linux-kernel - Re: [PATCH] perf ftrace latency: Fix compiler error for clang 12

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Message-ID: <Z2BY1MAUrXPJs1Ak@x1>
Date: Mon, 16 Dec 2024 13:44:04 -0300
From: Arnaldo Carvalho de Melo <acme@...nel.org>
To: Namhyung Kim <namhyung@...nel.org>
Cc: Ian Rogers <irogers@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
	Adrian Hunter <adrian.hunter@...el.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>, LKML <linux-kernel@...r.kernel.org>,
	linux-perf-users@...r.kernel.org,
	Gabriele Monaco <gmonaco@...hat.com>
Subject: Re: [PATCH] perf ftrace latency: Fix compiler error for clang 12

On Fri, Dec 13, 2024 at 04:29:38PM -0800, Namhyung Kim wrote:
> I noticed this error on CentOS 8.
> 
>     CLANG   /build/util/bpf_skel/.tmp/func_latency.bpf.o
>   Error at line 119: Unsupport signed division for DAG: 0x55829ee68a10: i64 = sdiv 0x55829ee68bb0, 0x55829ee69090, util/bpf_skel/func_latency.bpf.c:119:17 @[ util/bpf_skel/func_latency.bpf.c:84:5 ]Please convert to unsigned div/mod.
>   fatal error: error in backend: Cannot select: 0x55829ee68a10: i64 = sdiv 0x55829ee68bb0, 0x55829ee69090, util/bpf_skel/func_latency.bpf.c:119:17 @[ util/bpf_skel/func_latency.bpf.c:84:5 ]
>     0x55829ee68bb0: i64,ch = CopyFromReg 0x55829edc9a78, Register:i64 %5, util/bpf_skel/func_latency.bpf.c:119:17 @[ util/bpf_skel/func_latency.bpf.c:84:5 ]
>       0x55829ee68e20: i64 = Register %5
>     0x55829ee69090: i64,ch = load<(volatile dereferenceable load 4 from @bucket_range, !tbaa !160), zext from i32> 0x55829edc9a78, 0x55829ee68fc0, undef:i64, util/bpf_skel/func_latency.bpf.c:119:19 @[ util/bpf_skel/func_latency.bpf.c:84:5 ]
>       0x55829ee68fc0: i64 = BPFISD::Wrapper TargetGlobalAddress:i64<i32* @bucket_range> 0, util/bpf_skel/func_latency.bpf.c:119:19 @[ util/bpf_skel/func_latency.bpf.c:84:5 ]
>         0x55829ee68808: i64 = TargetGlobalAddress<i32* @bucket_range> 0, util/bpf_skel/func_latency.bpf.c:119:19 @[ util/bpf_skel/func_latency.bpf.c:84:5 ]
>       0x55829ee68530: i64 = undef
>   In function: func_end
>   PLEASE submit a bug report to https://bugs.llvm.org/ and include the crash backtrace, preprocessed source, and associated run script.
> 
> It complains about sdiv which is (s64)delta / (u32)bucket_range.
> Let's cast the delta to u64 for division.
> 
> Fixes: e8536dd47a98b5db ("perf ftrace latency: Introduce --bucket-range to ask for linear bucketing")
> Cc: Gabriele Monaco <gmonaco@...hat.com>
> Signed-off-by: Namhyung Kim <namhyung@...nel.org>

Committer testing:

Tested on:

  $ head -2 /etc/os-release
  NAME="Fedora Linux"
  VERSION="40 (Toolbx Container Image)"
  $ clang --version |& head -1
  clang version 18.1.8 (Fedora 18.1.8-1.fc40)
  $
  root@...ber:~# perf ftrace latency --use-nsec --bucket-range=200 --min-latency 250 --max-latency=5000 -T switch_mm_irqs_off -a sleep 10
  #   DURATION     |      COUNT | GRAPH                                          |
       0 -  250 ns |         28 | #####                                          |
     250 -  450 ns |         12 | ##                                             |
     450 -  650 ns |         10 | #                                              |
     650 -  850 ns |          9 | #                                              |
     850 - 1050 ns |         20 | ###                                            |
    1.05 - 1.25 us |         14 | ##                                             |
    1.25 - 1.45 us |         16 | ###                                            |
    1.45 - 1.65 us |          8 | #                                              |
    1.65 - 1.85 us |         11 | ##                                             |
    1.85 - 2.05 us |          7 | #                                              |
    2.05 - 2.25 us |         11 | ##                                             |
    2.25 - 2.45 us |         10 | #                                              |
    2.45 - 2.65 us |          7 | #                                              |
    2.65 - 2.85 us |          8 | #                                              |
    2.85 - 3.05 us |          7 | #                                              |
    3.05 - 3.25 us |          7 | #                                              |
    3.25 - 3.45 us |         10 | #                                              |
    3.45 - 3.65 us |          5 |                                                |
    3.65 - 3.85 us |          9 | #                                              |
    3.85 - 4.05 us |          2 |                                                |
    4.05 - 4.25 us |          6 | #                                              |
    4.25 - ...  us |         23 | ####                                           |
  root@...ber:~#

Thanks, applied to perf-tools-next.

- Arnaldo