[bpf-next] bpf, docs: Move sentence about returning R0 to abi.rst

Commit Message

Dave Thaler May 17, 2024, 3:34 p.m. UTC

As discussed at LSF/MM/BPF, the sentence about using R0 for returning
values from calls is part of the calling convention and belongs in
abi.rst.  Any further additions or clarifications to this text are left
for future patches on abi.rst.  The current patch is simply to unblock
progression of instruction-set.rst to a standard.

In contrast, the restriction of register numbers to the range 0-10
is untouched, left in the instruction-set.rst definition of the
src_reg and dst_reg fields.

Signed-off-by: Dave Thaler <[e-mail]>
---
 Documentation/bpf/standardization/abi.rst             | 3 +++
 Documentation/bpf/standardization/instruction-set.rst | 3 ---
 2 files changed, 3 insertions(+), 3 deletions(-)

Comments

[e-mail] May 25, 2024, 5:50 p.m. UTC | #1

Hello:

This patch was applied to bpf/bpf-next.git (master)
by Alexei Starovoitov <[e-mail]>:

On Fri, 17 May 2024 08:34:45 -0700 you wrote:
> As discussed at LSF/MM/BPF, the sentence about using R0 for returning
> values from calls is part of the calling convention and belongs in
> abi.rst.  Any further additions or clarifications to this text are left
> for future patches on abi.rst.  The current patch is simply to unblock
> progression of instruction-set.rst to a standard.
> 
> In contrast, the restriction of register numbers to the range 0-10
> is untouched, left in the instruction-set.rst definition of the
> src_reg and dst_reg fields.
> 
> [...]

Here is the summary with links:
  - [bpf-next] bpf, docs: Move sentence about returning R0 to abi.rst
    https://git.kernel.org/bpf/bpf-next/c/4652072e7b9d

You are awesome, thank you!

Christoph Hellwig May 26, 2024, 9 a.m. UTC | #2

Looks good:

Reviewed-by: Christoph Hellwig <[e-mail]>

Shung-Hsi Yu May 27, 2024, 4:36 a.m. UTC | #3

On Fri, May 17, 2024 at 08:34:45AM GMT, Dave Thaler wrote:
> As discussed at LSF/MM/BPF, the sentence about using R0 for returning
> values from calls is part of the calling convention and belongs in
> abi.rst.  Any further additions or clarifications to this text are left
> for future patches on abi.rst.  The current patch is simply to unblock
> progression of instruction-set.rst to a standard.
> 
> In contrast, the restriction of register numbers to the range 0-10
> is untouched, left in the instruction-set.rst definition of the
> src_reg and dst_reg fields.
> 
> Signed-off-by: Dave Thaler <[e-mail]>

Acked-by: Shung-Hsi Yu <[e-mail]>

Patch

diff --git a/Documentation/bpf/standardization/abi.rst b/Documentation/bpf/standardization/abi.rst
index 0c2e10eeb..41514137c 100644
--- a/Documentation/bpf/standardization/abi.rst
+++ b/Documentation/bpf/standardization/abi.rst
@@ -23,3 +23,6 @@  The BPF calling convention is defined as:
 
 R0 - R5 are scratch registers and BPF programs needs to spill/fill them if
 necessary across calls.
+
+The BPF program needs to store the return value into register R0 before doing an
+``EXIT``.
diff --git a/Documentation/bpf/standardization/instruction-set.rst b/Documentation/bpf/standardization/instruction-set.rst
index 997560aba..c0d7d74e0 100644
--- a/Documentation/bpf/standardization/instruction-set.rst
+++ b/Documentation/bpf/standardization/instruction-set.rst
@@ -475,9 +475,6 @@  the jump instruction.  Thus 'PC += 1' skips execution of the next
 instruction if it's a basic instruction or results in undefined behavior
 if the next instruction is a 128-bit wide instruction.
 
-The BPF program needs to store the return value into register R0 before doing an
-``EXIT``.
-
 Example:
 
 ``{JSGE, X, JMP32}`` means::