[DUG] How to find Access Violation in the Initilization of Project

[Jolyon Direnko-Smith]

There's no such thing as a "$C0000005 access violation" as such.  What you
have is an access violation with the $C0000005 address involved.  That
address could be the location in memory of the instruction at which the AV
occurred, or it could be the address of the memory than an instruction
attempted to access.

The difference is important and can help identify the problem but it's
difficult to say which address this represents from the way you describe it.

A typical AV exception will read something like "Access violation at
$AAAAAAAA attempting to read/write/access address $MMMMMMMM".

$AAAAAAAA is rarely of any use, although if you are very lucky you can use
it with "Goto address" in the IDE to take you to the line of source code
corresponding to that address.  To do that the debug build in the IDE has
to be IDENTICAL to the build in which the AV occurs, and the build needs to
be running, but "paused" under the IDE.  If the build isn't identical then
the source code you find at that address is unlikely to be the actual
instruction at which the AV occurred, and even if the buid is identical it
isn't always reliable (though I've never quite figured out why).

The value of $MMMMMMMM is usually more useful and can be a first indicator
of what's going wrong.  e.g. if the problem is a NIL object reference or
pointer than $MMMMMMMM will be $00000000 (nil).  If it is an extremeley low
value such as $00000004 or $00000012 etc, then this too indicates a nil
pointer or object reference, where the actual memory access is at some
offset from the nil pointer.  e.g. a property or member variable reference
using a nil object or an array access using a nil pointer.  The lower the
value, the more likely it is to be a member variable reference.

If $MMMMMMMM is anything significantly greater than nil then this usually
indicates an uninitialized pointer or an access to an already destroyed
object.


Other than that, if the problem is occurring during initialization then you
need to find all your initialization sections and debug those.  But this
will be harder if the problem is in an RTL or VCL unit.  You will need to
compile with Use Debug DCU's enabled, but if you do that and can reproduce
the AV under the debugger then all you should need to do is run the build
under the debugger.

Make sure that "Break on exceptions" is enabled in the debugger and also
that EAccessViolation is not on the "ignore" list in the debugger options.


Hope that helps.

On 10 April 2017 at 10:09, Todd Martin <todd.martin.nz at gmail.com> wrote:

> Hi Ian
>
> Search through all the files in your project and look for the
> *initialization* keyword. Put a break point wherever you find code. Then
> run the application and see where it dies.
>
> On 10 Apr 2017 6:56 a.m., "Ian Fear" <I_J_Fear at xtra.co.nz> wrote:
>
>> I am in the process of Moving a Project from D2007 to D XE10 berlin.
>>
>> After some grief I have the Project Compiling in XE10.
>>
>> When the project loads I Get a $C0000005 access violation in the Projects
>> Initialization section before I get to any breakpoints on main form Create
>> etc
>>
>>
>>
>> On following it thru the CPU window it Happens at vcl.AxCtls  or  4 lines
>> later Tpicture.loadFileFormats
>>
>> Would appreciate any hints on how to track this down. It May be trying to
>> call in a FMX unit but cant figure out how to track it Down
>>
>>
>>
>> Any Hints or suggestions greatly appreciated
>>
>>
>>
>> Thanks in advance
>>
>> Regards
>>
>> Ian
>>
>>
>>
>> Ian Fear
>>
>> B Agr Sc (Lincoln)
>>
>> GDip InfSys(Massey)
>>
>>
>>
>> Fear Consulting Ltd
>>
>> 405 Old Taupo Road
>>
>> Rotorua
>>
>> Home /work 07 347 6015
>>
>> Mobile 027 474 2772
>>
>>
>>
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