From: Kees Cook <keescook@chromium.org>
To: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: "Jürgen Groß" <jgross@suse.com>,
xen-devel@lists.xenproject.org,
"Stefano Stabellini" <sstabellini@kernel.org>,
"Alexander Potapenko" <glider@google.com>,
linux-kernel@vger.kernel.org
Subject: Re: [Xen-devel] [PATCH] x86/xen: Distribute switch variables for initialization
Date: Thu, 20 Feb 2020 15:05:36 -0800 [thread overview]
Message-ID: <202002201505.C3863B2D0@keescook> (raw)
In-Reply-To: <8a7f5bd7-2bb6-d187-cc6e-87ff01c440ce@oracle.com>
On Thu, Feb 20, 2020 at 11:33:41AM -0500, Boris Ostrovsky wrote:
>
>
> On 2/20/20 1:37 AM, Jürgen Groß wrote:
> > On 20.02.20 07:23, 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.
> >>
> >> arch/x86/xen/enlighten_pv.c: In function ‘xen_write_msr_safe’:
> >> arch/x86/xen/enlighten_pv.c:904:12: warning: statement will never be
> >> executed [-Wswitch-unreachable]
> >> 904 | unsigned which;
> >> | ^~~~~
> >>
> >> [1] https://bugs.llvm.org/show_bug.cgi?id=44916
> >>
> >> Signed-off-by: Kees Cook <keescook@chromium.org>
> >
> > Reviewed-by: Juergen Gross <jgross@suse.com>
> >
>
> Applied to for-linus-5.6.
>
> (I replaced 'unsigned' with 'unsigned int' to quiet down checkpatch )
Oh, good call. Sorry I missed that!
Thanks!
--
Kees Cook
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Xen-devel@lists.xenproject.org
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WARNING: multiple messages have this Message-ID (diff)
From: Kees Cook <keescook@chromium.org>
To: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: "Jürgen Groß" <jgross@suse.com>,
"Alexander Potapenko" <glider@google.com>,
"Stefano Stabellini" <sstabellini@kernel.org>,
xen-devel@lists.xenproject.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] x86/xen: Distribute switch variables for initialization
Date: Thu, 20 Feb 2020 15:05:36 -0800 [thread overview]
Message-ID: <202002201505.C3863B2D0@keescook> (raw)
In-Reply-To: <8a7f5bd7-2bb6-d187-cc6e-87ff01c440ce@oracle.com>
On Thu, Feb 20, 2020 at 11:33:41AM -0500, Boris Ostrovsky wrote:
>
>
> On 2/20/20 1:37 AM, Jürgen Groß wrote:
> > On 20.02.20 07:23, 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.
> >>
> >> arch/x86/xen/enlighten_pv.c: In function ‘xen_write_msr_safe’:
> >> arch/x86/xen/enlighten_pv.c:904:12: warning: statement will never be
> >> executed [-Wswitch-unreachable]
> >> 904 | unsigned which;
> >> | ^~~~~
> >>
> >> [1] https://bugs.llvm.org/show_bug.cgi?id=44916
> >>
> >> Signed-off-by: Kees Cook <keescook@chromium.org>
> >
> > Reviewed-by: Juergen Gross <jgross@suse.com>
> >
>
> Applied to for-linus-5.6.
>
> (I replaced 'unsigned' with 'unsigned int' to quiet down checkpatch )
Oh, good call. Sorry I missed that!
Thanks!
--
Kees Cook
next prev parent reply other threads:[~2020-02-20 23:06 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-20 6:23 [Xen-devel] [PATCH] x86/xen: Distribute switch variables for initialization Kees Cook
2020-02-20 6:23 ` Kees Cook
2020-02-20 6:37 ` [Xen-devel] " Jürgen Groß
2020-02-20 6:37 ` Jürgen Groß
2020-02-20 16:33 ` [Xen-devel] " Boris Ostrovsky
2020-02-20 16:33 ` Boris Ostrovsky
2020-02-20 23:05 ` Kees Cook [this message]
2020-02-20 23:05 ` Kees Cook
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