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From:   olsajiri@gmail.com
Date:   Tue, 28 Jun 2022 10:17:10 +0200
Cc:     Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
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        Stephane Eranian <eranian@google.com>
Subject: Re: [PATCH] perf bpf: 8 byte align bpil data
Message-ID: <Yrq5Bun3Nmb1vrW3@krava>
References: <20220614014714.1407239-1-irogers@google.com>
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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'

> 
> $ 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@krava 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

thanks,
jirka