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Date: Wed, 23 Jan 2019 13:09:13 +0100
From: Jann Horn <>
To: Greg KH <>
Cc: Kees Cook <>, kernel list <>, 
	Ard Biesheuvel <>, Laura Abbott <>, 
	Alexander Popov <>, xen-devel <>,,,, 
	Network Development <>,,, Linux-MM <>,,, 
	linux-security-module <>, 
	Kernel Hardening <>
Subject: Re: [PATCH 1/3] treewide: Lift switch variables out of switches

On Wed, Jan 23, 2019 at 1:04 PM Greg KH <> wrote:
> On Wed, Jan 23, 2019 at 03:03:47AM -0800, Kees Cook wrote:
> > 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?

AFAICS this only applies to switch statements (because they jump to a
case and don't execute stuff at the start of the block), not blocks
after if/while/... .

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

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