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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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