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 uppercase 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 its name all uppercase.
As an example, if you want to watch the value of a loop variable count, you should
type
watch COUNT
Or if you want to stop when a certain function (e.g MyFunction) is called, type
break MYFUNCTION
-
2.
- gdb does not know sets.
-
3.
- gdb doesn’t know strings. Strings are represented in gdb as records with a length field and an
array of char containing 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 E.
-
4.
- 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 you could
stop at it by using:
break TPOINT__DRAW
-
5.
- Global overloaded functions confuse gdb because they have the same name. Thus
you cannot set a breakpoint at an overloaded function, unless you know its line
number, in which case you can set a breakpoint at the starting line number of the
function.