From: Qian Cai <cai@lca.pw>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Hugh Dickins <hughd@google.com>,
"Darrick J. Wong" <darrick.wong@oracle.com>,
Andrew Morton <akpm@linux-foundation.org>,
Matej Kupljen <matej.kupljen@gmail.com>,
Al Viro <viro@zeniv.linux.org.uk>,
Dan Carpenter <dan.carpenter@oracle.com>,
Linux List Kernel Mailing <linux-kernel@vger.kernel.org>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
Linux-MM <linux-mm@kvack.org>
Subject: Re: [PATCH] tmpfs: fix uninitialized return value in shmem_link
Date: Wed, 27 Feb 2019 15:12:18 -0500 [thread overview]
Message-ID: <1551298338.7087.5.camel@lca.pw> (raw)
In-Reply-To: <1551276580.7087.1.camel@lca.pw>
On Wed, 2019-02-27 at 09:09 -0500, Qian Cai wrote:
> On Mon, 2019-02-25 at 16:07 -0800, Linus Torvalds wrote:
> > On Mon, Feb 25, 2019 at 4:03 PM Qian Cai <cai@lca.pw> wrote:
> > > >
> > > > Of course, that's just gcc. I have no idea what llvm ends up doing.
> > >
> > > Clang 7.0:
> > >
> > > # clang -O2 -S -Wall /tmp/test.c
> > > /tmp/test.c:46:6: warning: variable 'ret' is used uninitialized whenever
> > > 'if'
> > > condition is false [-Wsometimes-uninitialized]
> >
> > Ok, good.
> >
> > Do we have any clang builds in any of the zero-day robot
> > infrastructure or something? Should we?
> >
> > And maybe this was how Dan noticed the problem in the first place? Or
> > is it just because of his eagle-eyes?
> >
>
> BTW, even clang is able to generate warnings in your sample code, it does not
> generate any warnings when compiling the buggy shmem.o via "make CC=clang".
> Here is the objdump for arm64 (with KASAN_SW_TAGS inline).
>
Ah, thanks to the commit 6e8d666e9253 ("Disable "maybe-uninitialized" warning
globally"), it will no longer generate this type of warnings until using "make
W=1" due to the commit a76bcf557ef4 ("Kbuild: enable -Wmaybe-uninitialized
warning for 'make W=1'"). Anyway, the generated code is the same using clang
with and without this patch.
d_instantiate(dentry, inode);
4eec: 94000000 bl 0 <d_instantiate>
ret = shmem_reserve_inode(inode->i_sb);
4ef0: 2a1f03e0 mov w0, wzr <---- ret = 0
return ret;
next prev parent reply other threads:[~2019-02-27 20:12 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-02-21 22:21 [PATCH] tmpfs: fix uninitialized return value in shmem_link Darrick J. Wong
2019-02-21 23:05 ` Hugh Dickins
2019-02-23 6:35 ` Hugh Dickins
2019-02-25 19:53 ` Linus Torvalds
2019-02-25 20:34 ` Hugh Dickins
2019-02-25 22:34 ` Linus Torvalds
2019-02-25 23:58 ` Linus Torvalds
2019-02-26 0:03 ` Qian Cai
2019-02-26 0:07 ` Linus Torvalds
2019-02-26 0:29 ` Darrick J. Wong
2019-02-27 14:09 ` Qian Cai
2019-02-27 20:12 ` Qian Cai [this message]
2019-02-28 8:56 ` Nathan Chancellor
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