Messages in this thread |  | | | Date | Wed, 20 Jan 2010 20:58:26 +0100 | | From | Andi Kleen <> | | Subject | Re: [RFC] [PATCH 1/7] User Space Breakpoint Assistance Layer (UBP) |
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> Re: rewriting instructions that use rip-relative addressing. We do that > now. See handle_riprel_insn() in patch #2. (As far as we can tell, it > works, but we'd appreciate your review of it.)
Yes, but how do you get within 2GB of it? Add lots of holes in the address space?
> The instruction decoder is used only during instruction analysis, while > registering the probe -- i.e., in kernel space.
Registering the user probe? That means if there's a buffer overflow in there it would be exploitable.
> > > > In general the trend has been also to make traps faster in the CPU, make > > sure you're not optimizing for some old CPU here. > > I won't argue with that. What Avi seems to be proposing buys us a > speedup, but at the cost of increased complexity -- among other things, > splitting the instrumentation code between user space (in the "XOL" area > -- which would then be used for much more than XOL instruction slots)
You can't have a single XOL area, at least not if you want to support shared libraries on 64bit & rip relative.
> and kernel space. The splitting would presumably be handled by > higher-level code -- SystemTap, perf, or whatever. It's a neat idea, > but it seems like a v2 kind of feature.
I'm not sure it can even work, unless you severly limited the allowed instructions.
-Andi
-- ak@linux.intel.com -- Speaking for myself only.
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