(2015/03/23 3:03), Alexei Starovoitov wrote: > On 3/22/15 3:06 AM, Masami Hiramatsu wrote: >> (2015/03/22 1:02), Alexei Starovoitov wrote: >>> On 3/21/15 5:14 AM, Masami Hiramatsu wrote: >>>> (2015/03/21 8:30), Alexei Starovoitov wrote: >>>>> >>>>> Note, kprobes are _not_ a stable kernel ABI, so bpf programs attached to >>>>> kprobes must be recompiled for every kernel version and user must supply correct >>>>> LINUX_VERSION_CODE in attr.kern_version during bpf_prog_load() call. >>>>> >>>> >>>> Would you mean that the ABI of kprobe-based BPF programs? Kprobe API/ABIs >>>> (register_kprobe() etc.) are stable, but the code who use kprobes certainly >>>> depends the kernel binary by design. So, if you meant it, BPF programs must >>>> be recompiled for every kernel binaries (including configuration changes, >>>> not only its version). >>> >>> yes. I mainly meant that bpf+kprobe programs must be recompiled >>> for every kernel binary. >> >> Hmm, if so, as we do in perf (and systemtap too), you'd better check >> kernel's build-id instead of the kernel version when loading the >> BPF program. It is safer than the KERNEL_VERSION_CODE. > > It's not about safety. As I mentioned in cover letter: > "version check is not used for safety, but for enforcing 'non-ABI-ness'" > In other words it's like check-box next to 'terms and conditions' > paragraph that the user has to click before he can continue. > By providing 'kern_version' during loading the user accepts the fact > that bpf+kprobe is not a stable ABI. Nothing more and nothing less. > build-id cannot achieve that, because it cannot be checked from inside > the kernel. Ah, I see. Hmm, I think we'd better have such interface (kernel API). > User space tools that will compile ktap/dtrace scripts into bpf might > use build-id for their own purpose, but that's a different discussion. Agreed. I'd like to discuss it since kprobe event interface may also have same issue. Thank you, -- Masami HIRAMATSU Software Platform Research Dept. Linux Technology Research Center Hitachi, Ltd., Yokohama Research Laboratory E-mail: masami.hiramatsu.pt@xxxxxxxxxxx -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
