Difference from v2->v3 [1]:
* Just fixed a commite message, rebased, and added Lukas' review tag - thanks
Lukas!
Difference from v1->v2 [1]:
* Split into 2 patches
* Avoided unnecessary ': ::' in .rst source
* Tweaked wording of the -mcpu=v3 bit a little more
[1] Previous versions:
v1: https://lore.kernel.org/bpf/CA+i-1C1LVKjfQLBYk6siiqhxfy0jCR7UBcAmJ4jCED0A9aWsxA@mail.gmail.com/T/#t
v2: https://lore.kernel.org/bpf/[email protected]/T/#t
Brendan Jackman (2):
docs: bpf: Fixup atomics markup
docs: bpf: Clarify -mcpu=v3 requirement for atomic ops
Documentation/networking/filter.rst | 20 +++++++++++---------
1 file changed, 11 insertions(+), 9 deletions(-)
base-commit: 8edc0c67d09d6bf441eeb39ae9316fe07478093f
--
2.30.0.284.gd98b1dd5eaa7-goog
Alexei pointed out [1] that this wording is pretty confusing. Here's
an attempt to be more explicit and clear.
[1] https://lore.kernel.org/bpf/CAADnVQJVvwoZsE1K+6qRxzF7+6CvZNzygnoBW9tZNWJELk5c=Q@mail.gmail.com/T/#m07264fc18fdc43af02fc1320968afefcc73d96f4
Signed-off-by: Brendan Jackman <[email protected]>
---
Documentation/networking/filter.rst | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)
diff --git a/Documentation/networking/filter.rst b/Documentation/networking/filter.rst
index 4c2bb4c6364d..b3f457802836 100644
--- a/Documentation/networking/filter.rst
+++ b/Documentation/networking/filter.rst
@@ -1081,9 +1081,10 @@ 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
-atomic operations require alu32 mode. Clang enables this mode by default in
-architecture v3 (``-mcpu=v3``). For older versions it can be enabled with
+Clang can generate atomic instructions by default when ``-mcpu=v3`` is
+enabled. If a lower version for ``-mcpu`` is set, the only atomic instruction
+Clang can generate is ``BPF_ADD`` *without* ``BPF_FETCH``. If you need to enable
+the atomics features, while keeping a lower ``-mcpu`` version, you can use
``-Xclang -target-feature -Xclang +alu32``.
You may encounter ``BPF_XADD`` - this is a legacy name for ``BPF_ATOMIC``,
--
2.30.0.284.gd98b1dd5eaa7-goog
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 <[email protected]>
Reviewed-by: Lukas Bulwahn <[email protected]>
---
Documentation/networking/filter.rst | 15 ++++++++-------
1 file changed, 8 insertions(+), 7 deletions(-)
diff --git a/Documentation/networking/filter.rst b/Documentation/networking/filter.rst
index 45f6fde1776c..4c2bb4c6364d 100644
--- a/Documentation/networking/filter.rst
+++ b/Documentation/networking/filter.rst
@@ -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
--
2.30.0.284.gd98b1dd5eaa7-goog
On Wed, 20 Jan 2021 13:39:44 +0000
Brendan Jackman <[email protected]> wrote:
> Difference from v2->v3 [1]:
>
> * Just fixed a commite message, rebased, and added Lukas' review tag - thanks
> Lukas!
>
> Difference from v1->v2 [1]:
>
> * Split into 2 patches
>
> * Avoided unnecessary ': ::' in .rst source
>
> * Tweaked wording of the -mcpu=v3 bit a little more
>
> [1] Previous versions:
> v1: https://lore.kernel.org/bpf/CA+i-1C1LVKjfQLBYk6siiqhxfy0jCR7UBcAmJ4jCED0A9aWsxA@mail.gmail.com/T/#t
> v2: https://lore.kernel.org/bpf/[email protected]/T/#t
>
> Brendan Jackman (2):
> docs: bpf: Fixup atomics markup
> docs: bpf: Clarify -mcpu=v3 requirement for atomic ops
>
> Documentation/networking/filter.rst | 20 +++++++++++---------
> 1 file changed, 11 insertions(+), 9 deletions(-)
I'm assuming these will go up through the BPF/networking trees; please let
me know if I should pick them up instead.
Thanks,
jon
On Thu, Jan 21, 2021 at 10:54 AM Jonathan Corbet <[email protected]> wrote:
>
> On Wed, 20 Jan 2021 13:39:44 +0000
> Brendan Jackman <[email protected]> wrote:
>
> > Difference from v2->v3 [1]:
> >
> > * Just fixed a commite message, rebased, and added Lukas' review tag - thanks
> > Lukas!
> >
> > Difference from v1->v2 [1]:
> >
> > * Split into 2 patches
> >
> > * Avoided unnecessary ': ::' in .rst source
> >
> > * Tweaked wording of the -mcpu=v3 bit a little more
> >
> > [1] Previous versions:
> > v1: https://lore.kernel.org/bpf/CA+i-1C1LVKjfQLBYk6siiqhxfy0jCR7UBcAmJ4jCED0A9aWsxA@mail.gmail.com/T/#t
> > v2: https://lore.kernel.org/bpf/[email protected]/T/#t
> >
> > Brendan Jackman (2):
> > docs: bpf: Fixup atomics markup
> > docs: bpf: Clarify -mcpu=v3 requirement for atomic ops
> >
> > Documentation/networking/filter.rst | 20 +++++++++++---------
> > 1 file changed, 11 insertions(+), 9 deletions(-)
>
> I'm assuming these will go up through the BPF/networking trees; please let
> me know if I should pick them up instead.
I sent an email yesterday indicating that the set was applied to bpf-next.
There is no other tree it can be applied to without conflicts.
Looks like gmail is struggling again.