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docs: bpf: Fixup atomics markup

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This fixes up the markup to fix a warning, be more consistent with
use of monospace, and use the correct .rst syntax for <em> (* instead
of _).

Signed-off-by: Brendan Jackman <jackmanb@google.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Reviewed-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Link: https://lore.kernel.org/bpf/20210120133946.2107897-2-jackmanb@google.com
This commit is contained in:
Brendan Jackman 2021-01-20 13:39:45 +00:00 committed by Alexei Starovoitov
parent 636d549f91
commit 53fe5418fe
1 changed files with 8 additions and 7 deletions
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15
Documentation/networking/filter.rst
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@ -1066,12 +1066,12 @@ memory location addresed by ``dst_reg + off`` is atomically modified, with
immediate, then these operations also overwrite ``src_reg`` with the immediate, then these operations also overwrite ``src_reg`` with the
value that was in memory before it was modified. value that was in memory before it was modified.
The more special operations are: The more special operations are::
BPF_XCHG BPF_XCHG
This atomically exchanges ``src_reg`` with the value addressed by ``dst_reg + This atomically exchanges ``src_reg`` with the value addressed by ``dst_reg +
off``. off``. ::
BPF_CMPXCHG BPF_CMPXCHG
@ -1081,18 +1081,19 @@ before is loaded back to ``R0``.
Note that 1 and 2 byte atomic operations are not supported. Note that 1 and 2 byte atomic operations are not supported.
Except ``BPF_ADD`` _without_ ``BPF_FETCH`` (for legacy reasons), all 4 byte Except ``BPF_ADD`` *without* ``BPF_FETCH`` (for legacy reasons), all 4 byte
atomic operations require alu32 mode. Clang enables this mode by default in atomic operations require alu32 mode. Clang enables this mode by default in
architecture v3 (``-mcpu=v3``). For older versions it can be enabled with architecture v3 (``-mcpu=v3``). For older versions it can be enabled with
``-Xclang -target-feature -Xclang +alu32``. ``-Xclang -target-feature -Xclang +alu32``.
You may encounter BPF_XADD - this is a legacy name for BPF_ATOMIC, referring to You may encounter ``BPF_XADD`` - this is a legacy name for ``BPF_ATOMIC``,
the exclusive-add operation encoded when the immediate field is zero. referring to the exclusive-add operation encoded when the immediate field is
zero.
eBPF has one 16-byte instruction: BPF_LD | BPF_DW | BPF_IMM which consists eBPF has one 16-byte instruction: ``BPF_LD | BPF_DW | BPF_IMM`` which consists
of two consecutive ``struct bpf_insn`` 8-byte blocks and interpreted as single of two consecutive ``struct bpf_insn`` 8-byte blocks and interpreted as single
instruction that loads 64-bit immediate value into a dst_reg. instruction that loads 64-bit immediate value into a dst_reg.
Classic BPF has similar instruction: BPF_LD | BPF_W | BPF_IMM which loads Classic BPF has similar instruction: ``BPF_LD | BPF_W | BPF_IMM`` which loads
32-bit immediate value into a register. 32-bit immediate value into a register.
eBPF verifier eBPF verifier