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

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Date:	Fri, 11 Jul 2014 22:10:50 +0200
From:	Daniel Kiper <daniel.kiper@...cle.com>
To:	Boris Ostrovsky <boris.ostrovsky@...cle.com>
Cc:	linux-kernel@...r.kernel.org, x86@...nel.org,
	xen-devel@...ts.xenproject.org, 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 Fri, Jul 11, 2014 at 04:03:46PM -0400, Boris Ostrovsky wrote:
> 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.

Well, I thought about that a bit and I prefer function like Konrad.
Could you agree with him which solution do you (as maintainers) prefer?

Daniel
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