How debug and don't stop on hardware exceptions
lazarus / 12-Debugger

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Borneq · 2012-12-14 23:01

I analyze exceptions in FreePascal. I begin to understand software
exceptions caused by raise, but no hardware like dividing by zero.
When I debug my debug process has stopped.
- how debug?
- how FreePascal works with hardware exceptions?

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Martin_fr · 2012-12-14 23:26

Unfortunately this is a problem within GDB. Something that can not be
fixed in Lazarus.

http://wiki.lazarus.freepascal.org/GDB_Debugger_Tips#SigSegV_-
_and_continue_debugging

http://wiki.lazarus.freepascal.org/GDB_Debugger_Tips#Hardware_exceptio
ns_under_Mac_OS_X

If you have floating point, you can somehow specify that no exception
is triggered (unit math). But otherwise, I do not know any solution,
except for changing the code.

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Borneq · 2012-12-14 23:41

Quote from: Martin_fr on December 15, 2012, 12:26:50 amIf you have
floating point, you can somehow specify that no exception is triggered
(unit math). But otherwise, I do not know any solution, except for
changing the code.
Hardware exceptions is needed but how FreePascal handle it? He not use
Structured Exeptions Handling provided with Windows but use own
method. How can catch system signal ?
I attach files:
handling1.lpr - standard try-except to disassembling and debug
own_handling1.dpr - exceptions with fpc_XXX methods (for Delphi)
instead try-except sugar, work for software raise fine, but not for
hardware exceptions
Fpc_exceptions.pas - unit with functions fpc_XXX for Delphi

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Blaazen · 2012-12-15 00:25

IIRC there were some discussion on mailing list about this and Jonas
Maebe explained how it works but I cannot find the right one (there
are more threads about it).

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Borneq · 2012-12-15 00:35

Which is mailing list archive address?

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Blaazen · 2012-12-15 00:45

List of archives is here: http://www.freepascal.org/maillist.var

IIRC the mentioned thread was on the FPC-General, which is also here:
http://free-pascal-general.1045716.n5.nabble.com/

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Martin_fr · 2012-12-15 01:09

From what I remember (and it may be inaccurate)

A program can register (with the OS) a handler for hardware
exceptions. On Linux this are Signal handlers, on win I don't remember
what they are called.

FPC does set such a handler, and then in that handler, if it is
called, raises an exception.

GDB does set it's own handler, and is supposed to call the programs
(if registered) handler, in case that the user wishes to continue
after such a condition occurred.

The problem is, that at least on windows (and possible Mac) GDB can't
do that (call the original handler). Not sure if that is a problem in
GDB, IIRC I read some post it was a problem how windows works. But I
can't judge that anyway.

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Borneq · 2012-12-15 02:04

In c:\lazarus\fpc\2.6.0\source\rtl\win32\system.pp in "procedure
Exe_entry" is install_exception_handlers which call
SetUnhandledExceptionFilter(@syswin32_i386_exception_handler);
but this is not all