From mboxrd@z Thu Jan  1 00:00:00 1970
From: Jeremy Fitzhardinge <jeremy@goop.org>
Subject: Re: [RFC, PATCH 2/5] Paravirt_ops patch bugs.patch
Date: Thu, 19 Apr 2007 21:39:34 -0700
Message-ID: <46284406.2080007@goop.org>
References: <20070420015234.5D42EBFC@zach-dev2.vmware.com>
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To: Zachary Amsden <zach@vmware.com>
Cc: Andrew Morton <akpm@osdl.org>, Petr Vandrovec <petr@vmware.com>, Chaz Masden <zamsden@gmail.com>, Virtualization Mailing List <virtualization@lists.osdl.org>, Chris Wright <chrisw@sous-sol.org>, Andi Kleen <ak@muc.de>, Ingo Molnar <mingo@elte.hu>
List-Id: virtualization@lists.linuxfoundation.org

Zachary Amsden wrote:
> Failing to patch because not enough space is available for a call or jump
> or because the site clobbers do not allow the target clobbers to fit is
> a fatal error; it means the kernel can not be properly virtualized.
>   

No, that doesn't follow.  If the original site was:

patchable_start:
    push %eax
    push %ecx
    push %edx
    call *paravirt_ops + thingy
    pop
    pop
    pop
patchable_end:

then its perfectly OK to leave it as-is, even if the direct call's
destination clobbers are mismatched.  If the patcher wants to generate a
call to a C function in a context which can't deal with normal C calling
conventions, then it needs to also patch in appropriate save/restores.

    J