From: Benjamin Block <bblock@linux.ibm.com>
To: Dan Carpenter <dan.carpenter@oracle.com>
Cc: Mailing List linux-smatch <smatch@vger.kernel.org>
Subject: Re: False Positive return_cast check
Date: Mon, 15 Feb 2021 17:04:09 +0100 [thread overview]
Message-ID: <YCqbeRbSdA4lCYR+@t480-pf1aa2c2.linux.ibm.com> (raw)
In-Reply-To: <20210215123625.GI2087@kadam>
On Mon, Feb 15, 2021 at 03:36:25PM +0300, Dan Carpenter wrote:
> On Fri, Feb 12, 2021 at 01:42:54PM +0100, Benjamin Block wrote:
> > Hello,
> >
> > I hope this is the right avenue to report this.
> >
> > I noticed yesterday that we get a false positive report from smatch for
> > `pathmask_to_pos()` in `arch/s390/include/asm/cio.h`. When reviewing
> > some code I got this error while using smatch:
Forgot to mention that I am using smatch at commit 1490b5d272bc
(heads/smatch-1.71).
> >
> > CHECK /home/bblock/src/linux/drivers/s390/cio/device_pgid.c
> > /home/bblock/src/linux/arch/s390/include/asm/cio.h:356 pathmask_to_pos() warn: signedness bug returning '(-119)'
> >
> > Which corresponds to this helper:
> >
> > static inline u8 pathmask_to_pos(u8 mask)
> > {
> > return 8 - ffs(mask);
> > }
> >
>
> Could you add some debug code, like this:
>
>
> #include "/path/to/smatch/check_debug.h"
> static inline u8 pathmask_to_pos(u8 mask)
> {
> __smatch_bits(mask);
> __smatch_implied(mask);
> __smatch_implied(ffs(mask));
> return 8 - ffs(mask);
> }
>
> Then run:
> /path/to/smatch/smatch_scripts/kchecker /home/bblock/src/linux/drivers/s390/cio/device_pgid.c
>
Sure,
I got this:
make[3]: Nothing to be done for 'drivers/s390/cio/device_pgid.o'.
CHECK /home/bblock/src/linux/drivers/s390/cio/device_pgid.c
/home/bblock/src/linux/arch/s390/include/asm/cio.h:358 pathmask_to_pos() bit info 'mask': definitely set 0x0. possibly set 0xff.
/home/bblock/src/linux/arch/s390/include/asm/cio.h:359 pathmask_to_pos() implied: mask = ''
/home/bblock/src/linux/arch/s390/include/asm/cio.h:360 pathmask_to_pos() implied: ffs(mask) = '0-127'
/home/bblock/src/linux/arch/s390/include/asm/cio.h:361 pathmask_to_pos() warn: signedness bug returning '(-119)'
(The long paths happen because I use out-of-tree builds with `O=/..`)
--
Best Regards, Benjamin Block / Linux on IBM Z Kernel Development / IBM Systems
IBM Deutschland Research & Development GmbH / https://www.ibm.com/privacy
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prev parent reply other threads:[~2021-02-15 16:05 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-12 12:42 False Positive return_cast check Benjamin Block
2021-02-15 12:36 ` Dan Carpenter
2021-02-15 16:04 ` Benjamin Block [this message]
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