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

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Message-ID: <20241214002938.1027546-1-namhyung@kernel.org>
Date: Fri, 13 Dec 2024 16:29:38 -0800
From: Namhyung Kim <namhyung@...nel.org>
To: Arnaldo Carvalho de Melo <acme@...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: [PATCH] perf ftrace latency: Fix compiler error for clang 12

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>
---
 tools/perf/util/bpf_skel/func_latency.bpf.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/tools/perf/util/bpf_skel/func_latency.bpf.c b/tools/perf/util/bpf_skel/func_latency.bpf.c
index 50ae153bf26e7a13..4df54e1b1411b10a 100644
--- a/tools/perf/util/bpf_skel/func_latency.bpf.c
+++ b/tools/perf/util/bpf_skel/func_latency.bpf.c
@@ -116,7 +116,8 @@ int BPF_PROG(func_end)
 			// Less than 1 unit (ms or ns), or, in the future,
 			// than the min latency desired.
 			if (delta > 0) { // 1st entry: [ 1 unit .. bucket_range units )
-				key = delta / bucket_range + 1;
+				// clang 12 doesn't like s64 / u32 division
+				key = (__u64)delta / bucket_range + 1;
 				if (key >= NUM_BUCKET ||
 					delta >= max_latency - min_latency)
 					key = NUM_BUCKET - 1;
-- 
2.47.1.613.gc27f4b7a9f-goog