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

[Christophe Leroy <christophe.leroy@csgroup.eu>]

Le 11/01/2022 à 15:35, Christophe Leroy a écrit :
> 
> 
> Le 11/01/2022 à 11:31, Naveen N. Rao a écrit :
>> Christophe Leroy wrote:
>>>
>>>
>>> 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@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());
>>
>> Hmm... that doesn't work for me. Is __is_defined() expected to work with
>> macros other than CONFIG options?
> 
> Yes, __is_defined() should work with any item.
> 
> It is IS_ENABLED() which is supposed to work only with CONFIG options.
> 
> See commit 5c189c523e78 ("powerpc/time: Fix mftb()/get_tb() for use with
> the compat VDSO")
> 
> Or commit ca5999fde0a1 ("mm: introduce include/linux/pgtable.h")

Ah ... wait.

It seems it expects a macro set to 1.

So it would require arch/powerpc/include/asm/types.h to be modified to 
define PPC64_ELF_ABI_v2 or PPC64_ELF_ABI_v1 as 1

Christophe