linux-kernel - Re: [PATCH] perf bpf: 8 byte align bpil data

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Date:   Tue, 28 Jun 2022 08:15:04 -0700
From:   Ian Rogers <irogers@...gle.com>
To:     olsajiri@...il.com
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        Dave Marchevsky <davemarchevsky@...com>,
        Quentin Monnet <quentin@...valent.com>,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org, bpf@...r.kernel.org,
        Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH] perf bpf: 8 byte align bpil data

On Tue, Jun 28, 2022 at 1:41 AM <olsajiri@...il.com> wrote:
>
> On Mon, Jun 13, 2022 at 06:47:14PM -0700, Ian Rogers wrote:
> > bpil data is accessed assuming 64-bit alignment resulting in undefined
> > behavior as the data is just byte aligned. With an -fsanitize=undefined
> > build the following errors are observed:
>
> I need to add -w to get the clean build with that, do you see that as well?
>
>   $ make EXTRA_CFLAGS='-fsanitize=undefined -w'

I don't recall needing this, but I was stacking fixes which may explain it.

> >
> > $ sudo perf record -a sleep 1
> > util/bpf-event.c:310:22: runtime error: load of misaligned address 0x55f61084520f for type '__u64', which requires 8 byte alignment
> > 0x55f61084520f: note: pointer points here
> >  a8 fe ff ff 3c  51 d3 c0 ff ff ff ff 04  84 d3 c0 ff ff ff ff d8  aa d3 c0 ff ff ff ff a4  c0 d3 c0
> >              ^
> > util/bpf-event.c:311:20: runtime error: load of misaligned address 0x55f61084522f for type '__u32', which requires 4 byte alignment
> > 0x55f61084522f: note: pointer points here
> >  ff ff ff ff c7  17 00 00 f1 02 00 00 1f  04 00 00 58 04 00 00 00  00 00 00 0f 00 00 00 63  02 00 00
> >              ^
> > util/bpf-event.c:198:33: runtime error: member access within misaligned address 0x55f61084523f for type 'const struct bpf_func_info', which requires 4 byte alignment
> > 0x55f61084523f: note: pointer points here
> >  58 04 00 00 00  00 00 00 0f 00 00 00 63  02 00 00 3b 00 00 00 ab  02 00 00 44 00 00 00 14  03 00 00
>
>
> and I'm also getting another error in:
>
> [root@...va perf]# ./perf record -a sleep 1
> util/synthetic-events.c:1202:11: runtime error: member access within misaligned address 0x00000286f7ea for type 'struct perf_record_record_cpu_map', which requires 8 byte alignment
> 0x00000286f7ea: note: pointer points here
>  20 00  01 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00 00 00
>               ^
> util/synthetic-events.c:1203:18: runtime error: member access within misaligned address 0x00000286f7ea for type 'struct perf_record_record_cpu_map', which requires 8 byte alignment
> 0x00000286f7ea: note: pointer points here
>  20 00  01 00 01 00 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00 00 00
>               ^
> util/synthetic-events.c:1206:46: runtime error: member access within misaligned address 0x00000286f7ea for type 'struct perf_record_record_cpu_map', which requires 8 byte alignment
> 0x00000286f7ea: note: pointer points here
>  20 00  01 00 01 00 08 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00 00 00
>               ^
> /home/jolsa/kernel/linux-perf/tools/include/asm-generic/bitops/atomic.h:10:29: runtime error: load of misaligned address 0x00000286f7f2 for type 'long unsigned int', which requires 8 byte alignment
> 0x00000286f7f2: note: pointer points here
>  00 00  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  51 00 00 00 00 00
>               ^
>
> are you going to address this one as well?
>
>
> the reason for this one is that 'data' in struct perf_record_cpu_map_data
> is not alligned(8), so that's why I raised the question in my other reply ;-)
>
> I wonder we should mark all tools/lib/perf/include/perf/event.h types
> as packed to prevent any compiler padding

I already sent out a fix and some improvements related to this:
https://lore.kernel.org/lkml/20220614143353.1559597-1-irogers@google.com/
Could you take a look?

I'm not sure about aligned and packed. I tried to minimize it in the
change above. The issue is that taking the address of a variable in a
packed struct results in an unaligned pointer. To address this in the
fix above I changed the functions to pass pointers to the whole
struct.

Thanks,
Ian

> thanks,
> jirka