diff mbox series

[bpf-next] bpf, docs: Clarify that MOVSX is only for BPF_X not BPF_K

Message ID 20240118232954.27206-1-dthaler1968@gmail.com (mailing list archive)
State Accepted
Commit 20e109ea9842158a153b24ef42ec5cc3d44e9485
Delegated to: BPF
Headers show
Series [bpf-next] bpf, docs: Clarify that MOVSX is only for BPF_X not BPF_K | expand

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Commit Message

Dave Thaler Jan. 18, 2024, 11:29 p.m. UTC 
Per discussion on the mailing list at
https://mailarchive.ietf.org/arch/msg/bpf/uQiqhURdtxV_ZQOTgjCdm-seh74/
the MOVSX operation is only defined to support register extension.

The document didn't previously state this and incorrectly implied
that one could use an immediate value.

Signed-off-by: Dave Thaler <dthaler1968@gmail.com>
---
 Documentation/bpf/standardization/instruction-set.rst | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

Comments

David Vernet Jan. 18, 2024, 11:45 p.m. UTC | #1 
On Thu, Jan 18, 2024 at 03:29:54PM -0800, Dave Thaler wrote:
> Per discussion on the mailing list at
> https://mailarchive.ietf.org/arch/msg/bpf/uQiqhURdtxV_ZQOTgjCdm-seh74/
> the MOVSX operation is only defined to support register extension.
> 
> The document didn't previously state this and incorrectly implied
> that one could use an immediate value.
> 
> Signed-off-by: Dave Thaler <dthaler1968@gmail.com>

Acked-by: David Vernet <void@manifault.com>
Yonghong Song Jan. 18, 2024, 11:53 p.m. UTC | #2 
On 1/18/24 3:29 PM, Dave Thaler wrote:
> Per discussion on the mailing list at
> https://mailarchive.ietf.org/arch/msg/bpf/uQiqhURdtxV_ZQOTgjCdm-seh74/
> the MOVSX operation is only defined to support register extension.
>
> The document didn't previously state this and incorrectly implied
> that one could use an immediate value.
>
> Signed-off-by: Dave Thaler <dthaler1968@gmail.com>

Acked-by: Yonghong Song <yonghong.song@linux.dev>
patchwork-bot+netdevbpf@kernel.org Jan. 23, 2024, 11:40 p.m. UTC | #3 
Hello:

This patch was applied to bpf/bpf-next.git (master)
by Alexei Starovoitov <ast@kernel.org>:

On Thu, 18 Jan 2024 15:29:54 -0800 you wrote:
> Per discussion on the mailing list at
> https://mailarchive.ietf.org/arch/msg/bpf/uQiqhURdtxV_ZQOTgjCdm-seh74/
> the MOVSX operation is only defined to support register extension.
> 
> The document didn't previously state this and incorrectly implied
> that one could use an immediate value.
> 
> [...]

Here is the summary with links:
  - [bpf-next] bpf, docs: Clarify that MOVSX is only for BPF_X not BPF_K
    https://git.kernel.org/bpf/bpf-next/c/20e109ea9842

You are awesome, thank you!
diff mbox series

Patch

diff --git a/Documentation/bpf/standardization/instruction-set.rst b/Documentation/bpf/standardization/instruction-set.rst
index eb0f234a8..d17a96c62 100644
--- a/Documentation/bpf/standardization/instruction-set.rst
+++ b/Documentation/bpf/standardization/instruction-set.rst
@@ -317,7 +317,8 @@  The ``BPF_MOVSX`` instruction does a move operation with sign extension.
 ``BPF_ALU | BPF_MOVSX`` :term:`sign extends<Sign Extend>` 8-bit and 16-bit operands into 32
 bit operands, and zeroes the remaining upper 32 bits.
 ``BPF_ALU64 | BPF_MOVSX`` :term:`sign extends<Sign Extend>` 8-bit, 16-bit, and 32-bit
-operands into 64 bit operands.
+operands into 64 bit operands.  Unlike other arithmetic instructions,
+``BPF_MOVSX`` is only defined for register source operands (``BPF_X``).
 
 Shift operations use a mask of 0x3F (63) for 64-bit operations and 0x1F (31)
 for 32-bit operations.