Make clear the minimal kernel compile config for each ebpf functionalities

[rainkin1993]

Hi,

I usually see the question

everything is right (including kernel version, ebpf program, etc), but my ebpf programs still cannot work

Such kind of issues mostly caused by the kernel compile configurations.

However, bpf (at least now) does not provide a useful error message (yes, that's you load bpf program failed: Invalid argument) to indicate which kernel configuation is not enabled. Thus I try to make it clear and give a clear list of the minimal requirements of basic eBPF functionalities. Please correct me if I am wrong.

Index	Functionalities	Kernel Configuration	Describtion
1	Basic	CONFIG_BPF_SYSCALL	Enable the bpf() system call
2		CONFIG_BPF_JIT	BPF JIT support
3		CONFIG_HAVE_BPF_JIT	the dependency of CONFIG_BPF_JIT
4		CONFIG_HAVE_EBPF_JIT	the dependency of CONFIG_BPF_JIT
5		CONFIG_HAVE_CBPF_JIT	the dependency of CONFIG_BPF_JIT
6		CONFIG_MODULES	the dependency of CONFIG_BPF_JIT and CONFIG_KPROBES
7		CONFIG_BPF	Enable BPF VM
8		CONFIG_BPF_EVENTS	This allows the user to attach BPF programs to kprobe, uprobe, and tracepoint events.
9		CONFIG_PERF_EVENTS	the dependency of CONFIG_BPF_EVENTS and CONFIG_UPROBE_EVENTS
10		CONFIG_HAVE_PERF_EVENTS	the dependency of CONFIG_PERF_EVENTS
11		CONFIG_PROFILING	the dependency of CONFIG_PERF_EVENTS
12	CGroup	CONFIG_CGROUP_BPF	Allow attaching eBPF programs to a cgroup
13	Kprobes	CONFIG_KPROBE_EVENTS	Allow attaching to kprobes
14		CONFIG_KPROBES	the dependency of CONFIG_KPROBE_EVENTS
15		CONFIG_HAVE_KPROBES	the dependency of CONFIG_KPROBES
16		CONFIG_HAVE_REGS_AND_STACK_ACCESS_API	the dependency of CONFIG_KPROBE_EVENTS
17	Uprobes	CONFIG_UPROBE_EVENTS	Allow attaching to uprobes
18		CONFIG_ARCH_SUPPORTS_UPROBES	the dependency of CONFIG_UPROBE_EVENTS
19		CONFIG_UPROBES	the dependency of CONFIG_UPROBE_EVENTS
20		CONFIG_MMU	the dependency of CONFIG_UPROBE_EVENTS
21	Tracepoints	CONFIG_TRACEPOINTS	realted to Tracepoints
22		CONFIG_HAVE_SYSCALL_TRACEPOINTS	realted to Tracepoints
23	Raw Tracepoints	Same as Tracepoints

[yonghong-song]

This is a good idea. I think such information deserves a file like kernel_config.md under bcc/docs directory. Could you help with a pull request? For your information, kernel bpf selftests maintains a config file as well: linux:tools/testing/selftests/bpf/config, which contains some networking, security config as well. Thanks!

[rainkin1993]

Sure. I will take a look the selftest config file and polish the config table. If finished, I will send a PR.

[KentaTada]

@rainkin1993 We really need kernel_config.md to select only the settings we need. After your PR about the list of the minimal requirements is merged, we want to add items about additional functionalities like CONFIG_BPF_KPROBE_OVERRIDE. How is the progress on the PR?

[KentaTada]

I'm investigating and summarizing the recent configuration. [WIP] https://github.com/KentaTada/bcc/blob/add-kernel-config/docs/kernel_config.md

[KentaTada]

@chethanah

Thanks for the activity about https://github.com/iovisor/bcc/pull/4436

As of now, CONFIG_KPROBES_ON_FTRACE is not mandatory but for optimization. https://github.com/iovisor/bcc/pull/4436#discussion_r1073362452 Acutually, we don't use it because arm64 does not yet support it. So we may add the new functionalities kprobe optimization

When it comes to kprobe optimization, I forgot to consider kprobe muliti. In my understanding, kprobe multi depends on CONFIG_FPROBE.

Anyway, I'll increase items of kprobes when I have some time.