Re: [PATCH v9 perf,bpf 04/15] perf, bpf: synthesize bpf events with bpf_program__get_prog_info_linear()

From: Arnaldo Carvalho de Melo <arnaldo.melo@gmail.com>
To: Song Liu <songliubraving@fb.com>
Cc: Arnaldo Carvalho de Melo <arnaldo.melo@gmail.com>,
	"bpf@vger.kernel.org" <bpf@vger.kernel.org>,
	Networking <netdev@vger.kernel.org>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Kernel Team <Kernel-team@fb.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Arnaldo Carvalho de Melo <acme@redhat.com>,
	"jolsa@kernel.org" <jolsa@kernel.org>,
	"namhyung@kernel.org" <namhyung@kernel.org>,
	"sdf@fomichev.me" <sdf@fomichev.me>
Subject: Re: [PATCH v9 perf,bpf 04/15] perf, bpf: synthesize bpf events with bpf_program__get_prog_info_linear()
Date: Thu, 14 Mar 2019 15:30:51 -0300	[thread overview]
Message-ID: <20190314183051.GA956@kernel.org> (raw)
In-Reply-To: <741F3DF8-F95F-4521-BD46-B31A675D8E76@fb.com>

Em Thu, Mar 14, 2019 at 04:45:22PM +0000, Song Liu escreveu:
> > On Mar 13, 2019, at 10:08 PM, Song Liu <songliubraving@fb.com> wrote:
> >> On Mar 13, 2019, at 2:08 PM, Arnaldo Carvalho de Melo <arnaldo.melo@gmail.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);

> >> 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);

> >> 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);

> Actually, I think uintptr_t is better than intptr_t here. 

Yeap, did the trick:

$ dm debian:experimental-x-mips
   1   debian:experimental-x-mips    : Ok   mips-linux-gnu-gcc (Debian 8.3.0-2) 8.3.0
$

Works as well with x86_64 with a recent distro such as fedora:30 or
ubuntu:19.04, building it with both gcc and clang:

$ dm fedora:30 ubuntu:19.04
   1 fedora:30    : Ok   gcc (GCC) 9.0.1 20190227 (Red Hat 9.0.1-0.8), clang version 8.0.0 (Fedora 8.0.0-0.5.rc3.fc30)
   2 ubuntu:19.04 : Ok   gcc (Ubuntu 8.3.0-2ubuntu2) 8.3.0, clang version 8.0.0-+rc4-1ubuntu1 (tags/RELEASE_800/rc4)
$

Continuing with the review/tests...

- Arnaldo