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    SubjectRe: [PATCH 01/14] x86, boot: align the .bss section in the decompressor
    On Thu, May 07, 2009 at 03:26:49PM -0700, H. Peter Anvin wrote:
    > From: H. Peter Anvin <hpa@zytor.com>
    >
    > Aligning the .bss section makes it trivially faster, and makes using
    > larger transfers for the clear slightly easier.
    >
    > [ Impact: trivial performance enhancement, future patch prep ]
    >
    > Signed-off-by: H. Peter Anvin <hpa@zytor.com>
    > ---
    > arch/x86/boot/compressed/vmlinux.lds.S | 1 +
    > 1 files changed, 1 insertions(+), 0 deletions(-)
    >
    > diff --git a/arch/x86/boot/compressed/vmlinux.lds.S b/arch/x86/boot/compressed/vmlinux.lds.S
    > index 0d26c92..27c168d 100644
    > --- a/arch/x86/boot/compressed/vmlinux.lds.S
    > +++ b/arch/x86/boot/compressed/vmlinux.lds.S
    > @@ -42,6 +42,7 @@ SECTIONS
    > *(.data.*)
    > _edata = . ;
    > }
    > + . = ALIGN(32);

    Where does this magic 32 comes from?
    I would assume the better choice would be:
    . = ALIGN(L1_CACHE_BYTES);

    So we match the relevant CPU.

    In general for alignmnet of output sections I see the need for:
    1) Function call
    2) L1_CACHE_BYTES
    3) PAGE_SIZE
    4) 2*PAGE_SIZE

    But I see magic constant used here and there that does not match
    the above (when looking at all archs).
    So I act when I see a new 'magic' number..

    Sam


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