diff mbox series

[03/15] ebpf-docs: Move Clang notes to a separate file

Message ID 20220927185958.14995-3-dthaler1968@googlemail.com (mailing list archive)
State Accepted
Commit 6c7aaffb24efbd5d1ae067b2b629b3ffcc37e18e
Delegated to: BPF
Headers show
Series [01/15] ebpf-docs: Move legacy packet instructions to a separate file | expand

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Commit Message

Dave Thaler Sept. 27, 2022, 6:59 p.m. UTC 
From: Dave Thaler <dthaler@microsoft.com>

Signed-off-by: Dave Thaler <dthaler@microsoft.com>
---
 Documentation/bpf/clang-notes.rst     | 24 ++++++++++++++++++++++++
 Documentation/bpf/instruction-set.rst |  6 ------
 2 files changed, 24 insertions(+), 6 deletions(-)
 create mode 100644 Documentation/bpf/clang-notes.rst
diff mbox series

Patch

diff --git a/Documentation/bpf/clang-notes.rst b/Documentation/bpf/clang-notes.rst
new file mode 100644
index 000000000..b15179cb5
--- /dev/null
+++ b/Documentation/bpf/clang-notes.rst
@@ -0,0 +1,24 @@ 
+.. contents::
+.. sectnum::
+
+==========================
+Clang implementation notes
+==========================
+
+This document provides more details specific to the Clang/LLVM implementation of the eBPF instruction set.
+
+Versions
+========
+
+Clang defined "CPU" versions, where a CPU version of 3 corresponds to the current eBPF ISA.
+
+Clang can select the eBPF ISA version using ``-mcpu=v3`` for example to select version 3.
+
+Atomic operations
+=================
+
+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``.
diff --git a/Documentation/bpf/instruction-set.rst b/Documentation/bpf/instruction-set.rst
index 1735b91ec..541483118 100644
--- a/Documentation/bpf/instruction-set.rst
+++ b/Documentation/bpf/instruction-set.rst
@@ -303,12 +303,6 @@  The ``BPF_CMPXCHG`` operation atomically compares the value addressed by
 value that was at ``dst_reg + off`` before the operation is zero-extended
 and loaded back to ``R0``.
 
-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``.
-
 64-bit immediate instructions
 -----------------------------