linux-kernel - Re: [PATCH] xen: avoid type warning in xchg_xen

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Message-ID: <alpine.DEB.2.10.1705301636270.18759@sstabellini-ThinkPad-X260>
Date:   Tue, 30 May 2017 17:05:48 -0700 (PDT)
From:   Stefano Stabellini <sstabellini@...nel.org>
To:     Arnd Bergmann <arnd@...db.de>
cc:     Stefano Stabellini <sstabellini@...nel.org>,
        xen-devel@...ts.xenproject.org, Ian Abbott <abbotti@....co.uk>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] xen: avoid type warning in xchg_xen_ulong

On Mon, 29 May 2017, Arnd Bergmann wrote:
> The improved type-checking version of container_of() triggers a warning for
> xchg_xen_ulong, pointing out that 'xen_ulong_t' is unsigned, but atomic64_t
> contains a signed value:
> 
> drivers/xen/events/events_2l.c: In function 'evtchn_2l_handle_events':
> arch/x86/include/asm/cmpxchg.h:87:21: error: 'pending_words' is used uninitialized in this function [-Werror=uninitialized]

I don't think this is the warning message you wanted to paste here?
Other than that, the patch is fine.


> This adds a cast to work around the warning
> 
> Cc: Ian Abbott <abbotti@....co.uk>
> Fixes: 85323a991d40 ("xen: arm: mandate EABI and use generic atomic operations.")
> Fixes: daa2ac80834d ("kernel.h: handle pointers to arrays better in container_of()")
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
>  arch/arm/include/asm/xen/events.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/arm/include/asm/xen/events.h b/arch/arm/include/asm/xen/events.h
> index 71e473d05fcc..620dc75362e5 100644
> --- a/arch/arm/include/asm/xen/events.h
> +++ b/arch/arm/include/asm/xen/events.h
> @@ -16,7 +16,7 @@ static inline int xen_irqs_disabled(struct pt_regs *regs)
>  	return raw_irqs_disabled_flags(regs->ARM_cpsr);
>  }
>  
> -#define xchg_xen_ulong(ptr, val) atomic64_xchg(container_of((ptr),	\
> +#define xchg_xen_ulong(ptr, val) atomic64_xchg(container_of((long long*)(ptr),\
>  							    atomic64_t,	\
>  							    counter), (val))