[PATCH 11/13] powerpc64/bpf elfv2: Setup kernel TOC in r2 on entry

[Christophe Leroy]

Le 06/01/2022 à 12:45, Naveen N. Rao a écrit :
> In preparation for using kernel TOC, load the same in r2 on entry. With
> elfv1, the kernel TOC is already setup by our caller so we just emit a
> nop. We adjust the number of instructions to skip on a tail call
> accordingly.
> 
> Signed-off-by: Naveen N. Rao <naveen.n.rao at linux.vnet.ibm.com>
> ---
>   arch/powerpc/net/bpf_jit_comp64.c | 8 +++++++-
>   1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/powerpc/net/bpf_jit_comp64.c b/arch/powerpc/net/bpf_jit_comp64.c
> index ce4fc59bbd6a92..e05b577d95bf11 100644
> --- a/arch/powerpc/net/bpf_jit_comp64.c
> +++ b/arch/powerpc/net/bpf_jit_comp64.c
> @@ -73,6 +73,12 @@ void bpf_jit_build_prologue(u32 *image, struct codegen_context *ctx)
>   {
>   	int i;
>   
> +#ifdef PPC64_ELF_ABI_v2
> +	PPC_BPF_LL(_R2, _R13, offsetof(struct paca_struct, kernel_toc));
> +#else
> +	EMIT(PPC_RAW_NOP());
> +#endif

Can we avoid the #ifdef, using

	if (__is_defined(PPC64_ELF_ABI_v2))
		PPC_BPF_LL(_R2, _R13, offsetof(struct paca_struct, kernel_toc));
	else
		EMIT(PPC_RAW_NOP());

> +
>   	/*
>   	 * Initialize tail_call_cnt if we do tail calls.
>   	 * Otherwise, put in NOPs so that it can be skipped when we are
> @@ -87,7 +93,7 @@ void bpf_jit_build_prologue(u32 *image, struct codegen_context *ctx)
>   		EMIT(PPC_RAW_NOP());
>   	}
>   
> -#define BPF_TAILCALL_PROLOGUE_SIZE	8
> +#define BPF_TAILCALL_PROLOGUE_SIZE	12

Why not change that for v2 ABI only instead of adding a NOP ? ABI won't 
change during runtime AFAIU

>   
>   	if (bpf_has_stack_frame(ctx)) {
>   		/*