65 lines
3.2 KiB
Markdown
65 lines
3.2 KiB
Markdown
# fieldcount
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fieldcount is a JVMTI agent designed to investigate the types being held by specific fields and
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how large the objects referenced by these fields are.
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Note that just by using the agent some fields might be written (for example fields related to
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keeping track of jfieldIDs). Users should be aware of this.
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# Usage
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### Build
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> `m libfieldcount libfieldcounts`
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The libraries will be built for 32-bit, 64-bit, host and target. Below examples
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assume you want to use the 64-bit version.
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### Command Line
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The agent is loaded using -agentpath like normal. It takes arguments in the
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following format:
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> `Lname/of/class;.nameOfField:Ltype/of/field;[,...]`
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#### ART
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```shell
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art -Xplugin:$ANDROID_HOST_OUT/lib64/libopenjdkjvmti.so '-agentpath:libfieldcount.so=Ljava/lang/Class;.extData:Ldalvik/system/ClassExt;,Ldalvik/system/ClassExt;.jmethodIDs:Ljava/lang/Object;' -cp tmp/java/helloworld.dex -Xint helloworld
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```
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* `-Xplugin` and `-agentpath` need to be used, otherwise the agent will fail during init.
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* If using `libartd.so`, make sure to use the debug version of jvmti.
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```shell
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adb shell setenforce 0
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adb push $ANDROID_PRODUCT_OUT/system/lib64/libfieldcounts.so /data/local/tmp/
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adb shell am start-activity --attach-agent '/data/local/tmp/libfieldcounts.so=Ljava/lang/Class;.extData:Ldalvik/system/ClassExt;,Ldalvik/system/ClassExt;.jmethodIDs:Ljava/lang/Object;' some.debuggable.apps/.the.app.MainActivity
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```
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#### RI
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> `java '-agentpath:libfieldcount.so=Lname/of/class;.nameOfField:Ltype/of/field;' -cp tmp/helloworld/classes helloworld`
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### Printing the Results
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All statistics gathered during the trace are printed automatically when the
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program normally exits. In the case of Android applications, they are always
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killed, so we need to manually print the results.
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> `kill -SIGQUIT $(pid com.littleinc.orm_benchmark)`
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Will initiate a dump of the counts (to logcat).
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The dump will look something like this.
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```
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dalvikvm64 I 06-27 14:24:59 183155 183155 fieldcount.cc:60] listing field Ljava/lang/Class;.extData:Ldalvik/system/ClassExt;
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dalvikvm64 I 06-27 14:24:59 183155 183155 fieldcount.cc:60] listing field Ldalvik/system/ClassExt;.jmethodIDs:Ljava/lang/Object;
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Hello, world!
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dalvikvm64 I 06-27 14:24:59 183155 183155 fieldcount.cc:97] Dumping counts of fields.
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dalvikvm64 I 06-27 14:24:59 183155 183155 fieldcount.cc:98] Field name Type Count Total Size
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dalvikvm64 I 06-27 14:24:59 183155 183155 fieldcount.cc:155] Ljava/lang/Class;.extData:Ldalvik/system/ClassExt; <ALL TYPES> 2800 3024
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dalvikvm64 I 06-27 14:24:59 183155 183155 fieldcount.cc:161] Ljava/lang/Class;.extData:Ldalvik/system/ClassExt; Ldalvik/system/ClassExt; 64 3024
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dalvikvm64 I 06-27 14:24:59 183155 183155 fieldcount.cc:161] Ljava/lang/Class;.extData:Ldalvik/system/ClassExt; <null> 2738 0
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dalvikvm64 I 06-27 14:24:59 183155 183155 fieldcount.cc:155] Ldalvik/system/ClassExt;.jmethodIDs:Ljava/lang/Object; <ALL TYPES> 63 10008
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dalvikvm64 I 06-27 14:24:59 183155 183155 fieldcount.cc:161] Ldalvik/system/ClassExt;.jmethodIDs:Ljava/lang/Object; <null> 26 0
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dalvikvm64 I 06-27 14:24:59 183155 183155 fieldcount.cc:161] Ldalvik/system/ClassExt;.jmethodIDs:Ljava/lang/Object; [J 39 10008
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```
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