linux-kernel - [PATCH 2/3] perf symbol: Update symbols__fixup

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Date:   Fri, 15 Apr 2022 17:40:47 -0700
From:   Namhyung Kim <namhyung@...nel.org>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Jiri Olsa <jolsa@...hat.com>, Ian Rogers <irogers@...gle.com>,
        Michael Petlan <mpetlan@...hat.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
        Song Liu <songliubraving@...com>,
        Will Deacon <will@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        John Garry <john.garry@...wei.com>,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        Leo Yan <leo.yan@...aro.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Heiko Carstens <hca@...ux.ibm.com>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-perf-users@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-s390@...r.kernel.org
Subject: [PATCH 2/3] perf symbol: Update symbols__fixup_end()

Now arch-specific functions all do the same thing.  When it fixes the
symbol address it needs to check the boundary between the kernel image
and modules.  For the last symbol in the previous region, it cannot
know the exact size as it's discarded already.  Thus it just uses a
small page size (4096) and rounds it up like the last symbol.

Signed-off-by: Namhyung Kim <namhyung@...nel.org>
---
 tools/perf/util/symbol.c | 29 +++++++++++++++++++++++++----
 1 file changed, 25 insertions(+), 4 deletions(-)

diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c
index 1b85cc1422a9..623094e866fd 100644
--- a/tools/perf/util/symbol.c
+++ b/tools/perf/util/symbol.c
@@ -217,8 +217,8 @@ void symbols__fixup_duplicate(struct rb_root_cached *symbols)
 	}
 }
 
-void symbols__fixup_end(struct rb_root_cached *symbols,
-			bool is_kallsyms __maybe_unused)
+/* Update zero-sized symbols using the address of the next symbol */
+void symbols__fixup_end(struct rb_root_cached *symbols, bool is_kallsyms)
 {
 	struct rb_node *nd, *prevnd = rb_first_cached(symbols);
 	struct symbol *curr, *prev;
@@ -232,8 +232,29 @@ void symbols__fixup_end(struct rb_root_cached *symbols,
 		prev = curr;
 		curr = rb_entry(nd, struct symbol, rb_node);
 
-		if (prev->end == prev->start || prev->end != curr->start)
-			arch__symbols__fixup_end(prev, curr);
+		/*
+		 * On some architecture kernel text segment start is located at
+		 * some low memory address, while modules are located at high
+		 * memory addresses (or vice versa).  The gap between end of
+		 * kernel text segment and beginning of first module's text
+		 * segment is very big.  Therefore do not fill this gap and do
+		 * not assign it to the kernel dso map (kallsyms).
+		 *
+		 * In kallsyms, it determines module symbols using '[' character
+		 * like in:
+		 *   ffffffffc1937000 T hdmi_driver_init  [snd_hda_codec_hdmi]
+		 */
+		if (prev->end == prev->start) {
+			/* Last kernel/module symbol mapped to end of page */
+			if (is_kallsyms && (!strchr(prev->name, '[') !=
+					    !strchr(curr->name, '[')))
+				prev->end = roundup(prev->end + 4096, 4096);
+			else
+				prev->end = curr->start;
+
+			pr_debug4("%s sym:%s end:%#" PRIx64 "\n",
+				  __func__, prev->name, prev->end);
+		}
 	}
 
 	/* Last entry */
-- 
2.36.0.rc0.470.gd361397f0d-goog