On Mon, 2018-03-19 at 14:11 -0700, H.J. Lu wrote: > vDSO code runs in userspace. Don't compile it with retpoline. > > Signed-off-by: H.J. Lu <hjl.to...@gmail.com>
There are cases where we might actually want userspace to be using retpoline though. We still only do IBPB for *some* processes, and haven't really even finished the argument about the heuristics we use for that. If this is only for the switch in __vdso_clock_gettime() then maybe we turn that into a series of if/else instead of a switch. Or just write it in asm. Or better still, teach GCC that when it's using retpoline, a jump table is *NOT* faster than a series of that many conditional branches. The costs are higher, and I don't think we taught GCC that yet, did we?
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