Setting a value in the debugger of a shared section

Question

I have the following code in a DLL:

 #pragma data_seg("ABC")
 __declspec (dllexport) char abc[2000] = { 0 };
 #pragma data_seg()
 #pragma comment(linker, "-section:ABC,rws")

I have the following code in an executable:

extern "C" __declspec(dllimport) char abc[];
char *abcPtr = abc;
#define iVar0 (*(long *)(abcPtr))

int main()
{
    printf("Value: %d %p\n", iVar0, &iVar0);
    iVar0 = 66;
    printf("Value: %d %p\n", iVar0, &iVar0);

    char buffer[256];
    scanf_s("%s", buffer, 256);
}

When I run the first instance of the program I get:

Value: 0 0FC2A000
Value: 66 0FC2A000

If I run a second instance I get the following because they are using the same shared section:

Value: 66 0FC2A000 <- Notice the value here is set
Value: 66 0FC2A000

However if I change the value in the first instance using Visual Studio debugger, I can see that it changed in the memory location; however, I cannot see the value change if I rerun the second instance.

Why is the debugger not able to write the actual shared (memory) section?

Answer 1

I got the same result as yours:

My understanding is that certain value was not shared in the shared memory during debugging.

https://blogs.msdn.microsoft.com/oldnewthing/20040804-00/?p=38253/