Messages in this thread | | | From | Nadav Amit <> | Subject | Re: [PATCH v9 04/10] x86: refcount: prevent gcc distortions | Date | Thu, 4 Oct 2018 20:05:55 +0000 |
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at 12:33 PM, H. Peter Anvin <hpa@zytor.com> wrote:
> On 10/04/18 02:16, Ingo Molnar wrote: >> * hpa@zytor.com <hpa@zytor.com> wrote: >> >>> Ingo: I wasn't talking necessarily about the specifics of each bit, but rather the general >>> concept about being able to use macros in inlines... >> >> Ok, agreed about that part - and some of the patches did improve readability. >> >> Also, the 275 lines macros.s is a lot nicer than the 4,200 lines macros.S. >> >> Also, I'm not against using workarounds when the benefits are larger than the costs, but I am >> against *hiding* the fact that these are workarounds and that for some of them there are costs. > > Agreed, of course. > >>> I can send you something I have been working on in the background, but have been holding off >>> on because of this, in the morning my time. >> >> BTW., I have applied most of the series to tip:x86/kbuild already, and will push them out later >> today after some testing. I didn't apply the final 3 patches as they have dependencies, but >> applied the basics and fixed up the changelogs. >> >> So you can rely on this. > > Wonderful. > > Here is the horrible code I mentioned yesterday. This is about > implementing the immediate-patching framework that Linus and others have > discussed (it helps both performance and kernel hardening): > > Warning: this stuff can cause serious damage to your eyes, and this is a > just a small chunk of the whole mess; and relying on gas macros, as > brain damaged as they are, really is much, much cleaner than not: > > https://na01.safelinks.protection.outlook.com/?url=http:%2F%2Fwww.zytor.com%2F~hpa%2Ffoo.S&data=02%7C01%7Cnamit%40vmware.com%7C326f1a3beb4649df319508d62a3042fa%7Cb39138ca3cee4b4aa4d6cd83d9dd62f0%7C1%7C0%7C636742784111671122&sdata=anYIOXzlSTXPQKttTBHjSQgapBmaO9gfibBF34ZlHeQ%3D&reserved=0
Funny. Immediate-patching is what I was playing with when I encountered the gcc issue. Performance got worse instead of improving (or at least staying the same), because inlining got crazy.
Anyhow, wait for my soon-to-be-sent RFC in which I define a macro called “call” (to reduce the retpoline overhead) before you talk about damage to the eyes.
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