x006634a8: b94023e0 ldr w0, [sp, #32]0x006634ac: 7100001f cmp w0, #0x0 (0)0x006634b0: 1a9f17e1 cset w1, eq0x006634b4: 2a0103e0 mov w0, w10x006634b8: 35fffd00 cbnz w0, #-0x60 (addr 0x663458)

這里調(diào)用pAllocObject去new IOException的對象。

0x006634bc: f94003e1 ldr x1, [sp]0x006634c0: 52810400 mov w0, #0x8200x006634c4: f940d65e ldr lr, [tr, #424](pAllocObject)0x006634c8: d63f03c0 blr lrsuspend point dex PC: 0x0009GC 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: 0x000bGC map objects: v0 ([sp + #28]), v1 ([sp + #32]), v2 ([sp + #56])

下面當(dāng)然是調(diào)IOException的構(gòu)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, #0xe600x006634ec: f2a00050 movk x16, #0x2, lsl #160x006634f0: f8706800 ldr x0, [x0, x16]0x006634f4: f940181e ldr lr, [x0, #48]0x006634f8: d63f03c0 blr lrsuspend point dex PC: 0x000bGC map objects: v0 ([sp + #28]), v1 ([sp + #32]), v2 ([sp + #56])

最后調(diào)用pDeliveryException拋出去。

0x006634fc: b94023e0 ldr w0, [sp, #32]0x00663500: f942225e ldr lr, [tr, #1088](pDeliverException)0x00663504: d63f03c0 blr lrsuspend point dex PC: 0x000eGC map objects: v0 ([sp + #28]), v1 ([sp + #32]), v2 ([sp + #56])0x00663508: f9421e5e ldr lr, [tr, #1080](pTestSuspend)0x0066350c: d63f03c0 blr lrsuspend point dex PC: 0x0000GC map objects: v2 ([sp + #56])0x00663510: 17ffffca b #-0xd8 (addr 0x663438)

pInitializeType是檢查類型是否已經(jīng)初始化過了。

0x00663514: 52810920 mov w0, #0x8490x00663518: f9410a5e ldr lr, [tr, #528](pInitializeType)0x0066351c: d63f03c0 blr lrsuspend point dex PC: 0x0005GC map objects: v0 ([sp + #28]), v2 ([sp + #56])0x00663520: 17ffffd8 b #-0xa0 (addr 0x663480)

最后是instanceof的實(shí)現(xiàn)，pInstanceofNonTrivial

0x00663524: aa0103e0 mov x0, x10x00663528: aa0203e1 mov x1, x20x0066352c: f940fa5e ldr lr, [tr, #496](pInstanceofNonTrivial)0x00663530: d63f03c0 blr lrsuspend point dex PC: 0x0005GC map objects: v0 ([sp + #28]), v2 ([sp + #56])0x00663534: 2a0003e2 mov w2, w00x00663538: 17ffffdb b #-0x94 (addr 0x6634a4)

異常處理相關(guān)指令總結(jié)

Java字節(jié)碼Dalvik指令OAT過程

athrow

throw v0

pDeliverException

總結(jié)

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