Messages in this thread | | | Date | Fri, 3 Apr 2015 22:42:17 +0200 | From | Quentin Casasnovas <> | Subject | Re: [PATCH] x86/xsave: Robustify and merge macros |
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On Fri, Apr 03, 2015 at 07:48:24PM +0200, Borislav Petkov wrote: > On Fri, Apr 03, 2015 at 07:33:06PM +0200, Quentin Casasnovas wrote: > > > Basically, the idea was: > > > > > > .skip len(repl1) - len(orig), 0x90 > > > .skip len(repl2) - len(repl1), 0x90 > > > > > > BUT!, for some reason I changed it to what's there now and I can't > > > remember why anymore. > > > > I think it would not work in the case where repl1 is smaller or equal than > > orig_insn (i.e. no padding in the first .skip) but orig_insn is strictly > > smaller than repl2 (since we're never comparing repl2 with insn in this > > new-old code). > > orig_insn=4 > repl1=3 > repl2=5 > > .skip 0, 0x90 > .skip 2, 0x90 > > I think that still works, only the padding is larger than it needs to > be. And it is so many bytes larger as len(abs(repl1 - orig_insn)) is. > > In the example above, we'll get two bytes padding while only 1 suffices. >
Right.
> > Anything wrong with the two different approaches I've suggested in my > > original mail? > > Right now, I want to have a minimal fix for obvious reasons. We can > always improve stuff later when there's more time. >
If you're happy with the extra padding in such cases then your second approach looks okay to me. But IMO, even if taking the '.if' directive approach is certainly bigger LOC-wise, it should be much easier to review in a rush than some other .skip trickery.
It all depends on your definition of minimal change really, and whether that extra padding is acceptable or not for you :)
Quentin
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