On 12/11/2015 12:05 AM, David Long wrote: > There is a moderate amount of code already in kprobes on ARM and the current > ARMv8 patch to deal with conditional execution of instructions. One aspect of > how this is handled is that instructions that fail their predicate and are > not (technically) executed are also not treated as a hit kprobe. Steve Capper > has suggested that the probe handling should still take place because we > stepped through the instruction even if it was effectively a nop. This would > be a significant change in how it currently works on 32-bit ARM, and a change > in the patch for ARMv8 (although it's not likely to be much of a change in > the kernel code). > > I need input on this. Do people have opinions? > > -dl >
Hi Dave, Conditionally executing the kprobes would violate the assumptions made for perf and systemtap collecting data. Even if the instruction is predicated and treated as a NOP it should still reliably trigger the kprobe. However, for efficiency the simulation/emulation/single-step of the instruction could be skipped if the instruction is known to have no change on the machine state other than changing the program counter. -Will Cohen -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
