linux-kernel - Re: [PATCH v2] md/bcache: Mark _

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Message-ID: <202505080844.DD7F50F0A@keescook>
Date: Thu, 8 May 2025 08:58:48 -0700
From: Kees Cook <kees@...nel.org>
To: Coly Li <i@...y.li>
Cc: Coly Li <colyli@...nel.org>,
	Kent Overstreet <kent.overstreet@...ux.dev>,
	Ard Biesheuvel <ardb@...nel.org>, linux-bcache@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH v2] md/bcache: Mark __nonstring look-up table

On Thu, May 08, 2025 at 11:01:34AM +0800, Coly Li wrote:
> 
> > 2025年4月19日 11:55，Coly Li <i@...y.li> 写道：
> > 
> > 
> > 
> >> 2025年4月19日 04:21，Kees Cook <kees@...nel.org> 写道：
> >> 
> >> GCC 15's new -Wunterminated-string-initialization notices that the 16
> >> character lookup table "zero_uuid" (which is not used as a C-String)
> >> needs to be marked as "nonstring":
> >> 
> >> drivers/md/bcache/super.c: In function 'uuid_find_empty':
> >> drivers/md/bcache/super.c:549:43: warning: initializer-string for array of 'char' truncates NUL terminator but destination lacks 'nonstring' attribute (17 chars into 16 available) [-Wunterminated-string-initialization]
> >> 549 |         static const char zero_uuid[16] = "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0";
> >>     |                                           ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> >> 
> >> Add the annotation (since it is not used as a C-String), and switch the
> >> initializer to an array of bytes.
> >> 
> >> Signed-off-by: Kees Cook <kees@...nel.org>
> >> ---
> >> v2: use byte array initializer (colyli)
> >> v1: https://lore.kernel.org/all/20250416220135.work.394-kees@kernel.org/
> >> Cc: Coly Li <colyli@...nel.org>
> >> Cc: Kent Overstreet <kent.overstreet@...ux.dev>
> >> Cc: Ard Biesheuvel <ardb@...nel.org>
> >> Cc: linux-bcache@...r.kernel.org
> >> ---
> >> drivers/md/bcache/super.c | 3 ++-
> >> 1 file changed, 2 insertions(+), 1 deletion(-)
> >> 
> >> diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
> >> index e42f1400cea9..a76ce92502ed 100644
> >> --- a/drivers/md/bcache/super.c
> >> +++ b/drivers/md/bcache/super.c
> >> @@ -546,7 +546,8 @@ static struct uuid_entry *uuid_find(struct cache_set *c, const char *uuid)
> >> 
> >> static struct uuid_entry *uuid_find_empty(struct cache_set *c)
> >> {
> >> - static const char zero_uuid[16] = "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0";
> >> + static const char zero_uuid[] __nonstring =
> > 
> 
> Hi Kees,
> 
> > I notice zero_uuid[16] changes to zero_uuid[], then the element number information is removed.
> > 
> > Is it OK for GCC 15 to only add __nonstring and keep zero_uuid[16]?

Either way is fine. I can update the patch to use the "[16]" again if
you'd like?

-Kees

> Ping ?
> 
> You are expert here, I need your opinion.
> 
> Thanks.
> 
> Coly Li
> 
> 
> 
> >> + { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 };
> >> 
> >> return uuid_find(c, zero_uuid);
> >> }
> >> -- 
> >> 2.34.1
> 
> 

-- 
Kees Cook