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    SubjectRe: [Xen-devel] [PATCH 8/9] xen/enlighten: Fix compile warnings.
    On Thu, 2011-09-29 at 20:52 +0100, Konrad Rzeszutek Wilk wrote:
    > linux/arch/x86/xen/enlighten.c: In function ‘xen_start_kernel’:
    > linux/arch/x86/xen/enlighten.c:226: warning: ‘cx’ may be used uninitialized in this function
    > linux/arch/x86/xen/enlighten.c:240: note: ‘cx’ was declared here

    Before 61f4237d5b005767a76f4f3694e68e6f78f392d9 we used to initialise cx
    to zero before calling xen_cpuid.

    947ccf9c3c30307b774af3666ee74fcd9f47f646 didn't put it back for some

    Regardless I'm not sure how cx can be unused while {a,b,d}x apparently
    are not. All four are passed to xen_cpuid(&ax, &bx, &cx, &dx) and even
    if gcc were being clever and looking into xen_cpuid all four are in the
    output constraints of the real cpuid asm call.

    Oh, I see, ax and cx are also in the input side of the asm and ax is
    initialised but cx is not and that is the use not the one later in

    I think that even if cpuid leaf ax=1 happens not to use the subleaf
    index in cx we'd be better to initialise cx=0 than use uninitialized_var


    > Signed-off-by: Konrad Rzeszutek Wilk <>
    > ---
    > arch/x86/xen/enlighten.c | 2 +-
    > 1 files changed, 1 insertions(+), 1 deletions(-)
    > diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
    > index 2d69617..9473861 100644
    > --- a/arch/x86/xen/enlighten.c
    > +++ b/arch/x86/xen/enlighten.c
    > @@ -237,7 +237,7 @@ static void xen_cpuid(unsigned int *ax, unsigned int *bx,
    > static void __init xen_init_cpuid_mask(void)
    > {
    > - unsigned int ax, bx, cx, dx;
    > + unsigned int ax, bx, uninitialized_var(cx), dx;
    > unsigned int xsave_mask;
    > cpuid_leaf1_edx_mask =

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