perf c2c: add function view model skeleton

Add the initial common model for the c2c function view: model state and
small helpers shared by the hierarchy construction and formatting added
in later patches.

Build the model from util/ so it remains independent of the TUI and
command-private symbols.

Signed-off-by: Jiebin Sun <jiebin.sun@intel.com>
Reviewed-by: Tianyou Li <tianyou.li@intel.com>
Reviewed-by: Wangyang Guo <wangyang.guo@intel.com>
Reviewed-by: Ian Rogers <irogers@google.com>
Cc: Dapeng Mi <dapeng1.mi@linux.intel.com>
Cc: James Clark <james.clark@linaro.org>
Cc: Thomas Falcon <thomas.falcon@intel.com>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>

tools/perf/util/Build

@@ -12,6 +12,7 @@ perf-util-y += block-info.o
 perf-util-y += block-range.o
 perf-util-y += build-id.o
 perf-util-y += c2c.o
+perf-util-y += c2c-function.o
 perf-util-y += cacheline.o
 perf-util-$(CONFIG_LIBCAPSTONE) += capstone.o
 perf-util-y += config.o

tools/perf/util/c2c-function.c

@@ -0,0 +1,66 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * C2C function model - function-level cacheline sharing analysis
+ *
+ * Displays a 3-level hierarchy showing which functions share cachelines:
+ *   Level 1: Read-side functions sorted by Cycles % (estimated load cycles)
+ *   Level 2: Functions sampled writing the shared lines read by level 1
+ *   Level 3: The specific cachelines where the two functions contend
+ *
+ * Builds the hierarchy from the existing cacheline histograms
+ * (c2c_hist_entry->hists), reusing the shared c2c data structures.
+ */
+
+#include <errno.h>
+#include <inttypes.h>
+#include <stdlib.h>
+#include <string.h>
+#include <tools/libc_compat.h> /* reallocarray */
+#include <linux/list.h>
+#include <linux/rbtree.h>
+#include <linux/zalloc.h>
+
+#include "addr_location.h"
+#include "c2c.h"
+#include "cacheline.h"
+#include "hist.h"
+#include "map.h"
+#include "mem-events.h"
+#include "mem-info.h"
+#include "sort.h"
+#include "symbol.h"
+#include "thread.h"
+
+struct c2c_function_model {
+	struct c2c_hists	function_hists;
+	/* Total estimated cycles across all level-1 entries. */
+	u64			total_cycles;
+	/* Source cacheline histograms; not owned here. */
+	struct c2c_hists	*cl_hists;
+	/* --coalesce field list, used to require iaddr. */
+	const char		*cl_sort;
+	/* Do not cap long symbol names. */
+	bool			 symbol_full;
+};
+
+static struct c2c_function_model c2c_ext __maybe_unused;
+
+static inline __maybe_unused u64 c2c_hitm_count(const struct c2c_stats *stats)
+{
+	return stats->tot_hitm;
+}
+
+static inline __maybe_unused bool symbol_name_equal(struct symbol *a, struct symbol *b)
+{
+	/* Two unknown symbols compare equal, matching cmp_null() in util/sort.c. */
+	if (!a || !b)
+		return a == b;
+	return arch__compare_symbol_names(a->name, b->name) == 0;
+}
+
+static inline __maybe_unused u64 hist_entry__iaddr(struct hist_entry *he)
+{
+	if (he->mem_info)
+		return mem_info__iaddr(he->mem_info)->addr;
+	return he->ip;
+}