在執行stap的時候,經常會發現在指令碼結束執行的時候打出了很多無預期的東西,仔細一看都是些全域性變數的dump, 這個問題比較煩人.

我來演示下:

$ cat > g.stp 
global xyz
probe begin{
  xyz=2010
  exit();
}
CTRL+D

$ sudo stap g.stp
xyz=0x7da
#多餘的顯示,其實我們只想靜悄悄的結束

查看了程式碼和文件發現:

A global declaration may be written at the outermost level anywhere, not
within a block of code. Global variables which are written but never read will be displayed automatically at session shutdown. The translator
will infer for each its value type, and if it is used as an array, its key types. Optionally, scalar globals may be initialized with a string or
number literal. The following declaration marks variables as global.

原來只寫不讀的通通要列印提醒你, 知道了原因就好辦了.

加多個delete把全域性變數清空,就沒啥好顯示了:

$ diff -up g1.stp g.stp 
--- g1.stp	2011-03-25 13:14:37.940594540 +0800
+++ g.stp	2011-03-25 13:12:59.470450112 +0800
@@ -1,5 +1,6 @@
 global xyz
 probe begin{
   xyz=2010
+delete xyz 
  exit();
 }

玩的開心.

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