Re: [Intel-gfx] [PATCH 1/3] treewide: Lift switch variables out of switches

On Thu, Jan 24, 2019 at 4:44 AM Jani Nikula [off-list ref] wrote:

On Wed, 23 Jan 2019, Edwin Zimmerman [off-list ref] wrote:

quoted

On Wed, 23 Jan 2019, Jani Nikula [off-list ref] wrote:

quoted

On Wed, 23 Jan 2019, Greg KH [off-list ref] wrote:

quoted

On Wed, Jan 23, 2019 at 03:03:47AM -0800, Kees Cook wrote:

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Variables declared in a switch statement before any case statements
cannot be initialized, so move all instances out of the switches.
After this, future always-initialized stack variables will work
and not throw warnings like this:

fs/fcntl.c: In function ‘send_sigio_to_task’:
fs/fcntl.c:738:13: warning: statement will never be executed [-Wswitch-unreachable]
   siginfo_t si;
             ^~

That's a pain, so this means we can't have any new variables in { }
scope except for at the top of a function?

Just in case this wasn't clear: no, it's just the switch statement
before the first "case". I cannot imagine how bad it would be if we
couldn't have block-scoped variables! Heh. :)

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That's going to be a hard thing to keep from happening over time, as
this is valid C :(

Not all valid C is meant to be used! ;)

Very true.  The other thing to keep in mind is the burden of enforcing
a prohibition on a valid C construct like this.  It seems to me that
patch reviewers and maintainers have enough to do without forcing them
to watch for variable declarations in switch statements.  Automating
this prohibition, should it be accepted, seems like a good idea to me.

Considering that the treewide diffstat to fix this is:

 18 files changed, 45 insertions(+), 46 deletions(-)

and using the gcc plugin in question will trigger the switch-unreachable
warning, I think we're good. There'll probably be the occasional
declarations that pass through, and will get fixed afterwards.

Yeah, that was my thinking as well: it's a rare use, and we get a
warning when it comes up.

Thanks!

-- 
Kees Cook