Android：ART虚拟机运行速度之OAT

ART虚拟机使用的是oat文件，oat文件其实已经是一种可执行文件了，就跟system/bin下面的文件是同一个类型。可执行文件里面就是一些机器码，所以ART虚拟机就运行得很快啦。

1.OAT文件是ELF可执行文件

下面我们来看看优酷apk的oat文件罗。咦？？oat文件怎么是已odex结尾呢？？其实就是为了兼容之前的dalvick虚拟机啦。

youku

通过file命令可以看到他是elf文件。

Paste_Image.png

看看百度百科，ELF就是linux的可执行文件。

elf.png

2.OatDumpe查看OAT文件信息

因为youku太大了，决定不是用youku来dump，直接用个自己写的apk dump吧

haha.png

看看结果吧，好长，我就把头发出来吧，主要能够看到魔数，校验和等信息。

MAGIC:    //魔数
oat
088

LOCATION:  //位置
base.odex

CHECKSUM:  //校验和
0x116572e6

INSTRUCTION SET:  //架构
Arm64

INSTRUCTION SET FEATURES:  //指令集的特点
smp,a53

DEX FILE COUNT: //dex文件数量
1

EXECUTABLE OFFSET:  //可执行段的偏移
0x0016b000

INTERPRETER TO INTERPRETER BRIDGE OFFSET:  //不清楚，哪位大哥告诉下我
0x00000000

INTERPRETER TO COMPILED CODE BRIDGE OFFSET://不清楚，哪位大哥告诉下我
0x00000000

JNI DLSYM LOOKUP OFFSET:  //不清楚，哪位大哥告诉下我
0x00000000

QUICK GENERIC JNI TRAMPOLINE OFFSET://不清楚，哪位大哥告诉下我
0x00000000

QUICK IMT CONFLICT TRAMPOLINE OFFSET://不清楚，哪位大哥告诉下我
0x00000000

QUICK RESOLUTION TRAMPOLINE OFFSET://不清楚，哪位大哥告诉下我
0x00000000

QUICK TO INTERPRETER BRIDGE OFFSET://不清楚，哪位大哥告诉下我
0x00000000

IMAGE PATCH DELTA:   //patch的偏移
14487552 (0x00dd1000)

IMAGE FILE LOCATION OAT CHECKSUM:   //image的checksum
0x9c540d19

IMAGE FILE LOCATION OAT BEGIN:
0x71d56000

KEY VALUE STORE:
classpath = 
compiler-filter = interpret-only
debuggable = true
dex2oat-cmdline = --zip-fd=7 --zip-location=base.apk --oat-fd=9 --oat-location=/data/app/vmdl305997216.tmp/oat/arm64/base.odex --instruction-set=arm64 --instruction-set-variant=cortex-a53 --instruction-set-features=default --runtime-arg -Xms64m --runtime-arg -Xmx512m --compiler-filter=interpret-only --swap-fd=10 --debuggable
dex2oat-host = Arm
has-patch-info = false
image-location = /data/dalvik-cache/arm64/system@[email protected]:/data/dalvik-cache/arm64/system@[email protected]:/data/dalvik-cache/arm64/system@[email protected]:/data/dalvik-cache/arm64/system@[email protected]:/data/dalvik-cache/arm64/system@[email protected]:/data/dalvik-cache/arm64/system@[email protected]:/data/dalvik-cache/arm64/system@[email protected]:/data/dalvik-cache/arm64/system@[email protected]:/data/dalvik-cache/arm64/system@[email protected]:/data/dalvik-cache/arm64/system@[email protected]:/data/dalvik-cache/arm64/system@[email protected]:/data/dalvik-cache/arm64/system@[email protected]:/data/dalvik-cache/arm64/system@[email protected]:/data/dalvik-cache/arm64/system@[email protected]:/data/dalvik-cache/arm64/system@[email protected]:/data/dalvik-cache/arm64/system@[email protected]:/data/dalvik-cache/arm64/system@[email protected]:/data/dalvik-cache/arm64/system@[email protected]
native-debuggable = false
pic = false

SIZE:   //大小
1631156

APK只写了一个MainActivity，看看dump的信息是怎么描述他的

MainActivity.png

主要包含 DEX CODE，OatMethodOffsets， QuickMethodFrameInfo， CODE信息。
786: Lcom/example/anrdemo/MainActivity; (offset=0x00159fd0) (type_idx=1440) (StatusVerified) (OatClassSomeCompiled)
  0: void com.example.anrdemo.MainActivity.() (dex_method_idx=10597)
    DEX CODE:
      0x0000: 7010 1700 0000            | invoke-direct {v0}, void android.app.Activity.() // method@23
      0x0003: 7300                      | return-void-no-barrier
    OatMethodOffsets (offset=0x00000000)
      code_offset: 0x00000000 
    OatQuickMethodHeader (offset=0x00000000)
      vmap_table: (offset=0x00000000)
    QuickMethodFrameInfo
      frame_size_in_bytes: 0
      core_spill_mask: 0x00000000 
      fp_spill_mask: 0x00000000 
      vr_stack_locations:
        ins: v0[sp + #8]
        method*: v1[sp + #0]
        outs: v0[sp + #8]
    CODE: (code_offset=0x00000000 size_offset=0x00000000 size=0)
      NO CODE!
  1: void com.example.anrdemo.MainActivity.onCreate(android.os.Bundle) (dex_method_idx=10600)
    DEX CODE:
      0x0000: 6f20 2b00 5400            | invoke-super {v4, v5}, void android.app.Activity.onCreate(android.os.Bundle) // method@43
      0x0003: 1501 037f                 | const/high16 v1, #int +2130903040 // 0x7f030000
      0x0005: e920 7b01 1400            | invoke-virtual-quick {v4, v1},  // vtable@379
      0x0008: e910 3800 0400            | invoke-virtual-quick {v4},  // vtable@56
      0x000b: 0c01                      | move-result-object v1
      0x000c: 1a02 6013                 | const-string v2, "android_id" // string@4960
      0x000e: 7120 ad03 2100            | invoke-static {v1, v2}, java.lang.String android.provider.Settings$Secure.getString(android.content.ContentResolver, java.lang.String) // method@941
      0x0011: 0c00                      | move-result-object v0
      0x0012: 1a01 be29                 | const-string v1, "wenfeng" // string@10686
      0x0014: 2202 de05                 | new-instance v2, java.lang.StringBuilder // type@1502
      0x0016: 1a03 f212                 | const-string v3, "android id = " // string@4850
      0x0018: 7020 032a 3200            | invoke-direct {v2, v3}, void java.lang.StringBuilder.(java.lang.String) // method@10755
      0x001b: e920 4e00 0200            | invoke-virtual-quick {v2, v0},  // vtable@78
      0x001e: 0c02                      | move-result-object v2
      0x001f: e910 0700 0200            | invoke-virtual-quick {v2},  // vtable@7
      0x0022: 0c02                      | move-result-object v2
      0x0023: 7120 e125 2100            | invoke-static {v1, v2}, int android.util.Log.i(java.lang.String, java.lang.String) // method@9697
      0x0026: 7300                      | return-void-no-barrier
    OatMethodOffsets (offset=0x00159fdc)
      code_offset: 0x00000000 
    OatQuickMethodHeader (offset=0x00181c60)
      vmap_table: (offset=0x00163b05)
        quickened data
    QuickMethodFrameInfo
      frame_size_in_bytes: 0
      core_spill_mask: 0x00000000 
      fp_spill_mask: 0x00000000 
      vr_stack_locations:
        locals: v0[sp + #4294967276] v1[sp + #4294967280] v2[sp + #4294967284] v3[sp + #4294967288]
        ins: v4[sp + #8] v5[sp + #12]
        method*: v6[sp + #0]
        outs: v0[sp + #8] v1[sp + #12]
    CODE: (code_offset=0x00000000 size_offset=0x00181c70 size=0)
      NO CODE!

3.魔数

所谓魔数就是文件头四个字节用来记录文件类型的，是elf，还是jpg，rar之类的。我们可以用二进制查看器查看下这个oat文件。

魔数.png

可以看到前四个字节是 7f 45 4c 46，Ascii码就是 ELF。

我们看下压缩包文件的二进制，也可以看到头部是RAR

RAR