diff mbox series

[15/15] ebpf-docs: Add note about invalid instruction

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

Checks

Context Check Description
netdev/tree_selection success Not a local patch
bpf/vmtest-bpf-next-VM_Test-4 success Logs for llvm-toolchain
bpf/vmtest-bpf-next-VM_Test-5 success Logs for set-matrix
bpf/vmtest-bpf-next-VM_Test-2 success Logs for build for x86_64 with gcc
bpf/vmtest-bpf-next-VM_Test-3 success Logs for build for x86_64 with llvm-16
bpf/vmtest-bpf-next-VM_Test-1 success Logs for build for s390x with gcc
bpf/vmtest-bpf-next-VM_Test-16 success Logs for test_verifier on x86_64 with gcc
bpf/vmtest-bpf-next-VM_Test-13 success Logs for test_progs_no_alu32 on x86_64 with gcc
bpf/vmtest-bpf-next-VM_Test-15 success Logs for test_verifier on s390x with gcc
bpf/vmtest-bpf-next-VM_Test-17 success Logs for test_verifier on x86_64 with llvm-16
bpf/vmtest-bpf-next-VM_Test-7 success Logs for test_maps on x86_64 with gcc
bpf/vmtest-bpf-next-VM_Test-9 success Logs for test_progs on s390x with gcc
bpf/vmtest-bpf-next-VM_Test-10 success Logs for test_progs on x86_64 with gcc
bpf/vmtest-bpf-next-VM_Test-11 fail Logs for test_progs on x86_64 with llvm-16
bpf/vmtest-bpf-next-VM_Test-12 success Logs for test_progs_no_alu32 on s390x with gcc
bpf/vmtest-bpf-next-VM_Test-14 success Logs for test_progs_no_alu32 on x86_64 with llvm-16
bpf/vmtest-bpf-next-VM_Test-8 success Logs for test_maps on x86_64 with llvm-16
bpf/vmtest-bpf-next-PR fail PR summary
bpf/vmtest-bpf-next-VM_Test-6 success Logs for test_maps on s390x with gcc

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     | 5 +++++
 Documentation/bpf/instruction-set.rst | 3 +++
 2 files changed, 8 insertions(+)

Comments

Alexei Starovoitov Sept. 30, 2022, 10:21 p.m. UTC | #1 
On Tue, Sep 27, 2022 at 06:59:58PM +0000, dthaler1968@googlemail.com wrote:
> From: Dave Thaler <dthaler@microsoft.com>
> 
> Signed-off-by: Dave Thaler <dthaler@microsoft.com>
> ---
>  Documentation/bpf/clang-notes.rst     | 5 +++++
>  Documentation/bpf/instruction-set.rst | 3 +++
>  2 files changed, 8 insertions(+)
> 
> diff --git a/Documentation/bpf/clang-notes.rst b/Documentation/bpf/clang-notes.rst
> index 528feddf2..3c934421b 100644
> --- a/Documentation/bpf/clang-notes.rst
> +++ b/Documentation/bpf/clang-notes.rst
> @@ -20,6 +20,11 @@ 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.
>  
> +Invalid instructions
> +====================
> +
> +Clang will generate the invalid ``BPF_CALL | BPF_X | BPF_JMP`` (0x8d) instruction if ``-O0`` is used.

I wouldn't call it invalid and it's not related to -O0.
It's a "reserved" instruction.
When we support indirect jumps that's what it would be.

> +
>  Atomic operations
>  =================
>  
> diff --git a/Documentation/bpf/instruction-set.rst b/Documentation/bpf/instruction-set.rst
> index 2ac8f0dae..af9dc0cc6 100644
> --- a/Documentation/bpf/instruction-set.rst
> +++ b/Documentation/bpf/instruction-set.rst
> @@ -303,6 +303,9 @@ with the remaining registers being ignored.  The definition of a helper function
>  is responsible for specifying the type (e.g., integer, pointer, etc.) of the value returned,
>  the number of arguments, and the type of each argument.
>  
> +Note that ``BPF_CALL | BPF_X | BPF_JMP`` (0x8d), where the helper function integer
> +would be read from a specified register, is not currently permitted.

I would say:
Note that ``BPF_CALL | BPF_X | BPF_JMP`` instruction is reserved and currently not permitted.

> +
>  Runtime functions
>  ~~~~~~~~~~~~~~~~~
>  Runtime functions are like helper functions except that they are not specific
> -- 
> 2.33.4
>
diff mbox series

Patch

diff --git a/Documentation/bpf/clang-notes.rst b/Documentation/bpf/clang-notes.rst
index 528feddf2..3c934421b 100644
--- a/Documentation/bpf/clang-notes.rst
+++ b/Documentation/bpf/clang-notes.rst
@@ -20,6 +20,11 @@  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.
 
+Invalid instructions
+====================
+
+Clang will generate the invalid ``BPF_CALL | BPF_X | BPF_JMP`` (0x8d) instruction if ``-O0`` is used.
+
 Atomic operations
 =================
 
diff --git a/Documentation/bpf/instruction-set.rst b/Documentation/bpf/instruction-set.rst
index 2ac8f0dae..af9dc0cc6 100644
--- a/Documentation/bpf/instruction-set.rst
+++ b/Documentation/bpf/instruction-set.rst
@@ -303,6 +303,9 @@  with the remaining registers being ignored.  The definition of a helper function
 is responsible for specifying the type (e.g., integer, pointer, etc.) of the value returned,
 the number of arguments, and the type of each argument.
 
+Note that ``BPF_CALL | BPF_X | BPF_JMP`` (0x8d), where the helper function integer
+would be read from a specified register, is not currently permitted.
+
 Runtime functions
 ~~~~~~~~~~~~~~~~~
 Runtime functions are like helper functions except that they are not specific