When are global static const variables being initialized?

Question

Hello all, I tried to search the site for this question but didn't find this exactly, although this subject is being discussed a lot...

I have this declaration in a cpp file, not within any function:

static const char* gText = "xxxxxxxxxxx";

Although it has a fixed size, I get a warning from a static analysis tool (Klocwork) when I'm trying to copy it to another char* variable - about possible out of bounds violation:

char xText[32];
SecureZeroMemory(xText, 32);
memcpy(xText, gText, strlen(gText));

Is it a false positive or is the global variable being initialized later?

Thanks!

Answer 1

It looks to be a false positive.

Answer 2

It is a false positive. strlen is probably abstracted as returning an unknown positive number, so that when analyzing the pattern memcpy(dest,src,strlen(src)); the analyzer does not realize that the reading part of the copy is safe as soon as src is a well-formed string.

If you were using strcpy, the analyzer would probably conclude that it's okay in this case. Do you have a reason not to? The function strcpy is considered "unsafe" but your memcpy(..,src,strlen(src)) is quite unsafe too.

EDIT: Also, sellibitze raises a very good point in the comments: the const attribute in the original code only applies to the chars pointed by gText and not to gText itself.

Answer 3

I would argue it is not a false positive. There is a potential risk that somebody could come along and change the length of gText without realising that it cannot be over 32 characters. I would definitely put some sort of check in before the memcpy to make sure there cannot be a buffer overrun.

e.g.

char xText[32];
SecureZeroMemory(xText, 32);
size_t lenToCopy = MIN(strlen(gText), 32);
memcpy(xText, gText, lenToCopy);

Also I'd replace the magic number 32 with a constant.