linux-kernel - Re: [PATCH 2/2] arch/x86/xen: Silence compiler warnings

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Date:	Fri, 11 Jul 2014 16:03:46 -0400
From:	Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:	Daniel Kiper <daniel.kiper@...cle.com>,
	linux-kernel@...r.kernel.org, x86@...nel.org,
	xen-devel@...ts.xenproject.org
CC:	andrew.cooper3@...rix.com, david.vrabel@...rix.com, hpa@...or.com,
	ian.campbell@...rix.com, jbeulich@...e.com, jeremy@...p.org,
	konrad.wilk@...cle.com, matt.fleming@...el.com, mingo@...hat.com,
	stefano.stabellini@...citrix.com, tglx@...utronix.de
Subject: Re: [PATCH 2/2] arch/x86/xen: Silence compiler warnings

On 07/11/2014 03:54 PM, Daniel Kiper wrote:
> Compiler complains in the following way when x86 32-bit kernel
> with Xen support is build:
>
>    CC      arch/x86/xen/enlighten.o
> arch/x86/xen/enlighten.c: In function ‘xen_start_kernel’:
> arch/x86/xen/enlighten.c:1726:3: warning: right shift count >= width of type [enabled by default]
>
> Such line contains following EFI initialization code:
>
> boot_params.efi_info.efi_systab_hi = (__u32)(__pa(efi_systab_xen) >> 32);
>
> There is no issue if x86 64-bit kernel is build. However, 32-bit case
> generate warning (even if that code will not be executed because Xen
> does not work on 32-bit EFI platforms) due to __pa() returning unsigned long
> type which has 32-bits width. So move whole EFI initialization stuff
> to separate function and build its body conditionally to avoid above
> mentioned warning on x86 32-bit architecture.
>
> Signed-off-by: Daniel Kiper <daniel.kiper@...cle.com>
> ---
>   arch/x86/xen/enlighten.c |   35 ++++++++++++++++++++++-------------
>   1 file changed, 22 insertions(+), 13 deletions(-)
>
> diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
> index bc89647..6abec74 100644
> --- a/arch/x86/xen/enlighten.c
> +++ b/arch/x86/xen/enlighten.c
> @@ -1516,12 +1516,32 @@ static void __init xen_pvh_early_guest_init(void)
>   #endif
>   }
>   
> +static void __init xen_efi_init(void)
> +{
> +#ifdef CONFIG_XEN_EFI
> +	efi_system_table_t *efi_systab_xen;
> +
> +	efi_systab_xen = xen_efi_probe();
> +
> +	if (efi_systab_xen == NULL)
> +		return;
> +
> +	strncpy((char *)&boot_params.efi_info.efi_loader_signature, "Xen",
> +			sizeof(boot_params.efi_info.efi_loader_signature));
> +	boot_params.efi_info.efi_systab = (__u32)__pa(efi_systab_xen);
> +	boot_params.efi_info.efi_systab_hi = (__u32)(__pa(efi_systab_xen) >> 32);
> +
> +	set_bit(EFI_BOOT, &efi.flags);
> +	set_bit(EFI_PARAVIRT, &efi.flags);
> +	set_bit(EFI_64BIT, &efi.flags);
> +#endif
> +}
> +
>   /* First C function to be called on Xen boot */
>   asmlinkage __visible void __init xen_start_kernel(void)
>   {
>   	struct physdev_set_iopl set_iopl;
>   	int rc;
> -	efi_system_table_t *efi_systab_xen;
>   
>   	if (!xen_start_info)
>   		return;
> @@ -1717,18 +1737,7 @@ asmlinkage __visible void __init xen_start_kernel(void)
>   
>   	xen_setup_runstate_info(0);
>   
> -	efi_systab_xen = xen_efi_probe();
> -
> -	if (efi_systab_xen) {
> -		strncpy((char *)&boot_params.efi_info.efi_loader_signature, "Xen",
> -				sizeof(boot_params.efi_info.efi_loader_signature));
> -		boot_params.efi_info.efi_systab = (__u32)__pa(efi_systab_xen);
> -		boot_params.efi_info.efi_systab_hi = (__u32)(__pa(efi_systab_xen) >> 32);
> -
> -		set_bit(EFI_BOOT, &efi.flags);
> -		set_bit(EFI_PARAVIRT, &efi.flags);
> -		set_bit(EFI_64BIT, &efi.flags);
> -	}
> +	xen_efi_init();

I'd put ifdef CONFIG_XEN_EFI around the call instead of having it inside 
the routine.

-boris

>   
>   	/* Start the world */
>   #ifdef CONFIG_X86_32

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