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Re: [RFC] Kernel livepatching support in GCC
- From: Andi Kleen <ak at linux dot intel dot com>
- To: David Brown <david dot brown at hesbynett dot no>
- Cc: Maxim Kuvyrkov <maxim dot kuvyrkov at linaro dot org>, GCC Development <gcc at gcc dot gnu dot org>, Li Bin <huawei dot libin at huawei dot com>, Takahiro Akashi <takahiro dot akashi at linaro dot org>
- Date: Thu, 4 Jun 2015 08:17:48 -0700
- Subject: Re: [RFC] Kernel livepatching support in GCC
- Authentication-results: sourceware.org; auth=none
- References: <844CBBAF-DA0E-4164-9E35-34075A26F665 at linaro dot org> <55701E26 dot 5050503 at hesbynett dot no>
> Rather than just a sequence of NOP's, should the first NOP be a
> unconditional branch to the beginning of the real function? I don't
> know if this applies to AArch64 cpus, but I believe some cpus can handle
> such branches already in the decode unit, thus avoiding any extra cycles
> for skipping the NOPs.
nops are very cheap. Typically they are already discard in the frontend.
It's unlikely all of this is worth it.
firstname.lastname@example.org -- Speaking for myself only