linux-kernel - Re: [PATCH v9 perf,bpf 04/15] perf, bpf: synthesize bpf events with bpf_program__get_prog_info

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Message-ID: <741F3DF8-F95F-4521-BD46-B31A675D8E76@fb.com>
Date:   Thu, 14 Mar 2019 16:45:22 +0000
From:   Song Liu <songliubraving@...com>
To:     Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
CC:     "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
        Networking <netdev@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        "Alexei Starovoitov" <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        "Kernel Team" <Kernel-team@...com>,
        Peter Zijlstra <peterz@...radead.org>,
        "Arnaldo Carvalho de Melo" <acme@...hat.com>,
        "jolsa@...nel.org" <jolsa@...nel.org>,
        "namhyung@...nel.org" <namhyung@...nel.org>,
        "sdf@...ichev.me" <sdf@...ichev.me>
Subject: Re: [PATCH v9 perf,bpf 04/15] perf, bpf: synthesize bpf events with
 bpf_program__get_prog_info_linear()



> On Mar 13, 2019, at 10:08 PM, Song Liu <songliubraving@...com> wrote:
> 
> 
> 
>> On Mar 13, 2019, at 2:08 PM, Arnaldo Carvalho de Melo <arnaldo.melo@...il.com> wrote:
>> 
>> Em Wed, Mar 13, 2019 at 06:00:30PM -0300, Arnaldo Carvalho de Melo escreveu:
>>> Em Mon, Mar 11, 2019 at 10:30:40PM -0700, Song Liu escreveu:
>>>> -
>>>> 	/* Synthesize PERF_RECORD_KSYMBOL */
>>>> 	for (i = 0; i < sub_prog_cnt; i++) {
>>>> +		u8 (*prog_tags)[BPF_TAG_SIZE] = (void *)(info->prog_tags);
>>> 
>>> Need this:
>>> 
>>> -               u8 (*prog_tags)[BPF_TAG_SIZE] = (void *)(info->prog_tags);
>>> +               u8 (*prog_tags)[BPF_TAG_SIZE] = (u8 *)(info->prog_tags);
>>> 
>>> 
>>> To overcome this on debian:experimental-x-mips, i.e. Debian Experimental
>>> cross building to MIPS 32-bit:
>>> 
>>> util/bpf-event.c: In function 'perf_event__synthesize_one_bpf_prog':
>>> util/bpf-event.c:143:35: error: cast to pointer from integer of different size [-Werror=int-to-pointer-cast]
>>>  u8 (*prog_tags)[BPF_TAG_SIZE] = (void *)(info->prog_tags);
>>>                                  ^
>>> util/bpf-event.c:144:22: error: cast to pointer from integer of different size [-Werror=int-to-pointer-cast]
>>>  __u32 *prog_lens = (__u32 *)(info->jited_func_lens);
>>>                     ^
>>> util/bpf-event.c:145:23: error: cast to pointer from integer of different size [-Werror=int-to-pointer-cast]
>>>  __u64 *prog_addrs = (__u64 *)(info->jited_ksyms);
>>>                      ^
>>> util/bpf-event.c:146:22: error: cast to pointer from integer of different size [-Werror=int-to-pointer-cast]
>>>  void *func_infos = (void *)(info->func_info);
>>>                     ^
>>> CC       /tmp/build/perf/util/pmu.o
>>> CC       /tmp/build/perf/util/pmu-flex.o
>>> cc1: all warnings being treated as errors
>> 
>> Argh, hit the send button too fast, that is not the only case and then
>> my change just changed the error:
>> 
>> util/bpf-event.c: In function 'perf_event__synthesize_one_bpf_prog':
>> util/bpf-event.c:143:35: error: cast to pointer from integer of different size [-Werror=int-to-pointer-cast]
>>  u8 (*prog_tags)[BPF_TAG_SIZE] = (u8 *)(info->prog_tags);
>>                                  ^
>> util/bpf-event.c:143:35: error: initialization of 'u8 (*)[8]' {aka 'unsigned char (*)[8]'} from incompatible pointer type 'u8 *' {aka 'unsigned char *'} [-Werror=incompatible-pointer-types]
>> util/bpf-event.c:144:22: error: cast to pointer from integer of different size [-Werror=int-to-pointer-cast]
>>  __u32 *prog_lens = (__u32 *)(info->jited_func_lens);
>>                     ^
>> util/bpf-event.c:145:23: error: cast to pointer from integer of different size [-Werror=int-to-pointer-cast]
>>  __u64 *prog_addrs = (__u64 *)(info->jited_ksyms);
>>                      ^
>> util/bpf-event.c:146:22: error: cast to pointer from integer of different size [-Werror=int-to-pointer-cast]
>>  void *func_infos = (void *)(info->func_info);
>>                     ^
>> CC       /tmp/build/perf/util/pmu.o
>> CC       /tmp/build/perf/util/pmu-flex.o
>> cc1: all warnings being treated as errors
>> mv: cannot stat '/tmp/build/perf/util/.bpf-event.o.tmp': No such file or directory
>> 
> 
> We can fix it with the following:
> 
> -               u8 (*prog_tags)[BPF_TAG_SIZE] = (void *)(info->prog_tags);
> -               __u32 *prog_lens = (__u32 *)(info->jited_func_lens);
> -               __u64 *prog_addrs = (__u64 *)(info->jited_ksyms);
> -               void *func_infos = (void *)(info->func_info);
> +               u8 (*prog_tags)[BPF_TAG_SIZE] = (void *)(intptr_t)(info->prog_tags);
> +               __u32 *prog_lens = (__u32 *)(intptr_t)(info->jited_func_lens);
> +               __u64 *prog_addrs = (__u64 *)(intptr_t)(info->jited_ksyms);
> +               void *func_infos = (void *)(intptr_t)(info->func_info);
> 
> Thanks,
> Song

Actually, I think uintptr_t is better than intptr_t here. 

Thanks,
Song