wrong variable value from debugger on x64

[George2]

Hello everyone,


The command dv is not print the correct value for input parameters? Here is my WinDbg debug on x64 platform and source code. Any ideas about how to retrieve the correct value?

0:000> bp foo
0:000> bl
 0 e 00000001`40001020     0001 (0001)  0:**** Test64bitDebug!foo
0:000> g
Breakpoint 0 hit
Test64bitDebug!foo:
00000001`40001020 89542410        mov     dword ptr [rsp+10h],edx ss:00000000`0012fea8=cccccccc
0:000> dv
              a = -858993460
              b = -858993460


int foo (int a, int b)
{
	return a+b;
}

int main()
{
	int a1 = 100;
	int b1 = a1 + 100;

	foo (a1, b1);

	return 0;
}

thanks in advance,
George

[matsp]

The value -858993460 is 0xCCCCCCCC, which is the standard fill pattern for "unused memory" in Visual Studio, so you are seeing the variable before it's been set. Possibly because the debugger is confused about where the variable actually resides, as argument passing x64 is register, but it may be (looking at the disassembly shown for your breakpoint, I think it's likely) that the debug version of code stores local variables on the stack to make them more easily debuggable. If you step a few instructions into the code, does it work better?

--
Mats