Re: [PATCH RFC bpf-next v1 2/4] bpf: Introduce load-acquire and store-release instructions

[Peilin Ye <yepeilin@google.com>]

On Fri, Dec 27, 2024 at 12:23:22AM +0000, Peilin Ye wrote:
>         if (off) {
> -               emit_a64_mov_i(true, tmp, off, ctx);
> -               emit(A64_ADD(true, tmp, tmp, ptr), ctx);
> -               ptr = tmp;
> +               if (is_addsub_imm(off)) {
> +                       emit(A64_ADD_I(true, ptr, ptr, off), ctx);
                                               ~~~

> +               } else if (is_addsub_imm(-off)) {
> +                       emit(A64_SUB_I(true, ptr, ptr, -off), ctx);
                                               ~~~

No, I must not write to the 'ptr' register here.

> +               } else {
> +                       emit_a64_mov_i(true, tmp, off, ctx);
> +                       emit(A64_ADD(true, tmp, tmp, ptr), ctx);
> +                       ptr = tmp;
> +               }
>         }

I will do this instead:

--- a/arch/arm64/net/bpf_jit_comp.c
+++ b/arch/arm64/net/bpf_jit_comp.c
@@ -658,8 +658,14 @@ static int emit_atomic_load_store(const struct bpf_insn *insn, struct jit_ctx *c
                ptr = dst;

        if (off) {
-               emit_a64_mov_i(true, tmp, off, ctx);
-               emit(A64_ADD(true, tmp, tmp, ptr), ctx);
+               if (is_addsub_imm(off)) {
+                       emit(A64_ADD_I(true, tmp, ptr, off), ctx);
+               } else if (is_addsub_imm(-off)) {
+                       emit(A64_SUB_I(true, tmp, ptr, -off), ctx);
+               } else {
+                       emit_a64_mov_i(true, tmp, off, ctx);
+                       emit(A64_ADD(true, tmp, tmp, ptr), ctx);
+               }
                ptr = tmp;
        }
        if (arena) {

Thanks,
Peilin Ye