Re: [PATCH v1 1/5] KVM: arm/arm64: Remove kvm_mmio_emulate tracepoint

[Zenghui Yu]

Hi James,

On 2019/6/12 20:48, James Morse wrote:
> Hi,
>
> On 12/06/2019 10:08, Zenghui Yu wrote:
> > In current KVM/ARM code, no one will invoke trace_kvm_mmio_emulate().
> > Remove this TRACE_EVENT definition.
>
> Oooer. We can't just go removing these things, they are visible to user-space.
>
> I recall an article on this: https://lwn.net/Articles/737530/
> "Another attempt to address the tracepoint ABI problem"
>
> I agree this is orphaned, it was added by commit 45e96ea6b369 ("KVM: ARM: Handle I/O
> aborts"), but there never was a caller.
>
> The problem with removing it is /sys/kernel/debug/tracing/events/kvm/kvm_mmio_emulate
> disappears. Any program relying on that being present (but useless) is now broken.
Thanks for the reminder.

It turned out that I knew little about the tracepoint ABI :( .
I'm OK to just drop this patch in next version.


Thanks,
zenghui


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