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    SubjectRe: [PATCH] [2/58] x86_64: Tell gcc to only align stack to 8 bytes
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    Andi Kleen <ak@suse.de> writes:

    > Don't need 16 byte alignment because kernel doesn't use SSE2
    >
    ...
    > cflags-y += -maccumulate-outgoing-args
    > +cflags-y += -mpreferred-stack-boundary=4
    >

    From gcc manpage:

    -mpreferred-stack-boundary=num
    Attempt to keep the stack boundary aligned to a 2 raised to num
    byte boundary. If -mpreferred-stack-boundary is not specified, the
    default is 4 (16 bytes or 128 bits), except when optimizing for
    code size (-Os), in which case the default is the minimum correct
    alignment (4 bytes for x86, and 8 bytes for x86-64).

    So -mpreferred-stack-boundary=4 is the default and to align stack
    to 8 bytes you want -mpreferred-stack-boundary=3, not 4, IIUC.
    -
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