Commit 53fe5418 authored by Brendan Jackman's avatar Brendan Jackman Committed by Alexei Starovoitov
Browse files

docs: bpf: Fixup atomics markup 



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: default avatarBrendan Jackman <jackmanb@google.com>
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Reviewed-by: default avatarLukas Bulwahn <lukas.bulwahn@gmail.com>
Link: https://lore.kernel.org/bpf/20210120133946.2107897-2-jackmanb@google.com
parent 636d549f

Documentation/networking/filter.rst

+8 −7
Original line number Diff line number Diff line
@@ -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

value that was in memory before it was modified.



The more special operations are:

The more special operations are::



    BPF_XCHG



This atomically exchanges ``src_reg`` with the value addressed by ``dst_reg +

off``.

off``. ::



    BPF_CMPXCHG
@@ -1081,18 +1081,19 @@ before is loaded back to ``R0``. 


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

architecture v3 (``-mcpu=v3``). For older versions it can be enabled with

``-Xclang -target-feature -Xclang +alu32``.



You may encounter BPF_XADD - this is a legacy name for BPF_ATOMIC, referring to

the exclusive-add operation encoded when the immediate field is zero.

You may encounter ``BPF_XADD`` - this is a legacy name for ``BPF_ATOMIC``,

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

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.



eBPF verifier