Messages in this thread | | | Subject | Re: [Xen-devel] [PATCH 11/13] x86/paravirt: Add paravirt alternatives infrastructure | From | Boris Ostrovsky <> | Date | Tue, 17 Oct 2017 16:59:41 -0400 |
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On 10/17/2017 04:50 PM, Josh Poimboeuf wrote: > On Tue, Oct 17, 2017 at 04:36:00PM -0400, Boris Ostrovsky wrote: >> On 10/17/2017 04:17 PM, Josh Poimboeuf wrote: >>> On Tue, Oct 17, 2017 at 11:36:57AM -0400, Boris Ostrovsky wrote: >>>> On 10/17/2017 10:36 AM, Josh Poimboeuf wrote: >>>>> Maybe we can add a new field to the alternatives entry struct which >>>>> specifies the offset to the CALL instruction, so apply_alternatives() >>>>> can find it. >>>> We'd also have to assume that the restore part of an alternative entry >>>> is the same size as the save part. Which is true now. >>> Why? >>> >> Don't you need to know the size of the instruction without save and >> restore part? >> >> + if (a->replacementlen == 6 && *insnbuf == 0xff && *(insnbuf+1) == 0x15) >> >> Otherwise you'd need another field for the actual instruction length. > If we know where the CALL instruction starts, and can verify that it > starts with "ff 15", then we know the instruction length: 6 bytes. > Right? >
Oh, OK. Then you shouldn't need a->replacementlen test(s?) in apply_alternatives()?
-boris
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