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SubjectRe: [PATCH 09/31] x86/entry/32: Leave the kernel via trampoline stack
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On 02/09/2018 06:05 PM, Linus Torvalds wrote:
> On Fri, Feb 9, 2018 at 1:25 AM, Joerg Roedel <joro@8bytes.org> wrote:
>> +
>> + /* Copy over the stack-frame */
>> + cld
>> + rep movsb
>
> Ugh. This is going to be horrendous. Maybe not noticeable on modern
> CPU's, but the whole 32-bit code is kind of pointless on a modern CPU.
>
> At least use "rep movsl". If the kernel stack isn't 4-byte aligned,
> you have issues.

Indeed, "rep movs" has some setup overhead that makes it undesirable
for small sizes. In my testing, moving less than 128 bytes with "rep movs"
is a loss.

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