[PATCH] spi: rockchip: avoid objtool warning

[PATCH] spi: rockchip: avoid objtool warning

[Arnd Bergmann]

From: Arnd Bergmann <arnd@arndb.de>

Building this file with clang leads to a an unreachable code path
causing a warning from objtool:

drivers/spi/spi-rockchip.o: warning: objtool: rockchip_spi_transfer_one()+0x2e0: sibling call from callable instruction with modified stack frame

Use BUG() instead of unreachable() to avoid the undefined behavior
if it does happen.

Fixes: 65498c6ae241 ("spi: rockchip: support 4bit words")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
 drivers/spi/spi-rockchip.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/spi/spi-rockchip.c b/drivers/spi/spi-rockchip.c
index 936ef54e0903..972beac1169a 100644
--- a/drivers/spi/spi-rockchip.c
+++ b/drivers/spi/spi-rockchip.c
@@ -521,7 +521,7 @@ static void rockchip_spi_config(struct rockchip_spi *rs,
 		 * ctlr->bits_per_word_mask, so this shouldn't
 		 * happen
 		 */
-		unreachable();
+		BUG();
 	}
 
 	if (use_dma) {
-- 
2.29.2


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Re: [PATCH] spi: rockchip: avoid objtool warning

[Emil Renner Berthing]

On Thu, 25 Feb 2021 at 13:55, Arnd Bergmann <arnd@kernel.org> wrote:
>
> From: Arnd Bergmann <arnd@arndb.de>
>
> Building this file with clang leads to a an unreachable code path
> causing a warning from objtool:
>
> drivers/spi/spi-rockchip.o: warning: objtool: rockchip_spi_transfer_one()+0x2e0: sibling call from callable instruction with modified stack frame
>
> Use BUG() instead of unreachable() to avoid the undefined behavior
> if it does happen.
>
> Fixes: 65498c6ae241 ("spi: rockchip: support 4bit words")
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>

Acked-by: Emil Renner Berthing <kernel@esmil.dk>

> ---
>  drivers/spi/spi-rockchip.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/spi/spi-rockchip.c b/drivers/spi/spi-rockchip.c
> index 936ef54e0903..972beac1169a 100644
> --- a/drivers/spi/spi-rockchip.c
> +++ b/drivers/spi/spi-rockchip.c
> @@ -521,7 +521,7 @@ static void rockchip_spi_config(struct rockchip_spi *rs,
>                  * ctlr->bits_per_word_mask, so this shouldn't
>                  * happen
>                  */
> -               unreachable();
> +               BUG();
>         }
>
>         if (use_dma) {
> --
> 2.29.2
>

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Re: [PATCH] spi: rockchip: avoid objtool warning

[Nick Desaulniers]

On Thu, Feb 25, 2021 at 4:55 AM Arnd Bergmann <arnd@kernel.org> wrote:
>
> From: Arnd Bergmann <arnd@arndb.de>
>
> Building this file with clang leads to a an unreachable code path
> causing a warning from objtool:
>
> drivers/spi/spi-rockchip.o: warning: objtool: rockchip_spi_transfer_one()+0x2e0: sibling call from callable instruction with modified stack frame
>
> Use BUG() instead of unreachable() to avoid the undefined behavior
> if it does happen.

Thanks for the patch!

Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>

>
> Fixes: 65498c6ae241 ("spi: rockchip: support 4bit words")
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
>  drivers/spi/spi-rockchip.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/spi/spi-rockchip.c b/drivers/spi/spi-rockchip.c
> index 936ef54e0903..972beac1169a 100644
> --- a/drivers/spi/spi-rockchip.c
> +++ b/drivers/spi/spi-rockchip.c
> @@ -521,7 +521,7 @@ static void rockchip_spi_config(struct rockchip_spi *rs,
>                  * ctlr->bits_per_word_mask, so this shouldn't
>                  * happen
>                  */
> -               unreachable();
> +               BUG();
>         }
>
>         if (use_dma) {
> --
> 2.29.2
>


-- 
Thanks,
~Nick Desaulniers

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Re: [PATCH] spi: rockchip: avoid objtool warning

[Heiko Stübner]

Am Donnerstag, 25. Februar 2021, 13:55:34 CET schrieb Arnd Bergmann:
> From: Arnd Bergmann <arnd@arndb.de>
> 
> Building this file with clang leads to a an unreachable code path
> causing a warning from objtool:
> 
> drivers/spi/spi-rockchip.o: warning: objtool: rockchip_spi_transfer_one()+0x2e0: sibling call from callable instruction with modified stack frame
> 
> Use BUG() instead of unreachable() to avoid the undefined behavior
> if it does happen.
> 
> Fixes: 65498c6ae241 ("spi: rockchip: support 4bit words")
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>

Acked-by: Heiko Stuebner <heiko@sntech.de>

> ---
>  drivers/spi/spi-rockchip.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/spi/spi-rockchip.c b/drivers/spi/spi-rockchip.c
> index 936ef54e0903..972beac1169a 100644
> --- a/drivers/spi/spi-rockchip.c
> +++ b/drivers/spi/spi-rockchip.c
> @@ -521,7 +521,7 @@ static void rockchip_spi_config(struct rockchip_spi *rs,
>  		 * ctlr->bits_per_word_mask, so this shouldn't
>  		 * happen
>  		 */
> -		unreachable();
> +		BUG();
>  	}
>  
>  	if (use_dma) {
> 





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Re: [PATCH] spi: rockchip: avoid objtool warning

[Pratyush Yadav]

Hi,

On 25/02/21 01:55PM, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@arndb.de>
> 
> Building this file with clang leads to a an unreachable code path
> causing a warning from objtool:
> 
> drivers/spi/spi-rockchip.o: warning: objtool: rockchip_spi_transfer_one()+0x2e0: sibling call from callable instruction with modified stack frame
> 
> Use BUG() instead of unreachable() to avoid the undefined behavior
> if it does happen.
> 
> Fixes: 65498c6ae241 ("spi: rockchip: support 4bit words")
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
>  drivers/spi/spi-rockchip.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/spi/spi-rockchip.c b/drivers/spi/spi-rockchip.c
> index 936ef54e0903..972beac1169a 100644
> --- a/drivers/spi/spi-rockchip.c
> +++ b/drivers/spi/spi-rockchip.c
> @@ -521,7 +521,7 @@ static void rockchip_spi_config(struct rockchip_spi *rs,
>  		 * ctlr->bits_per_word_mask, so this shouldn't
>  		 * happen
>  		 */
> -		unreachable();
> +		BUG();

checkpatch says:

  Avoid crashing the kernel - try using WARN_ON & recovery code rather 
  than BUG() or BUG_ON()

Which makes sense to me. This is not something bad enough to justify 
crashing the kernel.

>  	}
>  
>  	if (use_dma) {
> -- 
> 2.29.2
> 

-- 
Regards,
Pratyush Yadav
Texas Instruments Inc.

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Re: [PATCH] spi: rockchip: avoid objtool warning

[Arnd Bergmann]

On Fri, Feb 26, 2021 at 9:16 AM 'Pratyush Yadav' via Clang Built Linux
<clang-built-linux@googlegroups.com> wrote:
>
> Hi,
>
> On 25/02/21 01:55PM, Arnd Bergmann wrote:
> > From: Arnd Bergmann <arnd@arndb.de>
> >
> > Building this file with clang leads to a an unreachable code path
> > causing a warning from objtool:
> >
> > drivers/spi/spi-rockchip.o: warning: objtool: rockchip_spi_transfer_one()+0x2e0: sibling call from callable instruction with modified stack frame
> >
> > Use BUG() instead of unreachable() to avoid the undefined behavior
> > if it does happen.
> >
> > Fixes: 65498c6ae241 ("spi: rockchip: support 4bit words")
> > Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> > ---
> >  drivers/spi/spi-rockchip.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/spi/spi-rockchip.c b/drivers/spi/spi-rockchip.c
> > index 936ef54e0903..972beac1169a 100644
> > --- a/drivers/spi/spi-rockchip.c
> > +++ b/drivers/spi/spi-rockchip.c
> > @@ -521,7 +521,7 @@ static void rockchip_spi_config(struct rockchip_spi *rs,
> >                * ctlr->bits_per_word_mask, so this shouldn't
> >                * happen
> >                */
> > -             unreachable();
> > +             BUG();
>
> checkpatch says:
>
>   Avoid crashing the kernel - try using WARN_ON & recovery code rather
>   than BUG() or BUG_ON()
>
> Which makes sense to me. This is not something bad enough to justify
> crashing the kernel.

I thought about rewriting it more thoroughly when I wrote the patch, but
couldn't come up with a good alternative, so I did the simplest change
in this direction, replacing the silent crash with a loud one.

Should we just dev_warn() and return instead, hoping that it won't do
more harm?

The backtrace from WARN_ON() probably doesn't help here.

       Arnd

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Re: [PATCH] spi: rockchip: avoid objtool warning

[Pratyush Yadav]

On 26/02/21 10:49AM, Arnd Bergmann wrote:
> On Fri, Feb 26, 2021 at 9:16 AM 'Pratyush Yadav' via Clang Built Linux
> <clang-built-linux@googlegroups.com> wrote:
> >
> > Hi,
> >
> > On 25/02/21 01:55PM, Arnd Bergmann wrote:
> > > From: Arnd Bergmann <arnd@arndb.de>
> > >
> > > Building this file with clang leads to a an unreachable code path
> > > causing a warning from objtool:
> > >
> > > drivers/spi/spi-rockchip.o: warning: objtool: rockchip_spi_transfer_one()+0x2e0: sibling call from callable instruction with modified stack frame
> > >
> > > Use BUG() instead of unreachable() to avoid the undefined behavior
> > > if it does happen.
> > >
> > > Fixes: 65498c6ae241 ("spi: rockchip: support 4bit words")
> > > Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> > > ---
> > >  drivers/spi/spi-rockchip.c | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/spi/spi-rockchip.c b/drivers/spi/spi-rockchip.c
> > > index 936ef54e0903..972beac1169a 100644
> > > --- a/drivers/spi/spi-rockchip.c
> > > +++ b/drivers/spi/spi-rockchip.c
> > > @@ -521,7 +521,7 @@ static void rockchip_spi_config(struct rockchip_spi *rs,
> > >                * ctlr->bits_per_word_mask, so this shouldn't
> > >                * happen
> > >                */
> > > -             unreachable();
> > > +             BUG();
> >
> > checkpatch says:
> >
> >   Avoid crashing the kernel - try using WARN_ON & recovery code rather
> >   than BUG() or BUG_ON()
> >
> > Which makes sense to me. This is not something bad enough to justify
> > crashing the kernel.
> 
> I thought about rewriting it more thoroughly when I wrote the patch, but
> couldn't come up with a good alternative, so I did the simplest change
> in this direction, replacing the silent crash with a loud one.
> 
> Should we just dev_warn() and return instead, hoping that it won't do
> more harm?

Hmm... I'm not very familiar with this device or driver so take what I 
say with a grain of salt. On the surface level it looks like it might 
end up doing something wrong or unexpected.

Returning an error code from this function (along with the dev_warn() or 
WARN_ON()) is the most sensible thing to do IMO. If the SPI layer sends 
an invalid value then the driver should be well within its rights to 
refuse the transaction. The function is currently void but making it 
return int seems fairly straightforward.

> 
> The backtrace from WARN_ON() probably doesn't help here.
> 
>        Arnd

-- 
Regards,
Pratyush Yadav
Texas Instruments Inc.

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Re: [PATCH] spi: rockchip: avoid objtool warning

[Arnd Bergmann]

On Fri, Feb 26, 2021 at 12:05 PM 'Pratyush Yadav' via Clang Built
Linux <clang-built-linux@googlegroups.com> wrote:
> On 26/02/21 10:49AM, Arnd Bergmann wrote:
> > On Fri, Feb 26, 2021 at 9:16 AM 'Pratyush Yadav' via Clang Built Linux <clang-built-linux@googlegroups.com> wrote:

>
> Returning an error code from this function (along with the dev_warn() or
> WARN_ON()) is the most sensible thing to do IMO. If the SPI layer sends
> an invalid value then the driver should be well within its rights to
> refuse the transaction. The function is currently void but making it
> return int seems fairly straightforward.

Indeed, this seems like a clear -EINVAL case. I've updated my patch, will
send after build testing.

       Arnd

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Re: [PATCH] spi: rockchip: avoid objtool warning

[Mark Brown]

On Thu, 25 Feb 2021 13:55:34 +0100, Arnd Bergmann wrote:
> Building this file with clang leads to a an unreachable code path
> causing a warning from objtool:
> 
> drivers/spi/spi-rockchip.o: warning: objtool: rockchip_spi_transfer_one()+0x2e0: sibling call from callable instruction with modified stack frame
> 
> Use BUG() instead of unreachable() to avoid the undefined behavior
> if it does happen.

Applied to

   https://git.kernel.org/pub/scm/linux/kernel/git/broonie/spi.git for-next

Thanks!

[1/1] spi: rockchip: avoid objtool warning
      commit: d86e880f7a7c5b64a650146a1353f98750863f21

All being well this means that it will be integrated into the linux-next
tree (usually sometime in the next 24 hours) and sent to Linus during
the next merge window (or sooner if it is a bug fix), however if
problems are discovered then the patch may be dropped or reverted.

You may get further e-mails resulting from automated or manual testing
and review of the tree, please engage with people reporting problems and
send followup patches addressing any issues that are reported if needed.

If any updates are required or you are submitting further changes they
should be sent as incremental updates against current git, existing
patches will not be replaced.

Please add any relevant lists and maintainers to the CCs when replying
to this mail.

Thanks,
Mark

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