linux-kernel - Re: [PATCH bpf-next v3 4/6] libbpf: Unify memory address casting operation style

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Date:   Sat, 9 Jul 2022 09:32:37 +0800
From:   Pu Lehui <pulehui@...wei.com>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>
CC:     Daniel Borkmann <daniel@...earbox.net>, bpf <bpf@...r.kernel.org>,
        <linux-riscv@...ts.infradead.org>,
        Networking <netdev@...r.kernel.org>,
        "open list" <linux-kernel@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Andrii Nakryiko <andrii@...nel.org>,
        Björn Töpel <bjorn@...nel.org>,
        Luke Nelson <luke.r.nels@...il.com>,
        Xi Wang <xi.wang@...il.com>, Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>
Subject: Re: [PATCH bpf-next v3 4/6] libbpf: Unify memory address casting
 operation style



On 2022/7/9 6:30, Andrii Nakryiko wrote:
> On Thu, Jul 7, 2022 at 5:23 AM Pu Lehui <pulehui@...wei.com> wrote:
>>
>>
>>
>> On 2022/6/4 5:03, Andrii Nakryiko wrote:
>>> On Mon, May 30, 2022 at 2:03 PM Daniel Borkmann <daniel@...earbox.net> wrote:
>>>>
>>>> On 5/30/22 11:28 AM, Pu Lehui wrote:
>>>>> The members of bpf_prog_info, which are line_info, jited_line_info,
>>>>> jited_ksyms and jited_func_lens, store u64 address pointed to the
>>>>> corresponding memory regions. Memory addresses are conceptually
>>>>> unsigned, (unsigned long) casting makes more sense, so let's make
>>>>> a change for conceptual uniformity.
>>>>>
>>>>> Signed-off-by: Pu Lehui <pulehui@...wei.com>
>>>>> ---
>>>>>     tools/lib/bpf/bpf_prog_linfo.c | 9 +++++----
>>>>>     1 file changed, 5 insertions(+), 4 deletions(-)
>>>>>
>>>>> diff --git a/tools/lib/bpf/bpf_prog_linfo.c b/tools/lib/bpf/bpf_prog_linfo.c
>>>>> index 5c503096ef43..7beb060d0671 100644
>>>>> --- a/tools/lib/bpf/bpf_prog_linfo.c
>>>>> +++ b/tools/lib/bpf/bpf_prog_linfo.c
>>>>> @@ -127,7 +127,8 @@ struct bpf_prog_linfo *bpf_prog_linfo__new(const struct bpf_prog_info *info)
>>>>>         prog_linfo->raw_linfo = malloc(data_sz);
>>>>>         if (!prog_linfo->raw_linfo)
>>>>>                 goto err_free;
>>>>> -     memcpy(prog_linfo->raw_linfo, (void *)(long)info->line_info, data_sz);
>>>>> +     memcpy(prog_linfo->raw_linfo, (void *)(unsigned long)info->line_info,
>>>>> +            data_sz);
>>>>
>>>> Took in patch 1-3, lgtm, thanks! My question around the cleanups in patch 4-6 ...
>>>> there are various other such cases e.g. in libbpf, perhaps makes sense to clean all
>>>> of them up at once and not just the 4 locations in here.
>>>
>>> if (void *)(long) pattern is wrong, then I guess the best replacement
>>> should be (void *)(uintptr_t) ?
>>>
>>
>> I also think that (void *)(uintptr_t) would be the best replacement. I
>> applied the changes to kernel/bpf and samples/bpf, and it worked fine.
>> But in selftests/bpf, the following similar error occur at compile time:
>>
>> progs/test_cls_redirect.c:504:11: error: cast to 'uint8_t *' (aka
>> 'unsigned char *') from smaller integer type 'uintptr_t' (aka 'unsigned
>> int') [-Werror,-Wint-to-pointer-cast]
>>          .head = (uint8_t *)(uintptr_t)skb->data,
> 
> this is BPF-side code so using system's uintptr_t definition won't
> work correctly here. Just do (unsigned long) instead?
> 

It is fine by me, and for this cleanup

>>
>> I take clang to compile with the front and back end separation, like
>> samples/bpf, and it works. It seems that the all-in-one clang has
>> problems handling the uintptr_t.
>>
>>>>
>>>> Thanks,
>>>> Daniel
>>> .
>>>
> .
>