linux-kernel - Re: [PATCH bpf-next 5/5] selftests/bpf: Remove the casting about jited_ksyms and jited

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Message-ID: <90d2c163-0900-0eb7-6d5c-c6e7ab530fa1@huawei.com>
Date:   Mon, 18 Jul 2022 19:57:32 +0800
From:   Pu Lehui <pulehui@...wei.com>
To:     Yonghong Song <yhs@...com>, <bpf@...r.kernel.org>,
        <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>
CC:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Quentin Monnet <quentin@...valent.com>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>
Subject: Re: [PATCH bpf-next 5/5] selftests/bpf: Remove the casting about
 jited_ksyms and jited_linfo



On 2022/7/17 9:46, Yonghong Song wrote:
> 
> 
> On 7/16/22 5:51 AM, Pu Lehui wrote:
>> We have unified data extension operation of jited_ksyms and jited_linfo
>> into zero extension, so there's no need to cast u64 memory address to
>> long data type.
> 
> For subject, we are not 'Remove the casting ...'. What the code did is
> to change the casting.
> 
> Also, I don't understand the above commit message. What does this mean
> about 'data extension operation of jited_ksyms and jited_linfo into zero 
> extension'?
> 
> In prog_tests/btf.c, we have a few other places to cast 
> jited_linfo[...]/jited_ksyms[...] to 'long' type. Maybe casting
> to 'unsigned long' is a better choice. Casting to 'unsigned long long'
> of course will work, but is it necessary? Or you are talking about
> 64bit kernel and 32bit user space?
> 

Hi Yonghong,

Thanks for your review. We introduced riscv jited line info in series 
[0], and we found that 32-bit systems can not display bpf line info due 
to the inconsistent data extension between jited_ksyms and jited_linfo. 
And we finally unify them to zero extension. By the way, we cleanup the 
related code. jited_ksyms and jited_linfo both are u64 address, no need 
to casting to long, and we previously remove it. But u64 in some arch is 
%ld, so to avoid compiler warnings we just cast to unsigned long long.

And sorry for not updating the subject and comment. I will corret it.

[0] 
https://lore.kernel.org/bpf/CAEf4Bza4RT=KFhr9ev29967dyT0eF_+6ZRqK35beUvnA_NbcqQ@mail.gmail.com/

>>
>> Signed-off-by: Pu Lehui <pulehui@...wei.com>
>> ---
>>   tools/testing/selftests/bpf/prog_tests/btf.c | 16 +++++++++-------
>>   1 file changed, 9 insertions(+), 7 deletions(-)
>>
>> diff --git a/tools/testing/selftests/bpf/prog_tests/btf.c 
>> b/tools/testing/selftests/bpf/prog_tests/btf.c
>> index e852a9df779d..db10fa1745d1 100644
>> --- a/tools/testing/selftests/bpf/prog_tests/btf.c
>> +++ b/tools/testing/selftests/bpf/prog_tests/btf.c
>> @@ -6613,8 +6613,9 @@ static int test_get_linfo(const struct 
>> prog_info_raw_test *test,
>>       }
>>       if (CHECK(jited_linfo[0] != jited_ksyms[0],
>> -          "jited_linfo[0]:%lx != jited_ksyms[0]:%lx",
>> -          (long)(jited_linfo[0]), (long)(jited_ksyms[0]))) {
>> +          "jited_linfo[0]:%llx != jited_ksyms[0]:%llx",
>> +          (unsigned long long)(jited_linfo[0]),
>> +          (unsigned long long)(jited_ksyms[0]))) {
>>           err = -1;
>>           goto done;
>>       }
>> @@ -6632,16 +6633,17 @@ static int test_get_linfo(const struct 
>> prog_info_raw_test *test,
>>           }
>>           if (CHECK(jited_linfo[i] <= jited_linfo[i - 1],
>> -              "jited_linfo[%u]:%lx <= jited_linfo[%u]:%lx",
>> -              i, (long)jited_linfo[i],
>> -              i - 1, (long)(jited_linfo[i - 1]))) {
>> +              "jited_linfo[%u]:%llx <= jited_linfo[%u]:%llx",
>> +              i, (unsigned long long)jited_linfo[i],
>> +              i - 1, (unsigned long long)(jited_linfo[i - 1]))) {
>>               err = -1;
>>               goto done;
>>           }
>>           if (CHECK(jited_linfo[i] - cur_func_ksyms > cur_func_len,
>> -              "jited_linfo[%u]:%lx - %lx > %u",
>> -              i, (long)jited_linfo[i], (long)cur_func_ksyms,
>> +              "jited_linfo[%u]:%llx - %llx > %u",
>> +              i, (unsigned long long)jited_linfo[i],
>> +              (unsigned long long)cur_func_ksyms,
>>                 cur_func_len)) {
>>               err = -1;
>>               goto done;
> .