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SubjectRe: [PATCH] string: Improve the generic strlcpy() implementation

* Linus Torvalds <torvalds@linux-foundation.org> wrote:

> On Oct 5, 2015 14:15, "Ingo Molnar" <mingo@kernel.org> wrote:
> >
> > Hm, so GCC (v4.9.2) will only warn about this bug if -Wtype-limits is enabled
> > explicitly:
>
> Some of the warnings are really nasty, and cause people to write worse code.
>
> For example, this is inherently good code:
>
> if (x < 0 || x > MAXLEN)
> return -EINVAL;
>
> and a compiler that warns about that is pure and utter crap. Obviously. Agreed?
>
> Now, imagine that "x" here is some random type. Maybe it's s "char" and you
> don't even know the sign. Maybe it's "loff_t". Maybe it's "size_t", or whatever.
>
> Note how that test is correct *regardless* of the sign of the type. A compiler
> that warns about the "x < 0" part just because x happens to be unsigned is a bad
> bad compiler, and makes people remove that check, even though it's good for
> readability, and good for robustness wrt changing the type.

Yeah, that's true.

> We really do have types where sightedness depends on architecture or
> possibly configuration options. "char" is the obvious example, but the type
> limit can matter too: on some architectures you might have a type that is
> 16 bits, on another it might be 32 bits. Do you really think that
>
> if (x > 65535)
> return -E2BIG;
>
> should have some #ifdef __xyz__ around it just because the compiler warns
> if the type happens to be 16 bits wide?
>
> So type limit warnings break not things than they fix.

Yeah, too bad.

> These things come up in macros too (think range checking etc).
>
> In other words, that warning really isn't good if it's done mindlessly. And I've
> never seen a compiler that did it sanely and trying to take context into
> account.
>
> So no. Don't enable that broken warning. We have had it on, and it caused people
> to send in patches for warnings that made the code actively worse.

Okay. Please disregard my other mail.

Thanks,

Ingo


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