Messages in this thread | | | Subject | Re: [PATCH 09/31] x86/entry/32: Leave the kernel via trampoline stack | From | Denys Vlasenko <> | Date | Fri, 9 Feb 2018 18:17:07 +0100 |
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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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