Learn EBPF Tracing: Tutorial and Examples | Hacker News Reader

Learn EBPF Tracing: Tutorial and Examples

brendangregg.com

147 pointsknoxa251120 comments

I want to try out eBPF tracing in Linux. I really do.

Last three times I tried to install bcc/bpftrace on my Debian boxes, I failed to do so. The situation has not changed for over a year. I'm not the only one:

https://github.com/iovisor/bcc/issues/678

https://github.com/iovisor/bcc/issues/1434

https://github.com/iovisor/bcc/issues/1985

I have ran ebpf on ubuntu, so not sure what the difference is with Debian. I will note that clang 3.7 is fairly old at this point, I have started building a more recent llvm+clang (7.0.0 stable) myself instead of relying on the installed package, then building bcc against that. You might try that route, although llvm takes an eternity to build.

> You might try that route, although llvm takes an eternity to build.

You don’t need to build it from source yourself. The LLVM people build and host packages for Debian and Ubuntu in package repos that anyone can install from.

Instructions here: https://apt.llvm.org/

Ah, true. I should note I build a statically linked llvm so I can deploy my project on different versions. The pre-built llvm should work for most people.

From the bpftrace tutorial, I would have expected the one-liner

    bpftrace -e 'tracepoint:syscalls:sys_enter_open { printf("%d %s\n", pid, str(args->filename)); }'

to show me all open calls as they happen. I would have expected to see an open when I cat a file, for example. But trying the one-liner, I only see a few opens of files in /proc.

Can anyone explain what's happening?

It actually turns out most of the calls are `openat(2)`. I had the same question initially.

(don't have access to a linux box I can test this on at the moment, so sorry for the stupid question)

In DTrace, you can specify a probe like

  syscall::*open*:entry / / { }

to grab open(2), openat(2), etc. Does eBPF allow wildcards in probe specifications?

You can do

    bpftrace -e 'tracepoint:syscalls:sys_enter_open* { printf("%d\n", pid); }'

but then you can't access the arguments of the different probes uniformly, i.e.

    bpftrace -e 'tracepoint:syscalls:sys_enter_open* { printf("%d %s\n", pid, str(args->filename)); }'

does not work.

You can do it like this:

    bpftrace -e 'tracepoint:syscalls:sys_enter_open { printf("%d %s\n", pid, str(args->filename)); } tracepoint:syscalls:sys_enter_openat { printf("%d %s\n", pid, str(args->filename)); }'

This is a bit awkward, but it seems that this will be fixed: https://github.com/iovisor/bpftrace/issues/132

There was this talk[0] at 35c3 introducing eBPF tracing. I still have it on my towatch list as I could not attend it.

[0] https://media.ccc.de/v/35c3-9532-kernel_tracing_with_ebpf

I use HTTPS Everywhere plugin for firefox... it's pretty surprising in 2019 how many network-related blogs and articles are on http links and the https equivalent is broken.

You can use Let's Encrypt, it's free. It makes me not want to listen to what's supposed to be their wisdom on networking matters if they can't even get that right.

Gregg isn’t a bad engineer. In fact, quite the opposite. Do yourself a favor and overlook the TLS on his read only blog.

Maybe he should do himself a favor and fix his broken :443, or disable it.

It's a performance blog not a networking blog. eBOF isn't limited to networking nor was this blog post.

... I said his https is broken. His https is broken.

Does that really need downvoting into oblivion?

That isn't all you said. The last line was unnecessary in making your point, and wasn't polite. That's why people are downvoting you.

His https is still broken.

Maybe he'll fix it if someone points it out to him.

You're going to miss out on something amazing, then.

HTTPS (and DNSSEC!) are antithetical to the idea of proper network engineering. Hierarchical, centralized control systems. Let's Encrypt being free should only make you more suspicious about who's making money from whom. No thank you.

Who is making money off let's encrypt? The service is provided for free.

Nothing is free.

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