Debugging Go Code with GDB

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1. Debugging Go Code with GDB kaneshin Go Conference 2015 summer
2. Shintaro Kaneko (kaneshin) - Senior Engineer @ eureka kaneshin kaneshinth shintaro.kaneko
4. What is eureka?
5. How do you Debug Go code?
6. Print Debugging?
7. func  main()  {     v  :=  map[string]string{"key":  "value"}     fmt.Println("DEBUG",  v)     for  _,  d  :=  range  v  {       ..     }   }
8. func  main()  {     v  :=  map[string]string{"key":  "value"}     fmt.Println("DEBUG",  v)     for  _,  d  :=  range  v  {       ..     }   }
10. The Disadvantages of Print Debugging fmt.Print
11. Ad-hoc Code is temporarily added
12. func  main()  {     v  :=  map[string]string{"key":  "value"}     for  _,  d  :=  range  v  {       ..     }   } If problems occur
13. func  main()  {     v  :=  map[string]string{"key":  "value"}     fmt.Println("DEBUG",  v)     for  _,  d  :=  range  v  {       ..     }     fmt.Println("DEBUG",  v)   } Add code temporarily
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
16. Lost buffer in case of a crash
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
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
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)
21. Can’t interrupt processing program
22. func  main()  {     v  :=  map[string]string{"key":  "value",  ..}     for  _,  d  :=  range  v  {       ..       ..     }   } If problems occur
23. func  main()  {     v  :=  map[string]string{"key":  "value",  ..}     for  _,  d  :=  range  v  {       ..       fmt.Println("DEBUG",  d)       ..     }   } Add code temporarily
24. DEBUG  value   DEBUG  ..   DEBUG  ..   DEBUG  ..   DEBUG  ..   DEBUG  ..   DEBUG  ..   DEBUG  ..   DEBUG  ..   DEBUG  ..   DEBUG  ..   The Stream of the log..
26. No more!
27. Do you debug with GDB, don’t you?
28. The Advantages of GDB over Print Debugging
29. Printable Variables directly Doesn’t need to add temp code
30. Interruptible/Attachable processing program
31. Remote debugging
32. How to execute GDB?
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)
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`
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*
36. $ gdb main.go to execute GDB
37. I’m not talking about How to USE gdb I will if there is a next time
38. ͜͜·Ͱத൫ ͪΐͬͱ͚ͩ೔ຊޠ͕ग़͖ͯ·͢
39. Struggled with GDB
40. 1. Broken DWARF 2. An old GDB is in my GDB 3. Runtime Bug (runtime.py) 4. Web Application Framework: Revel
41. 1. Broken DWARF
42. Broken DWARF ‣ Go 1.4+͸मਖ਼ࡁΈ ‣ Go 1.3.x Ͱ͸ਖ਼͍͠஋͕දࣔ͞Εͳ͍
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)
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)
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)
46. 2. An old GDB is in my MBA
47. 2. An old GDB is in my MBA ‣ Actually it was my fault. ‣ Be careful if you will install GDB
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
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  
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)  
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)  
52. 2. An old GDB is in my MBA    $  which  gdb      /usr/bin/gdb  
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  
54. 3. Runtime Bug
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  <module>          _rctp_type  =  gdb.lookup_type("struct  runtime.rtype").pointer()   gdb.error:  No  struct  type  named  runtime.rtype.
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  <module>          _rctp_type  =  gdb.lookup_type("struct  reflect.rtype").pointer()   gdb.error:  No  struct  type  named  runtime.rtype.
57. 4. WAF: Revel
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
59. GDBͱͷ૬ੑѱ͘ͳ͍Ͱ͔͢ʁ
60. GDBͱͷ૬ੑѱ͘ͳ͍Ͱ͔͢ʁ ͦ΋ͦ΋ɺGoͷGDBαϙʔτ͕ऑ͍͔ΒͶ
61. GDBͱͷ૬ੑѱ͘ͳ͍Ͱ͔͢ʁ ͦ΋ͦ΋ɺGoͷGDBαϙʔτ͕ऑ͍͔ΒͶ revelʹ͸ revel.DEBUG.Printf ͱ͍͏ૉ੖Β͍͠ Printؔ਺͕͋Δ͔Β
62. Printσόοάͯ͠Ͷˑ
65. OK, RevelͰGDBఘΊΔΘ
66. ·ͱΊ ‣ Print Debugging͸΍Ίͨ΄͏͕͍͍͚Ͳ… ‣ GDBͱGo͸·ͩൃల్্ ‣ ਖ਼௚Ϗϧυ͕଎͍ ‣ Web Application ͱ૬ੑ͕ѱ͍
67. ·ͱΊ ‣ Print Debugging͸΍Ίͨ΄͏͕͍͍͚Ͳ… ‣ GDBͱGo͸·ͩൃల్্ ‣ ਖ਼௚Ϗϧυ͕଎͍ ‣ Web Application ͱ૬ੑ͕ѱ͍ ‣ RevelΛ૬౰͍͡Γ·ͨ͠ɻ͕ɺRevelͷ։ൃ͕ਐΉͷ͕ਏ͍
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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