[v1] soc: rockchip: power-domain: Fix clang warning about negative shift count
diff mbox

Message ID 20170311022153.139362-1-mka@chromium.org
State New
Headers show

Commit Message

Matthias Kaehlcke March 11, 2017, 2:21 a.m. UTC
The following warning is generated when building with clang:

drivers/soc/rockchip/pm_domains.c:726:22: error: shift count is negative [-Werror,-Wshift-count-negative]
        [RK3399_PD_TCPD0]       = DOMAIN_RK3399(8, 8, -1, false),
                                  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/soc/rockchip/pm_domains.c:101:2: note: expanded from macro 'DOMAIN_RK3399'
        DOMAIN(pwr, status, req, req, req, wakeup)
        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/soc/rockchip/pm_domains.c:88:27: note: expanded from macro 'DOMAIN'
        .req_mask = (req >= 0) ? BIT(req) : 0,          \
                                 ^~~~~~~~
include/linux/bitops.h:6:24: note: expanded from macro 'BIT'

The BIT macro is evaluated with the negative value -1, even though the
resulting value would not be assigned. To fix this we only pass values
between 0 and 63 to BIT(). Unfortunately this means that we lose the
benefit of the compiler checking for out of bounds errors.

Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
---
 drivers/soc/rockchip/pm_domains.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

Comments

Heiko Stuebner March 11, 2017, 12:03 p.m. UTC | #1
Hi Matthias,

Am Freitag, 10. März 2017, 18:21:53 CET schrieb Matthias Kaehlcke:
> The following warning is generated when building with clang:
> 
> drivers/soc/rockchip/pm_domains.c:726:22: error: shift count is negative
> [-Werror,-Wshift-count-negative] [RK3399_PD_TCPD0]       = DOMAIN_RK3399(8,
> 8, -1, false),
>                                   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> drivers/soc/rockchip/pm_domains.c:101:2: note: expanded from macro
> 'DOMAIN_RK3399' DOMAIN(pwr, status, req, req, req, wakeup)
>         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> drivers/soc/rockchip/pm_domains.c:88:27: note: expanded from macro 'DOMAIN'
>         .req_mask = (req >= 0) ? BIT(req) : 0,          \
>                                  ^~~~~~~~
> include/linux/bitops.h:6:24: note: expanded from macro 'BIT'
> 
> The BIT macro is evaluated with the negative value -1, even though the
> resulting value would not be assigned. To fix this we only pass values
> between 0 and 63 to BIT(). Unfortunately this means that we lose the
> benefit of the compiler checking for out of bounds errors.

I tend to disagree here. This looks more like a case of "fix your compiler".

That conditional seems perfectly valid as the BIT(req) will never be reached 
if req < 0 - your clang simply doesn't recognize the pattern somehow, while 
for example gcc does.

Catering to specific whims of specific compilers feels somehow wrong, as what 
will happen if some imaginary third compiler requires another different hack 
to be satisfied?


Heiko

> Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
> ---
>  drivers/soc/rockchip/pm_domains.c | 14 ++++++++------
>  1 file changed, 8 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/soc/rockchip/pm_domains.c
> b/drivers/soc/rockchip/pm_domains.c index 1c78c42416c6..6f2bb1222992 100644
> --- a/drivers/soc/rockchip/pm_domains.c
> +++ b/drivers/soc/rockchip/pm_domains.c
> @@ -77,13 +77,15 @@ struct rockchip_pmu {
> 
>  #define to_rockchip_pd(gpd) container_of(gpd, struct rockchip_pm_domain,
> genpd)
> 
> +#define RK_MASK(bit) ((bit >= 0) ? BIT(bit & 0x3f) : 0)
> +
>  #define DOMAIN(pwr, status, req, idle, ack, wakeup)	\
> -{						\
> -	.pwr_mask = (pwr >= 0) ? BIT(pwr) : 0,		\
> -	.status_mask = (status >= 0) ? BIT(status) : 0,	\
> -	.req_mask = (req >= 0) ? BIT(req) : 0,		\
> -	.idle_mask = (idle >= 0) ? BIT(idle) : 0,	\
> -	.ack_mask = (ack >= 0) ? BIT(ack) : 0,		\
> +{							\
> +	.pwr_mask = RK_MASK(pwr),			\
> +	.status_mask = RK_MASK(status),			\
> +	.req_mask = RK_MASK(req),			\
> +	.idle_mask = RK_MASK(idle),			\
> +	.ack_mask = RK_MASK(ack),			\
>  	.active_wakeup = wakeup,			\
>  }
Matthias Kaehlcke March 13, 2017, 5:22 p.m. UTC | #2
El Sat, Mar 11, 2017 at 01:03:48PM +0100 Heiko Stuebner ha dit:

> Hi Matthias,
> 
> Am Freitag, 10. März 2017, 18:21:53 CET schrieb Matthias Kaehlcke:
> > The following warning is generated when building with clang:
> > 
> > drivers/soc/rockchip/pm_domains.c:726:22: error: shift count is negative
> > [-Werror,-Wshift-count-negative] [RK3399_PD_TCPD0]       = DOMAIN_RK3399(8,
> > 8, -1, false),
> >                                   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > drivers/soc/rockchip/pm_domains.c:101:2: note: expanded from macro
> > 'DOMAIN_RK3399' DOMAIN(pwr, status, req, req, req, wakeup)
> >         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > drivers/soc/rockchip/pm_domains.c:88:27: note: expanded from macro 'DOMAIN'
> >         .req_mask = (req >= 0) ? BIT(req) : 0,          \
> >                                  ^~~~~~~~
> > include/linux/bitops.h:6:24: note: expanded from macro 'BIT'
> > 
> > The BIT macro is evaluated with the negative value -1, even though the
> > resulting value would not be assigned. To fix this we only pass values
> > between 0 and 63 to BIT(). Unfortunately this means that we lose the
> > benefit of the compiler checking for out of bounds errors.
> 
> I tend to disagree here. This looks more like a case of "fix your compiler".
> 
> That conditional seems perfectly valid as the BIT(req) will never be reached 
> if req < 0 - your clang simply doesn't recognize the pattern somehow, while 
> for example gcc does.

My interpretation is that with clang the '(req >= 0) ?' condition is
not evaluated by the preprocessor, but only by the compiler. This seems to
be different with gcc.

> Catering to specific whims of specific compilers feels somehow wrong, as what 
> will happen if some imaginary third compiler requires another different hack 
> to be satisfied?

I'll check with the clang developers if clang can be changed to behave
like gcc in this aspect.

Thanks

Matthias

> > Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
> > ---
> >  drivers/soc/rockchip/pm_domains.c | 14 ++++++++------
> >  1 file changed, 8 insertions(+), 6 deletions(-)
> > 
> > diff --git a/drivers/soc/rockchip/pm_domains.c
> > b/drivers/soc/rockchip/pm_domains.c index 1c78c42416c6..6f2bb1222992 100644
> > --- a/drivers/soc/rockchip/pm_domains.c
> > +++ b/drivers/soc/rockchip/pm_domains.c
> > @@ -77,13 +77,15 @@ struct rockchip_pmu {
> > 
> >  #define to_rockchip_pd(gpd) container_of(gpd, struct rockchip_pm_domain,
> > genpd)
> > 
> > +#define RK_MASK(bit) ((bit >= 0) ? BIT(bit & 0x3f) : 0)
> > +
> >  #define DOMAIN(pwr, status, req, idle, ack, wakeup)	\
> > -{						\
> > -	.pwr_mask = (pwr >= 0) ? BIT(pwr) : 0,		\
> > -	.status_mask = (status >= 0) ? BIT(status) : 0,	\
> > -	.req_mask = (req >= 0) ? BIT(req) : 0,		\
> > -	.idle_mask = (idle >= 0) ? BIT(idle) : 0,	\
> > -	.ack_mask = (ack >= 0) ? BIT(ack) : 0,		\
> > +{							\
> > +	.pwr_mask = RK_MASK(pwr),			\
> > +	.status_mask = RK_MASK(status),			\
> > +	.req_mask = RK_MASK(req),			\
> > +	.idle_mask = RK_MASK(idle),			\
> > +	.ack_mask = RK_MASK(ack),			\
> >  	.active_wakeup = wakeup,			\
> >  }
> 
>
Matthias Kaehlcke March 13, 2017, 6:49 p.m. UTC | #3
El Mon, Mar 13, 2017 at 10:22:22AM -0700 Matthias Kaehlcke ha dit:

> El Sat, Mar 11, 2017 at 01:03:48PM +0100 Heiko Stuebner ha dit:
> 
> > Hi Matthias,
> > 
> > Am Freitag, 10. März 2017, 18:21:53 CET schrieb Matthias Kaehlcke:
> > > The following warning is generated when building with clang:
> > > 
> > > drivers/soc/rockchip/pm_domains.c:726:22: error: shift count is negative
> > > [-Werror,-Wshift-count-negative] [RK3399_PD_TCPD0]       = DOMAIN_RK3399(8,
> > > 8, -1, false),
> > >                                   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > > drivers/soc/rockchip/pm_domains.c:101:2: note: expanded from macro
> > > 'DOMAIN_RK3399' DOMAIN(pwr, status, req, req, req, wakeup)
> > >         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > > drivers/soc/rockchip/pm_domains.c:88:27: note: expanded from macro 'DOMAIN'
> > >         .req_mask = (req >= 0) ? BIT(req) : 0,          \
> > >                                  ^~~~~~~~
> > > include/linux/bitops.h:6:24: note: expanded from macro 'BIT'
> > > 
> > > The BIT macro is evaluated with the negative value -1, even though the
> > > resulting value would not be assigned. To fix this we only pass values
> > > between 0 and 63 to BIT(). Unfortunately this means that we lose the
> > > benefit of the compiler checking for out of bounds errors.
> > 
> > I tend to disagree here. This looks more like a case of "fix your compiler".
> > 
> > That conditional seems perfectly valid as the BIT(req) will never be reached 
> > if req < 0 - your clang simply doesn't recognize the pattern somehow, while 
> > for example gcc does.
> 
> My interpretation is that with clang the '(req >= 0) ?' condition is
> not evaluated by the preprocessor, but only by the compiler. This seems to
> be different with gcc.
> 
> > Catering to specific whims of specific compilers feels somehow wrong, as what 
> > will happen if some imaginary third compiler requires another different hack 
> > to be satisfied?
> 
> I'll check with the clang developers if clang can be changed to behave
> like gcc in this aspect.

FYI:

"We currently don't construct control-flow graphs (CFGs) when
processing initializer expressions in a global context.  CFGs have
been used for doing a variety of flow-based warnings in functions, but
at this point they haven't been used for global initializer
expressions."

https://bugs.llvm.org//show_bug.cgi?id=10030

m.

Patch
diff mbox

diff --git a/drivers/soc/rockchip/pm_domains.c b/drivers/soc/rockchip/pm_domains.c
index 1c78c42416c6..6f2bb1222992 100644
--- a/drivers/soc/rockchip/pm_domains.c
+++ b/drivers/soc/rockchip/pm_domains.c
@@ -77,13 +77,15 @@  struct rockchip_pmu {
 
 #define to_rockchip_pd(gpd) container_of(gpd, struct rockchip_pm_domain, genpd)
 
+#define RK_MASK(bit) ((bit >= 0) ? BIT(bit & 0x3f) : 0)
+
 #define DOMAIN(pwr, status, req, idle, ack, wakeup)	\
-{						\
-	.pwr_mask = (pwr >= 0) ? BIT(pwr) : 0,		\
-	.status_mask = (status >= 0) ? BIT(status) : 0,	\
-	.req_mask = (req >= 0) ? BIT(req) : 0,		\
-	.idle_mask = (idle >= 0) ? BIT(idle) : 0,	\
-	.ack_mask = (ack >= 0) ? BIT(ack) : 0,		\
+{							\
+	.pwr_mask = RK_MASK(pwr),			\
+	.status_mask = RK_MASK(status),			\
+	.req_mask = RK_MASK(req),			\
+	.idle_mask = RK_MASK(idle),			\
+	.ack_mask = RK_MASK(ack),			\
 	.active_wakeup = wakeup,			\
 }