Re: [PATCH] ppdev: Distribute switch variables for initialization

[Greg Kroah-Hartman]

On Mon, Feb 24, 2020 at 12:34:12PM +0000, Sudip Mukherjee wrote:
> On Wed, Feb 19, 2020 at 10:23:11PM -0800, Kees Cook wrote:
> > Variables declared in a switch statement before any case statements
> > cannot be automatically initialized with compiler instrumentation (as
> > they are not part of any execution flow). With GCC's proposed automatic
> > stack variable initialization feature, this triggers a warning (and they
> > don't get initialized). Clang's automatic stack variable initialization
> > (via CONFIG_INIT_STACK_ALL=y) doesn't throw a warning, but it also
> > doesn't initialize such variables[1]. Note that these warnings (or silent
> > skipping) happen before the dead-store elimination optimization phase,
> > so even when the automatic initializations are later elided in favor of
> > direct initializations, the warnings remain.
> > 
> > To avoid these problems, move such variables into the "case" where
> > they're used or lift them up into the main function body.
> > 
> > drivers/char/ppdev.c: In function âpp_do_ioctlâ:
> > drivers/char/ppdev.c:516:25: warning: statement will never be executed [-Wswitch-unreachable]
> >   516 |   struct ieee1284_info *info;
> >       |                         ^~~~
> > 
> > [1] https://bugs.llvm.org/show_bug.cgi?id=44916
> > 
> > Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
> 
> Acked-by: Sudip Mukherjee <sudipm.mukherjee@xxxxxxxxx>
> 
> Greg, Can you please take it in your tree...

Already taken :)