Portable and non-deletable breakpoint

[MarkMLl]

Is there an approved way of putting something in a program which will act as a breakpoint if run under a debugger but is otherwise ignored? I don't really want to use Assert(false) since that will always raise an exception.

The scenario is that I've got a fork of some old code I'm modernising gradually, it runs OK standalone but I want to mark the place I'm currently working on so that it's immediately apparent in the (Lazarus etc.) IDE. I don't want to use a standard breakpoint since this can obviously be cleared by the IDE, irrespective of any dire warnings in the source.

Yesterday evening I caused myself much headscratching when I put a breakpoint on a valid line but it didn't actually trigger, at which point control headed off into (what I should have remembered was) Terra Incognita.

MarkMLl

[440bx]

From your posts, I suspect you want a cross platform solution.

First, I'll mention the Windows-only solution which is use IsDebuggerPresent() followed by an int 3.  Code like this:

Code: Pascal  [Select][+][-]

1. if IsDebuggerPresent() then asm int 3 end;

Quite simple but, unfortunately Windows only.

I presume there has to be a way under other operating systems (commonly Linux) to determine if a program is being debugged, if so, just implement your own version of IsDebuggerPresent() for that platform and problem solved.

HTH.

[MarkMLl]

@440bx The int can be easily replaced by an Assert(false). I was pretty sure I'd seen this discussed (multiple times) before, and Google points me at https://forum.lazarus.freepascal.org/index.php?topic=46981.0 where Thaddy suggests a Linux hack via /proc... I'll experiment and report back but can't test behaviour on Mac etc.

MarkMLl

[MarkMLl]

This works nicely under Linux:

Code: Pascal  [Select][+][-]

1. {$if not declared(IsDebuggerPresent)    }
2.  
3. function grep(caseInsensitive: boolean; const pattern, fn: ansistring): ansistring;
4.  
5. var
6.   scratch: TStringList;
7.   i: integer;
8.  
9. begin
10.   result := '';
11.   if not FileExists(fn) then
12.     exit;
13.   scratch := TStringList.Create;
14.   try
15.     scratch.LoadFromFile(fn);
16.     for i := 0 to scratch.Count - 1 do
17.       if caseInsensitive then begin
18.         if AnsiContainsText(scratch[i], pattern) then
19.           exit(scratch[i])              (* Via finally                          *)
20.       end else
21.         if AnsiContainsStr(scratch[i], pattern) then
22.           exit(scratch[i])              (* Via finally                          *)
23.   finally
24.     scratch.Free
25.   end
26. end { grep } ;
27.  
28.  
29. function isDebuggerPresent(): boolean;
30.  
31. var
32.   scratch: ansistring;
33.  
34. begin
35.   scratch := grep(true, 'TracerPid', '/proc/' + IntToStr(GetProcessID()) + '/status');
36.  
37. (* TracerPid has existed since at least late Linux kernel 2.x, as of 2021 it's  *)
38. (* unreasonable to expect Lazarus/FPC to be running on anything older and while *)
39. (* the /proc tree might be supressed on embedded systems this is unlikely to be *)
40. (* the case on a system that might have a debugger on it. Having no TracerPid   *)
41. (* can reasonably be interpreted as there being no active debugger, but it is   *)
42. (* still necessary to check that it is non-zero.                                *)
43.  
44.   if scratch = '' then
45.     result := false
46.   else begin
47.     scratch := DelSpace(Tab2Space(scratch, 1));
48.     result := Pos(':0', scratch) <> Length(scratch) - 1
49.   end
50. end { isDebuggerPresent } ;
51.  
52. {$endif not declared(IsDebuggerPresent) }
53.  
54. ...
55.   if IsDebuggerPresent() then // Non-continuable forced breakpoint
56.     Assert(false);
57.  
58.   if IsDebuggerPresent() then // Continuable forced breakpoint
59.     try Assert(false, 'Terra Incognita (here be dragons!)') except end;
60.  

Google suggests that Solaris/SunOS has something comparable but not in the same place. Can anybody speak for Macs and the BSDs?

MarkMLl