Debugging - GDB tricks

General tricks

• Some pascal specific patches were accepted into GDB, 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 in their raw form, 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/backtrace?
• 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

Pointer

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 its C heritage in that case:

 p ^myvartype(ptrvar)^