Debugging - GDB tricks

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Revision as of 08:35, 3 September 2010 by Chronos (talk | contribs)

General tricks

  • Some pascal specific patches were excepted; so if possible set language to pascal "set language pascal"
  • To get help, use "help <command>" or "help" to see a category list.
  • To view datastructures raw, use the "x" command (see "help x")

Examining Type Info

  • Q: What function should I use for dumping the type info?
  • A: Run x/100c in gdb until it frames. then use 'frame <framenr>' to jump to the correct frame

Inspecting an ansistring

  • Q: How do I examine an ansistring?
  • A: "x/s <stringname>"

Stop debugger on exception

  • Q: How to stop gdb on exception
  • A: b fpc_raiseexception
  • Q: How to show call stack
  • A: bt

Work with breakpoints

  • Add: b TObject__Method or b filename.pas:123
  • Show: inf b
  • Disable: dis 1
  • Enble: en 1
  • Delete: d 1
  • Delete all: d b


when you print the value of a pointer gdb will say something like:

 $0 = (MYPTR) 0x0202

If MYPTR is the correct type, you can just use

 p ptrvar^

if it's not the correct type, you can typecast it:

 p realptrtype(ptrvar)^

If you do not have a separate type for the actual pointer type, but only a type for what it points to, then the syntax is somewhat awkward because the gdb parser is still showing it's C-heritage in that case:

 p ^myvartype(ptrvar)^