[PATCH bpf-next v2 1/2] docs: bpf: Fixup atomics markup

From: Brendan Jackman
Date: Mon Jan 18 2021 - 11:03:52 EST

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

NB this conflicts with Lukas' patch at [1], which just fixes the
warning. The scope of this one is a little broader.

[1] https://lore.kernel.org/bpf/CA+i-1C3cEXqxcXfD4sibQfx+dtmmzvOzruhk8J5pAw3g5v=KgA@xxxxxxxxxxxxxx/T/#t

Signed-off-by: Brendan Jackman <jackmanb@xxxxxxxxxx>
Documentation/networking/filter.rst | 19 ++++++++++---------
1 file changed, 10 insertions(+), 9 deletions(-)

diff --git a/Documentation/networking/filter.rst b/Documentation/networking/filter.rst
index f6d8f90e9a56..4c2bb4c6364d 100644
--- a/Documentation/networking/filter.rst
+++ b/Documentation/networking/filter.rst
@@ -1048,12 +1048,12 @@ Unlike classic BPF instruction set, eBPF has generic load/store operations::
Where size is one of: BPF_B or BPF_H or BPF_W or BPF_DW.

It also includes atomic operations, which use the immediate field for extra

.imm = BPF_ADD, .code = BPF_ATOMIC | BPF_W | BPF_STX: lock xadd *(u32 *)(dst_reg + off16) += src_reg
.imm = BPF_ADD, .code = BPF_ATOMIC | BPF_DW | BPF_STX: lock xadd *(u64 *)(dst_reg + off16) += src_reg

-The basic atomic operations supported are:
+The basic atomic operations supported are::

@@ -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::


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


@@ -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

-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