Caveats when debugging with gdb

There are some peculiarities of Free Pascal which you should be aware of when using gdb. We list the main ones here:

1. Free Pascal generates information for GDB in uppercare letters. This is a consequence of the fact that pascal is a case insensitive language. So, when referring to a variable or function, you need to make it's name all uppercase.

   As an example, of you want to watch the value of a loop variable count, you should type

   watch COUNT

   Or if you want stop when a certain function (e.g MyFunction) is called, type

   break MYFUNCTION

2. Line numbers may be off by a little. This is a bug in Free Pascal and will be fixed as soon as possible.
3. gdb does not know sets.
4. gdb doesn't know strings. Strings are represented in gdb as records with a length field and an array of char contaning the string.

   You can also use the following user function to print strings:

   define pst
   set $pos=&$arg0
   set $strlen = {byte}$pos
   print {char}&$arg0.st@($strlen+1)
   end
   
   document pst
     Print out a Pascal string
   end

   If you insert it in your gdb.ini file, you can look at a string with this function. There is a sample gdb.ini in appendix F.
5. Objects are difficult to handle, mainly because gdb is oriented towards C and C++. The workaround implemented in Free Pascal is that object methods are represented as functions, with an extra parameter this (all lowercase !) The name of this function is a concatenation of the object type and the function name, separated by two underscore characters.

   For example, the method TPoint.Draw would be converted to TPOINT__DRAW, and could be stopped at with

   break TPOINT__DRAW

6. Global overloaded functions confuse gdb because they have the same name. Thus you cannot set a breakpoint at an overloaded function, unless you know it's line number, in which case you can set a breakpoint at the starting linenumber of the function.