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Andrew · Guest

Hi,

Using BCB6 enterprise update 4 and Win2K SP4.

I have a problem with an app I have made, it is the server of the
client/server system I created, when I run either the client within the IDE
and the server outside the IDE, or both apps outside the IDE I get an error
"Exception occured", this exception is occuring within the server app.

So I run the server app from the IDE and I never get any exceptions, all
runs perfectly fine apart from one thing, when I perform a certain action
(canceling an alarm) the IDE halts as though a breakpoint had been
encountered and I need to press F9 to resume, the CPU window is shown and
the following can be seen:

.....
.....
77FA144C C3 ret
ntdll.DbgUserBreakPoint:
77FA144D CC int 3
.....
.....

This does not reference any specific line of code I have written so I can go
to it, and stepping thruogh seems to take me nowhere in my code.

It would appear there is somehow a breakpoint within my code, I can look in
the breakpoint list within Builder and no breakpoints are shown. I tried
deleteing all the object files and the .TDS files and performing a complete
build of every app and DLL within the project group but still the above
breakpoint remains. Since I cannot get the server to fail during debuging I
can only assume that this is causing a problem somehow ????

Has anyone seen this before, if so how do I get rid of it and why does it
happen?

TIA

Andrew

Maurice Barnum · Guest

OBones · Guest

Maurice Barnum wrote:

Andrew · Guest

Hi,

Thanks for your replies, I have been searching the internet for this type of
problem and I found the following piece of code. It was originally in Delphi
so I ported it accross to Builder, I found it on www.howtodothings.com . It
seems that these breakpoints were left in the the microsoft DLL ntdll.dll by
accident, this function dynamically overwrites the int 3 instruction with a
NOP instruction, I have now found my problem and am very happily continueing
with my work. I hope this helps other people who have the same problem I
did....

void __fastcall TMainForm::PatchInt3(void)
{
unsigned char NOP;
DWORD BytesWritten;
HMODULE NtDll;
FARPROC P;
unsigned char szBuf[10];

if (Win32Platform != VER_PLATFORM_WIN32_NT)
return;

NtDll = GetModuleHandle("NTDLL.DLL");
if (NtDll == NULL)
return;

P = GetProcAddress(NtDll, "DbgBreakPoint");
if (P == NULL)) then
return;

try
{
if(ReadProcessMemory(GetCurrentProcess(),P,&szBuf[0],1,NULL))
{
if(szBuf[0] != 0xcc)
return;

NOP = 90;

if(WriteProcessMemory(GetCurrentProcess(),P,&NOP,1,&BytesWritten))
{
if (BytesWritten == 1)
FlushInstructionCache(GetCurrentProcess(),P,1);
}
}
}
catch(...)
{
// an exception may be raised here but don't worry about it
}
}

Thanks

Andrew

Maurice Barnum · Guest