[Lazarus] Debugging the unicode RTL

Martin Frb lazarus at mfriebe.de
Sun Jan 22 11:24:08 CET 2023

On 12/01/2023 10:42, Michael Van Canneyt via lazarus wrote:
> - Debugging programs works in general quite OK, except for displaying of
>   some strings. Most notable, the exception message is affected:
>   only the first character of the exception message is shown.

This is hardcoded, and may be change-able, if debug info is avail.....

With a look at the next paragraph below....
     Exception = class .... end
  is available (ideally within the correct unit, so the debugger can 
distinguish it from some user declared type), then the debugger could 
use this.

Ideally it will by in unit system/sysutils.

On Linux, such symbols are referenced cross units. But on Windows they 
are repeated in every unit using them. That again makes it harder to 
know if it is the correct type (since the user may have its own type by 
the name).

> But for debugging this is not enough: I think the IDE debugger needs 
> another mechanism to determine using whether a program uses a unicode 
> RTL or not. The way this happens in code is {$IF SIZEOF(CHAR)=2}

I don't think the debugger should have or need such a "global" flag.

Currently if it looks at a string (and there is dwarf debug info), then 
the dwarf contains the size-of-char: 1 or 2.
And the debugger does utf8 or utf16 (the latter may be buggy).

Joost even added code to read the hidden encoding field of strings.

Though this relies on being able to detect
    PChar  <>  String  <>  array of char
which is a PITA.

> 1/ Should the compiler provide some symbol in - say - the system unit 
> to deterine
> whether the RTL is compiled in unicode mode, or is another mechanism
> preferred to do this ?
I don't think that is useful.
Better find the individual places that go wrong, and fix them.

As I said, Exceptions are hardcoded (and IIRC not even in FpDebug, but 
in LazDebuggerFp).
They could/should first search for the type "Exception"

> 2/ Where can I find the code that extracts the message from an exception
> object ? So I can have a shot at trying to fix the display.

unit FpDebugDebugger;
procedure TFpDebugDebugger.HandleSoftwareException

// Get address of object

   if not 
     SizeVal(SizeOf(AnExceptionObjectLocation)), AnExceptionObjectLocation)

     ExceptionMessage := 

That currently does not yet have the read of the "encoding" field.

What about:

is that utf16 too?
Because the debugger reads it for automatic class casting

Any other changes in the RTTI where things switched to 16 bit?

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