[PATCH] ARM: fix unmet dependency on BITREVERSE for HAVE_ARCH_BITREVERSE

[PATCH] ARM: fix unmet dependency on BITREVERSE for HAVE_ARCH_BITREVERSE

[Julian Braha]

When ARM is enabled, and BITREVERSE is disabled,
Kbuild gives the following warning:

WARNING: unmet direct dependencies detected for HAVE_ARCH_BITREVERSE
  Depends on [n]: BITREVERSE [=n]
  Selected by [y]:
  - ARM [=y] && (CPU_32v7M [=n] || CPU_32v7 [=y]) && !CPU_32v6 [=n]

This is because ARM selects HAVE_ARCH_BITREVERSE
without selecting BITREVERSE, despite
HAVE_ARCH_BITREVERSE depending on BITREVERSE.

This unmet dependency bug was found by Kismet,
a static analysis tool for Kconfig. Please advise if this
is not the appropriate solution.

Signed-off-by: Julian Braha <julianbraha@gmail.com>
---
 arch/arm/Kconfig | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index f0f9e8bec83a..bf029623603e 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -67,6 +67,7 @@ config ARM
 	select GENERIC_SMP_IDLE_THREAD
 	select HARDIRQS_SW_RESEND
 	select HAVE_ARCH_AUDITSYSCALL if AEABI && !OABI_COMPAT
+	select BITREVERSE if (CPU_32v7M || CPU_32v7) && !CPU_32v6
 	select HAVE_ARCH_BITREVERSE if (CPU_32v7M || CPU_32v7) && !CPU_32v6
 	select HAVE_ARCH_JUMP_LABEL if !XIP_KERNEL && !CPU_ENDIAN_BE32 && MMU
 	select HAVE_ARCH_KGDB if !CPU_ENDIAN_BE32 && MMU
-- 
2.30.2


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Re: [PATCH] ARM: fix unmet dependency on BITREVERSE for HAVE_ARCH_BITREVERSE

[Arnd Bergmann]

On Fri, Oct 29, 2021 at 10:31 PM Julian Braha <julianbraha@gmail.com> wrote:
>
> When ARM is enabled, and BITREVERSE is disabled,
> Kbuild gives the following warning:
>
> WARNING: unmet direct dependencies detected for HAVE_ARCH_BITREVERSE
>   Depends on [n]: BITREVERSE [=n]
>   Selected by [y]:
>   - ARM [=y] && (CPU_32v7M [=n] || CPU_32v7 [=y]) && !CPU_32v6 [=n]
>
> This is because ARM selects HAVE_ARCH_BITREVERSE
> without selecting BITREVERSE, despite
> HAVE_ARCH_BITREVERSE depending on BITREVERSE.
>
> This unmet dependency bug was found by Kismet,
> a static analysis tool for Kconfig. Please advise if this
> is not the appropriate solution.
>
> Signed-off-by: Julian Braha <julianbraha@gmail.com>

This works, but I think it would be better handled differently:

The other 'select BITREVERSE' instances are for drivers that use
bitrever(), not those that provide it.

We can probably just remove the dependency. Alternatively we could
change arch/arm/ to

     select HAVE_ARCH_BITREVERSE if BITREVERSE && ((CPU_32v7M ||
CPU_32v7) && !CPU_32v6)

Regardless of what we do here, note that

a) the 'select' lines in CONFIG_ARM are sorted alphabetically, and
   should be kept that way

b) the same probably exists on arch/mips and arch/arm64, whatever we
   do here should be the same as on the other architectures.

        Arnd

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Re: [PATCH] ARM: fix unmet dependency on BITREVERSE for HAVE_ARCH_BITREVERSE

[Russell King (Oracle)]

On Sat, Oct 30, 2021 at 12:05:28AM +0200, Arnd Bergmann wrote:
> On Fri, Oct 29, 2021 at 10:31 PM Julian Braha <julianbraha@gmail.com> wrote:
> >
> > When ARM is enabled, and BITREVERSE is disabled,
> > Kbuild gives the following warning:
> >
> > WARNING: unmet direct dependencies detected for HAVE_ARCH_BITREVERSE
> >   Depends on [n]: BITREVERSE [=n]
> >   Selected by [y]:
> >   - ARM [=y] && (CPU_32v7M [=n] || CPU_32v7 [=y]) && !CPU_32v6 [=n]
> >
> > This is because ARM selects HAVE_ARCH_BITREVERSE
> > without selecting BITREVERSE, despite
> > HAVE_ARCH_BITREVERSE depending on BITREVERSE.
> >
> > This unmet dependency bug was found by Kismet,
> > a static analysis tool for Kconfig. Please advise if this
> > is not the appropriate solution.
> >
> > Signed-off-by: Julian Braha <julianbraha@gmail.com>
> 
> This works, but I think it would be better handled differently:
> 
> The other 'select BITREVERSE' instances are for drivers that use
> bitrever(), not those that provide it.
> 
> We can probably just remove the dependency. Alternatively we could
> change arch/arm/ to
> 
>      select HAVE_ARCH_BITREVERSE if BITREVERSE && ((CPU_32v7M ||
> CPU_32v7) && !CPU_32v6)
> 
> Regardless of what we do here, note that
> 
> a) the 'select' lines in CONFIG_ARM are sorted alphabetically, and
>    should be kept that way
> 
> b) the same probably exists on arch/mips and arch/arm64, whatever we
>    do here should be the same as on the other architectures.

I think HAVE_ARCH_BITREVERSE shouldn't depend on BITREVERSE.
BITREVERSE is set when something wants the bitreverse support.
HAVE_ARCH_BITREVERSE means that the architecture has support for
the bitreverse instructions and the generic code should not be
compiled.

I don't see any reason for HAVE_ARCH_BITREVERSE to depend on
BITREVERSE.

-- 
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