Debugging Go Code with GDB

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1. Debugging Go Code with GDB
   kaneshin
   Go Conference 2015 summer
   

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2. Shintaro Kaneko (kaneshin)
   - Senior Engineer @ eureka
   kaneshin
   kaneshinth
   shintaro.kaneko
   

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4. What is eureka?
   

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5. How do you Debug Go code?
   

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6. Print Debugging?
   

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7. func  main()  {  
     v  :=  map[string]string{"key":  "value"}  
     fmt.Println("DEBUG",  v)  
     for  _,  d  :=  range  v  {  
       ..  
     }  
   }
   

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8. func  main()  {  
     v  :=  map[string]string{"key":  "value"}  
     fmt.Println("DEBUG",  v)  
     for  _,  d  :=  range  v  {  
       ..  
     }  
   }
   

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9. View Slide

10. The Disadvantages of
    Print Debugging
    fmt.Print
    

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11. Ad-hoc
    Code is temporarily added
    

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12. func  main()  {  
      v  :=  map[string]string{"key":  "value"}  
      for  _,  d  :=  range  v  {  
        ..  
      }  
    }
    If problems occur
    

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13. func  main()  {  
      v  :=  map[string]string{"key":  "value"}  
      fmt.Println("DEBUG",  v)  
      for  _,  d  :=  range  v  {  
        ..  
      }  
      fmt.Println("DEBUG",  v)  
    }
    Add code temporarily
    

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14. func  main()  {  
      v  :=  map[string]string{"key":  "value"}  
      //  fmt.Println("DEBUG",  v)  
      for  _,  d  :=  range  v  {  
        ..  
      }  
      //  fmt.Println("DEBUG",  v)  
    }
    Disable/Remove code as soon as solved
    

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16. Lost buffer in case of a crash
    

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17.   r,  w,  _  :=  os.Pipe()  
      os.Stdout  =  w  
      oc  :=  make(chan  string)  
      go  func()  {  
        var  buf  bytes.Buffer  
        io.Copy(&buf,  r)  
        oc  <-­‐  buf.String()  
      }()
    Pipe STDOUT
    

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18.   r,  w,  _  :=  os.Pipe()  
      os.Stdout  =  w  
      oc  :=  make(chan  string)  
      go  func()  {  
        var  buf  bytes.Buffer  
        io.Copy(&buf,  r)  
        oc  <-­‐  buf.String()  
      }()
    In case of io.Copy crash
    

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19.   r,  w,  _  :=  os.Pipe()  
      os.Stdout  =  w  
      oc  :=  make(chan  string)  
      go  func()  {  
        var  buf  bytes.Buffer  
        io.Copy(&buf,  r)  
        oc  <-­‐  buf.String()  
      }()
    Maybe you add print code..
    fmt.Println(buf)  
    fmt.Println(buf)
    

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21. Can’t interrupt processing program
    

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22. func  main()  {  
      v  :=  map[string]string{"key":  "value",  ..}  
      for  _,  d  :=  range  v  {  
        ..  
        ..  
      }  
    }
    If problems occur
    

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23. func  main()  {  
      v  :=  map[string]string{"key":  "value",  ..}  
      for  _,  d  :=  range  v  {  
        ..  
        fmt.Println("DEBUG",  d)  
        ..  
      }  
    }
    Add code temporarily
    

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24. DEBUG  value  
    DEBUG  ..  
    DEBUG  ..  
    DEBUG  ..  
    DEBUG  ..  
    DEBUG  ..  
    DEBUG  ..  
    DEBUG  ..  
    DEBUG  ..  
    DEBUG  ..  
    DEBUG  ..  
    The Stream of the log..
    

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26. No more!
    

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27. Do you debug with GDB,
    don’t you?
    

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28. The Advantages of GDB
    over Print Debugging
    

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29. Printable Variables directly
    Doesn’t need to add temp code
    

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30. Interruptible/Attachable
    processing program
    

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31. Remote debugging
    

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32. How to execute GDB?
    

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33. How to execute GDB?
    ‣ It’s very easy to debug code
    ‣ See "Debugging Go Code with GDB"
    ‣ https://golang.org/doc/gdb
    ‣ GDB debugger ver 7.1+
    ‣ To inspect a live process or a core dump from DWARF
    ‣ Go ver 1.4+
    ‣ Go v1.2~1.3.3 are not working (DWARF has been missing)
    

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34. How to execute GDB?
    ‣ Compile Go Code to contain useful debugging information
    ‣ Pass `-gcflags "-N -l"` to disable optimizations of compile
    ‣ For example: `go build -gcflags "-N -l" /path/to/repo`
    ‣ Pass `-ldflags "-w"` to omit the debug information
    ‣ For example: `go build -ldflags "-w" /path/to/repo`
    

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35. $  go  build  -­‐o  fib  github.com/kaneshin/go-­‐fibonacci                
    $  go  build  -­‐gcflags  "-­‐N  -­‐l"  -­‐o  fib-­‐none  \  
                                       github.com/kaneshin/go-­‐fibonacci    
    $  go  build  -­‐ldflags  "-­‐w"  -­‐o  fib-­‐omit  \  
                                       github.com/kaneshin/go-­‐fibonacci      
       
    $  ls  -­‐al  |  grep  fib  
    -­‐rwxr-­‐xr-­‐x      1  root  root  6452704  Jun  20  11:19  fib*  
    -­‐rwxr-­‐xr-­‐x      1  root  root  6452744  Jun  20  11:24  fib-­‐none*  
    -­‐rwxr-­‐xr-­‐x      1  root  root  5128473  Jun  20  11:19  fib-­‐omit*
    

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36. $ gdb main.go
    to execute GDB
    

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37. I’m not talking about
    How to USE gdb
    I will if there is a next time
    

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38. ͜͜·Ͱத൫
    ͪΐͬͱ͚ͩ೔ຊޠ͕ग़͖ͯ·͢
    

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39. Struggled with GDB
    

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40. 1. Broken DWARF
    2. An old GDB is in my GDB
    3. Runtime Bug (runtime.py)
    4. Web Application Framework: Revel
    

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41. 1. Broken DWARF
    

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42. Broken DWARF
    ‣ Go 1.4+͸मਖ਼ࡁΈ
    ‣ Go 1.3.x Ͱ͸ਖ਼͍͠஋͕දࣔ͞Εͳ͍
    

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43. Broken DWARF
    ‣ Go 1.4+͸मਖ਼ࡁΈ
    ‣ Go 1.3.x Ͱ͸ਖ਼͍͠஋͕දࣔ͞Εͳ͍
       num  :=  r.URL.Query().Get("num")  
       n,  err  :=  strconv.Atoi(num)  
    >  if  err  !=  nil  {  
               fmt.Fprintln(os.Stderr,  err)
    

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44. Broken DWARF
    ‣ Go 1.4+͸मਖ਼ࡁΈ
    ‣ Go 1.3.x Ͱ͸ਖ਼͍͠஋͕දࣔ͞Εͳ͍
    (gdb)  info  locals  
    val  =  833358128335  
    n  =  3  
    num  =  0xc20803e4d3  "1000"  
    err  =  {tab  =  0xc20802e170,  data  =  0xc20802e160}  
    (gdb)    
       num  :=  r.URL.Query().Get("num")  
       n,  err  :=  strconv.Atoi(num)  
    >  if  err  !=  nil  {  
               fmt.Fprintln(os.Stderr,  err)
    

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45. Broken DWARF
    ‣ Go 1.4+͸मਖ਼ࡁΈ
    ‣ Go 1.3.x Ͱ͸ਖ਼͍͠஋͕දࣔ͞Εͳ͍
    (gdb)  info  locals  
    val  =  833358128335  
    n  =  3  
    num  =  0xc20803e4d3  "1000"  
    err  =  {tab  =  0xc20802e170,  data  =  0xc20802e160}  
    (gdb)    
       num  :=  r.URL.Query().Get("num")  
       n,  err  :=  strconv.Atoi(num)  
    >  if  err  !=  nil  {  
               fmt.Fprintln(os.Stderr,  err)
    

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46. 2. An old GDB is in my MBA
    

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47. 2. An old GDB is in my MBA
    ‣ Actually it was my fault.
    ‣ Be careful if you will install GDB
    

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48. 2. An old GDB is in my MBA
    ‣ Actually it was my fault.
    ‣ Be careful if you will install GDB
    How to Install GDB on OS X (Needs to sign your certification)
       $  brew  install  homebrew/dupes/gdb
    

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49. 2. An old GDB is in my MBA
    ‣ Actually it was my fault.
    ‣ Be careful if you will install GDB
    How to Install GDB on OS X (Needs to sign your certification)
       $  brew  install  homebrew/dupes/gdb  
       $  gdb  -­‐v  
    

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50. 2. An old GDB is in my MBA
    ‣ Actually it was my fault.
    ‣ Be careful if you will install GDB
    How to Install GDB on OS X (Needs to sign your certification)
       $  brew  install  homebrew/dupes/gdb  
       $  gdb  -­‐v  
       GNU  gdb  6.3.50-­‐20050815  (Apple  version  gdb-­‐1824)  
       (Wed  Feb    6  22:51:23  UTC  2013)  
    

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51. 2. An old GDB is in my MBA
    ‣ Actually it was my fault.
    ‣ Be careful if you will install GDB
    How to Install GDB on OS X (Needs to sign your certification)
       $  brew  install  homebrew/dupes/gdb  
       $  gdb  -­‐v  
       GNU  gdb  6.3.50-­‐20050815  (Apple  version  gdb-­‐1824)  
       (Wed  Feb    6  22:51:23  UTC  2013)  
    

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52. 2. An old GDB is in my MBA
       $  which  gdb  
       /usr/bin/gdb  
    

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53. 2. An old GDB is in my MBA
       $  which  gdb  
       /usr/bin/gdb  
         
       $  `brew  -­‐-­‐prefix  gdb`/bin/gdb  -­‐v  
       GNU  gdb  (GDB)  7.9.1  
    

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54. 3. Runtime Bug
    

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55. 3. Runtime Bug
    ‣ See "gdb: No struct type named runtime.rtype #9326"
    ‣ https://github.com/golang/go/issues/9326
    gdb  main.go  -­‐d  $GOROOT  
    ...  
    (gdb)  source  /usr/local/go/src/runtime/runtime-­‐gdb.py    
    Loading  Go  Runtime  support.  
    Traceback  (most  recent  call  last):  
       File  "/usr/local/go/src/runtime/runtime-­‐gdb.py",  line  205,  in    
           _rctp_type  =  gdb.lookup_type("struct  runtime.rtype").pointer()  
    gdb.error:  No  struct  type  named  runtime.rtype.
    

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56. 3. Runtime Bug
    ‣ See "gdb: No struct type named runtime.rtype #9326"
    ‣ https://github.com/golang/go/issues/9326
    gdb  main.go  -­‐d  $GOROOT  
    ...  
    (gdb)  source  /usr/local/go/src/runtime/runtime-­‐gdb.py    
    Loading  Go  Runtime  support.  
    Traceback  (most  recent  call  last):  
       File  "/usr/local/go/src/runtime/runtime-­‐gdb.py",  line  205,  in    
           _rctp_type  =  gdb.lookup_type("struct  reflect.rtype").pointer()  
    gdb.error:  No  struct  type  named  runtime.rtype.
    

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57. 4. WAF: Revel
    

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58. 4. WAF: Revel
    ‣ Revel is kind of Web Application Framework
    ‣ See "How to debug app with GDB?" #921
    ‣ https://github.com/revel/revel/issues/921
    

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59. GDBͱͷ૬ੑѱ͘ͳ͍Ͱ͔͢ʁ
    

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60. GDBͱͷ૬ੑѱ͘ͳ͍Ͱ͔͢ʁ
    ͦ΋ͦ΋ɺGoͷGDBαϙʔτ͕ऑ͍͔ΒͶ
    

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61. GDBͱͷ૬ੑѱ͘ͳ͍Ͱ͔͢ʁ
    ͦ΋ͦ΋ɺGoͷGDBαϙʔτ͕ऑ͍͔ΒͶ
    revelʹ͸ revel.DEBUG.Printf ͱ͍͏ૉ੖Β͍͠
    Printؔ਺͕͋Δ͔Β
    

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62. Printσόοάͯ͠Ͷˑ
    

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65. OK, RevelͰGDBఘΊΔΘ
    

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66. ·ͱΊ
    ‣ Print Debugging͸΍Ίͨ΄͏͕͍͍͚Ͳ…
    ‣ GDBͱGo͸·ͩൃల్্
    ‣ ਖ਼௚Ϗϧυ͕଎͍
    ‣ Web Application ͱ૬ੑ͕ѱ͍
    

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67. ·ͱΊ
    ‣ Print Debugging͸΍Ίͨ΄͏͕͍͍͚Ͳ…
    ‣ GDBͱGo͸·ͩൃల్্
    ‣ ਖ਼௚Ϗϧυ͕଎͍
    ‣ Web Application ͱ૬ੑ͕ѱ͍
    ‣ RevelΛ૬౰͍͡Γ·ͨ͠ɻ͕ɺRevelͷ։ൃ͕ਐΉͷ͕ਏ͍
    

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68. ·ͱΊ
    ‣ Print Debugging͸΍Ίͨ΄͏͕͍͍͚Ͳ…
    ‣ GDBͱGo͸·ͩൃల్্
    ‣ ਖ਼௚Ϗϧυ͕଎͍
    ‣ Web Application ͱ૬ੑ͕ѱ͍
    ‣ RevelΛ૬౰͍͡Γ·ͨ͠ɻ͕ɺRevelͷ։ൃ͕ਐΉͷ͕ਏ͍
    ‣ GDB࢖͏ʹͯ͠΋೜଱ڧ͘ͳ͍ͱਏ͍
    

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69. Copyright © 2009-2015 eureka, Inc. All rights reserved.
    Thank you
    

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