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

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Date:   Thu, 7 Jul 2022 20:23:00 +0800
From:   Pu Lehui <pulehui@...wei.com>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>,
        Daniel Borkmann <daniel@...earbox.net>
CC:     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 2022/6/4 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,

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
> .
>