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| author |   Ilya Leoshkevich <iii@linux.ibm.com> | 2021-02-10 15:28:52 +0100 |
|---|---|---|
| committer |   Alexei Starovoitov <ast@kernel.org> | 2021-02-11 22:01:13 -0800 |
| commit | 6a5df969ff80c1589ba9fd9136b77a4fb93371d0 (patch) | |
| tree | 8ac323eeaf198fc99730c65495799149aa85e880 | |
| parent | bpf: Clear per_cpu pointers during bpf_prog_realloc (diff) | |
| download | linux-dev-6a5df969ff80c1589ba9fd9136b77a4fb93371d0.tar.xz linux-dev-6a5df969ff80c1589ba9fd9136b77a4fb93371d0.zip | |
docs: bpf: Clarify BPF_CMPXCHG wording
Based on [1], BPF_CMPXCHG should always load the old value into R0. The
phrasing in bpf.rst is somewhat ambiguous in this regard, improve it to
make this aspect crystal clear.
[1] https://lore.kernel.org/bpf/CAADnVQJFcFwxEz=wnV=hkie-EDwa8s5JGbBQeFt1TGux1OihJw@mail.gmail.com/
Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20210210142853.82203-1-iii@linux.ibm.com
| -rw-r--r-- | Documentation/networking/filter.rst | 4 |
1 files changed, 2 insertions, 2 deletions
diff --git a/Documentation/networking/filter.rst b/Documentation/networking/filter.rst index b3f457802836..251c6bd73d15 100644 --- a/Documentation/networking/filter.rst +++ b/Documentation/networking/filter.rst @@ -1076,8 +1076,8 @@ off``. :: BPF_CMPXCHG This atomically compares the value addressed by ``dst_reg + off`` with -``R0``. If they match it is replaced with ``src_reg``, The value that was there -before is loaded back to ``R0``. +``R0``. If they match it is replaced with ``src_reg``. In either case, the +value that was there before is zero-extended and loaded back to ``R0``. Note that 1 and 2 byte atomic operations are not supported. |