On Mon, Nov 23, 2020 at 05:32:51PM -0800, Nick Desaulniers wrote:

On Sun, Nov 22, 2020 at 8:17 AM Kees Cook [off-list ref] wrote:

quoted

On Fri, Nov 20, 2020 at 11:51:42AM -0800, Jakub Kicinski wrote:

quoted

If none of the 140 patches here fix a real bug, and there is no change
to machine code then it sounds to me like a W=2 kind of a warning.

FWIW, this series has found at least one bug so far:
https://lore.kernel.org/lkml/CAFCwf11izHF=g1mGry1fE5kvFFFrxzhPSM6qKAO8gxSp=Kr_CQ@mail.gmail.com/ (local)

So looks like the bulk of these are:
switch (x) {
  case 0:
    ++x;
  default:
    break;
}

This should not generate a warning.

I have a patch that fixes those up for clang:
https://reviews.llvm.org/D91895

There's 3 other cases that don't quite match between GCC and Clang I
observe in the kernel:
switch (x) {
  case 0:
    ++x;
  default:
    goto y;
}
y:;

This should generate a warning.

switch (x) {
  case 0:
    ++x;
  default:
    return;
}

Warn for this.

switch (x) {
  case 0:
    ++x;
  default:
    ;
}

Don't warn for this.

If adding a break statement changes the flow of the code then warn about
potentially missing break statements, but if it doesn't change anything
then don't warn about it.

regards,
dan carpenter