v4.19.13 snapshot.
diff --git a/tools/perf/util/pstack.c b/tools/perf/util/pstack.c
new file mode 100644
index 0000000..797fe1a
--- /dev/null
+++ b/tools/perf/util/pstack.c
@@ -0,0 +1,84 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Simple pointer stack
+ *
+ * (c) 2010 Arnaldo Carvalho de Melo <acme@redhat.com>
+ */
+
+#include "util.h"
+#include "pstack.h"
+#include "debug.h"
+#include <linux/kernel.h>
+#include <stdlib.h>
+
+struct pstack {
+ unsigned short top;
+ unsigned short max_nr_entries;
+ void *entries[0];
+};
+
+struct pstack *pstack__new(unsigned short max_nr_entries)
+{
+ struct pstack *pstack = zalloc((sizeof(*pstack) +
+ max_nr_entries * sizeof(void *)));
+ if (pstack != NULL)
+ pstack->max_nr_entries = max_nr_entries;
+ return pstack;
+}
+
+void pstack__delete(struct pstack *pstack)
+{
+ free(pstack);
+}
+
+bool pstack__empty(const struct pstack *pstack)
+{
+ return pstack->top == 0;
+}
+
+void pstack__remove(struct pstack *pstack, void *key)
+{
+ unsigned short i = pstack->top, last_index = pstack->top - 1;
+
+ while (i-- != 0) {
+ if (pstack->entries[i] == key) {
+ if (i < last_index)
+ memmove(pstack->entries + i,
+ pstack->entries + i + 1,
+ (last_index - i) * sizeof(void *));
+ --pstack->top;
+ return;
+ }
+ }
+ pr_err("%s: %p not on the pstack!\n", __func__, key);
+}
+
+void pstack__push(struct pstack *pstack, void *key)
+{
+ if (pstack->top == pstack->max_nr_entries) {
+ pr_err("%s: top=%d, overflow!\n", __func__, pstack->top);
+ return;
+ }
+ pstack->entries[pstack->top++] = key;
+}
+
+void *pstack__pop(struct pstack *pstack)
+{
+ void *ret;
+
+ if (pstack->top == 0) {
+ pr_err("%s: underflow!\n", __func__);
+ return NULL;
+ }
+
+ ret = pstack->entries[--pstack->top];
+ pstack->entries[pstack->top] = NULL;
+ return ret;
+}
+
+void *pstack__peek(struct pstack *pstack)
+{
+ if (pstack->top == 0)
+ return NULL;
+ return pstack->entries[pstack->top - 1];
+}