linux-kernel - [PATCH] perf tools: Fixup module symbol end address properly

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Date: Mon, 12 Feb 2024 15:33:22 -0800
From: Namhyung Kim <namhyung@...nel.org>
To: Arnaldo Carvalho de Melo <acme@...nel.org>,
	Ian Rogers <irogers@...gle.com>
Cc: 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,
	Leo Yan <leo.yan@...ux.dev>,
	Will Deacon <will@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	John Garry <john.g.garry@...cle.com>,
	Mike Leach <mike.leach@...aro.org>
Subject: [PATCH] perf tools: Fixup module symbol end address properly

I got a strange error on ARM to fail on processing FINISHED_ROUND
record.  It turned out that it was failing in symbol__alloc_hist()
because the symbol size is too big.

When a sample is captured on a specific BPF program, it failed.  I've
added a debug code and found the end address of the symbol is from
the next module which is placed far way.

  ffff800008795778-ffff80000879d6d8: bpf_prog_1bac53b8aac4bc58_netcg_sock    [bpf]
  ffff80000879d6d8-ffff80000ad656b4: bpf_prog_76867454b5944e15_netcg_getsockopt      [bpf]
  ffff80000ad656b4-ffffd69b7af74048: bpf_prog_1d50286d2eb1be85_hn_egress     [bpf]   <---------- here
  ffffd69b7af74048-ffffd69b7af74048: $x.5    [sha3_generic]
  ffffd69b7af74048-ffffd69b7af740b8: crypto_sha3_init        [sha3_generic]
  ffffd69b7af740b8-ffffd69b7af741e0: crypto_sha3_update      [sha3_generic]

The logic in symbols__fixup_end() just uses curr->start to update the
prev->end.  But in this case, it won't work as it's too different.

I think ARM has a different kernel memory layout for modules and BPF
than on x86.  Actually there's a logic to handle kernel and module
boundary.  Let's do the same for symbols between different modules.

Signed-off-by: Namhyung Kim <namhyung@...nel.org>
---
 tools/perf/util/symbol.c | 21 +++++++++++++++++++--
 1 file changed, 19 insertions(+), 2 deletions(-)

diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c
index 35975189999b..9ebdb8e13c0b 100644
--- a/tools/perf/util/symbol.c
+++ b/tools/perf/util/symbol.c
@@ -248,14 +248,31 @@ void symbols__fixup_end(struct rb_root_cached *symbols, bool is_kallsyms)
 		 * segment is very big.  Therefore do not fill this gap and do
 		 * not assign it to the kernel dso map (kallsyms).
 		 *
+		 * Also BPF code can be allocated separately from text segments
+		 * and modules.  So the last entry in a module should not fill
+		 * the gap too.
+		 *
 		 * In kallsyms, it determines module symbols using '[' character
 		 * like in:
 		 *   ffffffffc1937000 T hdmi_driver_init  [snd_hda_codec_hdmi]
 		 */
 		if (prev->end == prev->start) {
+			const char *prev_mod;
+			const char *curr_mod;
+
+			if (!is_kallsyms) {
+				prev->end = curr->start;
+				continue;
+			}
+
+			prev_mod = strchr(prev->name, '[');
+			curr_mod = strchr(curr->name, '[');
+
 			/* Last kernel/module symbol mapped to end of page */
-			if (is_kallsyms && (!strchr(prev->name, '[') !=
-					    !strchr(curr->name, '[')))
+			if (!prev_mod != !curr_mod)
+				prev->end = roundup(prev->end + 4096, 4096);
+			/* Last symbol in the previous module */
+			else if (prev_mod && strcmp(prev_mod, curr_mod))
 				prev->end = roundup(prev->end + 4096, 4096);
 			else
 				prev->end = curr->start;
-- 
2.43.0.687.g38aa6559b0-goog