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gerrit-public.fairphone.software / platform / external / bcc / 20fb64cd4ea76ecc6508ccdc7f3dc7a112082ea9
commit20fb64cd4ea76ecc6508ccdc7f3dc7a112082ea9[log] [tgz]
authorYonghong Song <yhs@fb.com>Sat Jun 02 00:28:38 2018 -0700
committerYonghong Song <yhs@fb.com>Sat Jun 02 16:28:40 2018 -0700
tree7e930995c1658327749dacad3f0aaa3ec6a27411
parentdb0933669aea6d85f4a1a4d04d5ad04dfbb55e71 [diff]
skip probe rewriter for bpf_probe_read()

bpf_probe_read() is often used to access pointees in bpf programs.
Recent rewriter has become smarter so a lot of bpf_probe_read()
can be replaced with simple pointer/member access.

In certain cases, bpf_probe_read() is still preferred though.
For example, kernel net/tcp.h defined TCP_SKB_CB as below
  #define TCP_SKB_CB(__skb)	((struct tcp_skb_cb *)&((__skb)->cb[0]))
User can use below to access tcp_gso_size of a skb data structure.
  TCP_SKB_CB(skb)->tcp_gso_size
The rewriter will fail as it attempts to rewrite (__skb)->cb[0].

Instead of chasing down to prevent exactly the above pattern,
this patch detects function bpf_probe_read() in ProbeVisitor and
will skip it so bpf_probe_read()'s third parameter is a AddrOf.
This can also help other cases where rewriter is not
capable and user used bpf_probe_read() as the workaround.

Also fixed tcptop.py to use direct assignment instead of
bpf_probe_read. Otherwise, rewriter will actually rewrite
src address reference inside the bpf_probe_read().

Signed-off-by: Yonghong Song <yhs@fb.com>
3 files changed
tree: 7e930995c1658327749dacad3f0aaa3ec6a27411
  1. cmake/
  2. debian/
  3. docs/
  4. examples/
  5. images/
  6. introspection/
  7. man/
  8. scripts/
  9. snapcraft/
  10. SPECS/
  11. src/
  12. tests/
  13. tools/
  14. .clang-format
  15. .dockerignore
  16. .gitignore
  17. .travis.yml
  18. CMakeLists.txt
  19. CODEOWNERS
  20. CONTRIBUTING-SCRIPTS.md
  21. COPYRIGHT.txt
  22. Dockerfile.debian
  23. Dockerfile.ubuntu
  24. FAQ.txt
  25. INSTALL.md
  26. LICENSE.txt
  27. LINKS.md
  28. QUICKSTART.md
  29. README.md
README.md

BCC Logo

BPF Compiler Collection (BCC)

BCC is a toolkit for creating efficient kernel tracing and manipulation programs, and includes several useful tools and examples. It makes use of extended BPF (Berkeley Packet Filters), formally known as eBPF, a new feature that was first added to Linux 3.15. Much of what BCC uses requires Linux 4.1 and above.

eBPF was described by Ingo Molnár as:

One of the more interesting features in this cycle is the ability to attach eBPF programs (user-defined, sandboxed bytecode executed by the kernel) to kprobes. This allows user-defined instrumentation on a live kernel image that can never crash, hang or interfere with the kernel negatively.

BCC makes BPF programs easier to write, with kernel instrumentation in C (and includes a C wrapper around LLVM), and front-ends in Python and lua. It is suited for many tasks, including performance analysis and network traffic control.

Screenshot

This example traces a disk I/O kernel function, and populates an in-kernel power-of-2 histogram of the I/O size. For efficiency, only the histogram summary is returned to user-level.

# ./bitehist.py
Tracing... Hit Ctrl-C to end.
^C
     kbytes          : count     distribution
       0 -> 1        : 3        |                                      |
       2 -> 3        : 0        |                                      |
       4 -> 7        : 211      |**********                            |
       8 -> 15       : 0        |                                      |
      16 -> 31       : 0        |                                      |
      32 -> 63       : 0        |                                      |
      64 -> 127      : 1        |                                      |
     128 -> 255      : 800      |**************************************|

The above output shows a bimodal distribution, where the largest mode of 800 I/O was between 128 and 255 Kbytes in size.

See the source: bitehist.py. What this traces, what this stores, and how the data is presented, can be entirely customized. This shows only some of many possible capabilities.

Installing

See INSTALL.md for installation steps on your platform.

FAQ

See FAQ.txt for the most common troubleshoot questions.

Reference guide

See docs/reference_guide.md for the reference guide to the bcc and bcc/BPF APIs.

Contents

Some of these are single files that contain both C and Python, others have a pair of .c and .py files, and some are directories of files.

Tracing

Examples:

Tools:

Networking

Examples:

BPF Introspection:

Tools that help to introspect BPF programs.

  • introspection/bps.c: List all BPF programs loaded into the kernel. 'ps' for BPF programs. Examples.

Motivation

BPF guarantees that the programs loaded into the kernel cannot crash, and cannot run forever, but yet BPF is general purpose enough to perform many arbitrary types of computation. Currently, it is possible to write a program in C that will compile into a valid BPF program, yet it is vastly easier to write a C program that will compile into invalid BPF (C is like that). The user won't know until trying to run the program whether it was valid or not.

With a BPF-specific frontend, one should be able to write in a language and receive feedback from the compiler on the validity as it pertains to a BPF backend. This toolkit aims to provide a frontend that can only create valid BPF programs while still harnessing its full flexibility.

Furthermore, current integrations with BPF have a kludgy workflow, sometimes involving compiling directly in a linux kernel source tree. This toolchain aims to minimize the time that a developer spends getting BPF compiled, and instead focus on the applications that can be written and the problems that can be solved with BPF.

The features of this toolkit include:

  • End-to-end BPF workflow in a shared library
    • A modified C language for BPF backends
    • Integration with llvm-bpf backend for JIT
    • Dynamic (un)loading of JITed programs
    • Support for BPF kernel hooks: socket filters, tc classifiers, tc actions, and kprobes
  • Bindings for Python
  • Examples for socket filters, tc classifiers, and kprobes
  • Self-contained tools for tracing a running system

In the future, more bindings besides python will likely be supported. Feel free to add support for the language of your choice and send a pull request!

Tutorials

Networking

At Red Hat Summit 2015, BCC was presented as part of a session on BPF. A multi-host vxlan environment is simulated and a BPF program used to monitor one of the physical interfaces. The BPF program keeps statistics on the inner and outer IP addresses traversing the interface, and the userspace component turns those statistics into a graph showing the traffic distribution at multiple granularities. See the code here.

Screenshot

Contributing

Already pumped up to commit some code? Here are some resources to join the discussions in the IOVisor community and see what you want to work on.

External links

Looking for more information on BCC and how it's being used? You can find links to other BCC content on the web in LINKS.md.