* [PATCH bpf-next v4] bpf, docs: Explain helper functions
@ 2023-03-08 20:53 Dave Thaler
2023-03-10 21:10 ` patchwork-bot+netdevbpf
0 siblings, 1 reply; 2+ messages in thread
From: Dave Thaler @ 2023-03-08 20:53 UTC (permalink / raw)
To: bpf; +Cc: bpf, Dave Thaler
From: Dave Thaler <dthaler@microsoft.com>
Add brief text about existence of helper functions, with details to go in
separate psABI text.
Note that text about runtime functions (kfuncs) is part of a separate patch,
not this one.
Signed-off-by: Dave Thaler <dthaler@microsoft.com>
---
V1 -> V2: addressed comments from Alexei and Stanislav
V2 -> V3: addressed comments from David Vernet
V3 -> V4: removed text that should be in psABI
---
Documentation/bpf/clang-notes.rst | 6 ++++++
Documentation/bpf/instruction-set.rst | 9 ++++++++-
Documentation/bpf/linux-notes.rst | 8 ++++++++
3 files changed, 22 insertions(+), 1 deletion(-)
diff --git a/Documentation/bpf/clang-notes.rst b/Documentation/bpf/clang-notes.rst
index 528feddf2db..2c872a1ee08 100644
--- a/Documentation/bpf/clang-notes.rst
+++ b/Documentation/bpf/clang-notes.rst
@@ -20,6 +20,12 @@ Arithmetic instructions
For CPU versions prior to 3, Clang v7.0 and later can enable ``BPF_ALU`` support with
``-Xclang -target-feature -Xclang +alu32``. In CPU version 3, support is automatically included.
+Jump instructions
+=================
+
+If ``-O0`` is used, Clang will generate the ``BPF_CALL | BPF_X | BPF_JMP`` (0x8d)
+instruction, which is not supported by the Linux kernel verifier.
+
Atomic operations
=================
diff --git a/Documentation/bpf/instruction-set.rst b/Documentation/bpf/instruction-set.rst
index db8789e6969..5e43e14abe8 100644
--- a/Documentation/bpf/instruction-set.rst
+++ b/Documentation/bpf/instruction-set.rst
@@ -253,7 +253,7 @@ BPF_JSET 0x40 PC += off if dst & src
BPF_JNE 0x50 PC += off if dst != src
BPF_JSGT 0x60 PC += off if dst > src signed
BPF_JSGE 0x70 PC += off if dst >= src signed
-BPF_CALL 0x80 function call
+BPF_CALL 0x80 function call see `Helper functions`_
BPF_EXIT 0x90 function / program return BPF_JMP only
BPF_JLT 0xa0 PC += off if dst < src unsigned
BPF_JLE 0xb0 PC += off if dst <= src unsigned
@@ -264,6 +264,13 @@ BPF_JSLE 0xd0 PC += off if dst <= src signed
The eBPF program needs to store the return value into register R0 before doing a
BPF_EXIT.
+Helper functions
+~~~~~~~~~~~~~~~~
+
+Helper functions are a concept whereby BPF programs can call into a
+set of function calls exposed by the runtime. Each helper
+function is identified by an integer used in a ``BPF_CALL`` instruction.
+The available helper functions may differ for each program type.
Load and store instructions
===========================
diff --git a/Documentation/bpf/linux-notes.rst b/Documentation/bpf/linux-notes.rst
index 956b0c86699..f43b9c797bc 100644
--- a/Documentation/bpf/linux-notes.rst
+++ b/Documentation/bpf/linux-notes.rst
@@ -12,6 +12,14 @@ Byte swap instructions
``BPF_FROM_LE`` and ``BPF_FROM_BE`` exist as aliases for ``BPF_TO_LE`` and ``BPF_TO_BE`` respectively.
+Jump instructions
+=================
+
+``BPF_CALL | BPF_X | BPF_JMP`` (0x8d), where the helper function
+integer would be read from a specified register, is not currently supported
+by the verifier. Any programs with this instruction will fail to load
+until such support is added.
+
Legacy BPF Packet access instructions
=====================================
--
2.33.4
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH bpf-next v4] bpf, docs: Explain helper functions
2023-03-08 20:53 [PATCH bpf-next v4] bpf, docs: Explain helper functions Dave Thaler
@ 2023-03-10 21:10 ` patchwork-bot+netdevbpf
0 siblings, 0 replies; 2+ messages in thread
From: patchwork-bot+netdevbpf @ 2023-03-10 21:10 UTC (permalink / raw)
To: Dave Thaler; +Cc: bpf, bpf, dthaler
Hello:
This patch was applied to bpf/bpf-next.git (master)
by Alexei Starovoitov <ast@kernel.org>:
On Wed, 8 Mar 2023 20:53:03 +0000 you wrote:
> From: Dave Thaler <dthaler@microsoft.com>
>
> Add brief text about existence of helper functions, with details to go in
> separate psABI text.
>
> Note that text about runtime functions (kfuncs) is part of a separate patch,
> not this one.
>
> [...]
Here is the summary with links:
- [bpf-next,v4] bpf, docs: Explain helper functions
https://git.kernel.org/bpf/bpf-next/c/c1f9e14e3b67
You are awesome, thank you!
--
Deet-doot-dot, I am a bot.
https://korg.docs.kernel.org/patchwork/pwbot.html
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2023-03-08 20:53 [PATCH bpf-next v4] bpf, docs: Explain helper functions Dave Thaler
2023-03-10 21:10 ` patchwork-bot+netdevbpf
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