Re: [PATCH 01/17] kbuild: Disable -Waddress-of-packed-member for gcc 9

[Peter Zijlstra]

On Fri, Mar 22, 2019 at 02:58:51PM +0100, Arnd Bergmann wrote:
> On Thu, Mar 21, 2019 at 11:00 PM Andi Kleen <andi@xxxxxxxxxxxxxx> wrote:
> >
> > From: Andi Kleen <ak@xxxxxxxxxxxxxxx>
> >
> > This warning is very noisy in a default build with gcc 9.
> > Move it into W=2 only.
> >
> > Cc: arnd@xxxxxxxx
> > Cc: Masahiro Yamada <yamada.masahiro@xxxxxxxxxxxxx>
> > Signed-off-by: Andi Kleen <ak@xxxxxxxxxxxxxxx>
> 
> I think W=2 is too aggressive. On many architectures, this finds
> real bugs and the false positives tend to be trivial to fix
> (by removing the bogus __packed annotation), which improves
> the generated code in the process.
> 
> Moving it to W=1 for the moment is probably fine, but ideally
> I think we should fix the kernel to behave according to the
> C standard.

Lol... we're actively moving away from the C standard on many places.

Why does the silly compiler think it is a problem to take the address of
a member of a packed structure? That sounds like something that's
perfectly fine and useful.