On Sat, 5 Dec 2015, Rasmus Villemoes wrote:
> I did a search for code doing > > s[n]printf(buf, "...", ..., buf, ...) > > and found a few instances. They all do it with the format string > beginning with "%s" and buf being passed as the corresponding parameter > (obviously to append to the existing string). That works (AFAICT), both > with the current printf implementation and with the string() > modification which is now in -mm. It would obviously go horribly wrong > if anything, even non-specifiers, precede the "%s" in the format > string. > > The question is, do we want to officially support this particular case of > overlapping src and dst? Or should we close our eyes and hope it will > continue to work [1] and that it won't cause a caffeine-deprived hacker > to accidentally think one could also prepend to a buffer by doing > sprintf(buf, "...%s", ..., buf)? I'm actually surprised gcc doesn't warn > about this. > > [1] Not that I can immediately think of a sane way to implement snprintf > where it won't work, but you never know... > > My coccinelle-fu isn't sufficient to find cases where one of the buf > instances is a more complicated expressions involving buf as a > subexpression, as in > > s[n]printf(buf, "...", ..., buf + 4, ...) > > or > > s[n]printf(&buf[len], "...", ..., buf, ...) > > which would presumably always be wrong. Julia? If you just want an argument expression that contains buf somewhere, you can write <+...buf...+>. julia -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
