From: Dave Thaler <dthaler@xxxxxxxxxxxxx> Add note about reserved instruction Signed-off-by: Dave Thaler <dthaler@xxxxxxxxxxxxx> --- 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..40c618551 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. +Reserved instructions +==================== + +Clang will generate the reserved ``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 d0685a06f..72d59b3c6 100644 --- a/Documentation/bpf/instruction-set.rst +++ b/Documentation/bpf/instruction-set.rst @@ -301,6 +301,9 @@ 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 reserved and currently not permitted. + Runtime functions ~~~~~~~~~~~~~~~~~ Runtime functions are like helper functions except that they are not specific -- 2.33.4
