On Thu, Jun 07, 2018 at 09:47:18AM +0530, Viresh Kumar wrote: > On 06-06-18, 14:26, Steven Rostedt wrote: > > On Wed, 6 Jun 2018 16:26:00 +0200 > > Johan Hovold <johan@xxxxxxxxxx> wrote: > > > > > Looks like the greybus code above is working as intended by checking for > > > unterminated string after the strncpy, even if this does now triggers > > > the truncation warning. > > So why exactly are we generating a warning here ? Is it because it is possible > that the first n bytes of src may not have the null terminating byte and the > dest may not be null terminated eventually ? Yes, new warning in GCC 8: https://gcc.gnu.org/onlinedocs/gcc-8.1.0/gcc/Warning-Options.html#index-Wstringop-truncation > Maybe I should just use memcpy here then ? No, as you note below, you use strncpy to clear the rest of the buffer. > But AFAIR, I used strncpy() specifically because it also sets all the remaining > bytes after the null terminating byte with the null terminating byte. And so it > is pretty easy for me to check if the final string is null terminated by > checking [max - 1] byte against '\0', which the code is doing right now. > > I am not sure what would the best way to get around this incorrect-warning. It seems gcc just isn't smart enough in this case (where you check for overflow and never use a non-terminated string), but it is supposed to detect when the string is unconditionally terminated. So perhaps just adding a redundant buf[size-1] = '\0' before returning in the error path or after the error path would shut it up. But that's a bit of a long shot, I admit. Probably best to leave things as they are, and let the gcc folks find a way to handle such false positives. Thanks, Johan -- To unsubscribe from this list: send the line "unsubscribe linux-kbuild" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
