Messages in this thread | | | Date | Sat, 12 Jul 2014 02:47:51 +0200 | From | Daniel Kiper <> | Subject | Re: [PATCH 2/2] arch/x86/xen: Silence compiler warnings |
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On Fri, Jul 11, 2014 at 08:14:51PM -0400, Konrad Rzeszutek Wilk wrote: > > On Jul 11, 2014 7:45 PM, Daniel Kiper <daniel.kiper@oracle.com> wrote: > > > > On Fri, Jul 11, 2014 at 04:32:27PM -0400, Boris Ostrovsky wrote: > > > On 07/11/2014 04:10 PM, Daniel Kiper wrote: > > > >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@oracle.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? > > > > > > > > > > I am not arguing against having a separate routine. All I am saying > > > is that calling xen_efi_init() when CONFIG_XEN_EFI is not defined > > > doesn't look logical. It will also add an unnecessary call (although > > > > Ahh... I misunderstood you. However, your proposal, as below: > > > > #ifdef CONFIG_XEN_EFI > > xen_efi_init(); > > #endif > > > > does not solve the problem because this vulnerable shift will be still > > visible for compiler during x86 32-bit kernel build. > > > > > compiler may optimize it out). > > > > Please loot at arch/x86/xen/enlighten.c:xen_check_mwait() and > > arch/x86/xen/enlighten.c:xen_boot_params_init_edd() (probably > > there are more stuff like that around). As I can see this is fairly > > common solution and probably compiler cope with it quite well. > > > > Those are some examples of some rather bad examples.
What is wrong with them?
> The way that is preferred in the Linux code is to have the ifdef in headers. > > See > http://lxr.free-electrons.com/source/arch/x86/include/asm/xen/swiotlb-xen.h > Or > http://lxr.free-electrons.com/source/arch/x86/include/asm/xen/pci.h > > You can create a similar file there and for the 32 bit implementation just make an empty static function. > > The 64 bit implementation has to be somewhere. Can it be in the Xen EFI file which is only compiled on 64 bit platforms?
OK, this (putting declaration/definition in *.h file) makes sens if you declare/define functions which must be called from different places. However, xen_efi_init() is called only once in arch/x86/xen/enlighten.c. Of course, I could define this function here in similar way like it is done in above headers but it take a bit more place. However, if you wish why not.
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