| Message ID | 20210210142853.82203-1-iii@linux.ibm.com (mailing list archive) |
|---|---|
| State | Accepted |
| Delegated to: | BPF |
| Headers | show |
| Series | [bpf-next] docs: bpf: Clarify BPF_CMPXCHG wording | expand |
On Wed, Feb 10, 2021 at 6:29 AM Ilya Leoshkevich <iii@linux.ibm.com> wrote: > > 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> Applied.
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.
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> --- Documentation/networking/filter.rst | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)