[PATCH bpf-next 4/5] selftests/bpf: Add arena-based bitmap data structure

[Emil Tsalapatis <emil@etsalapatis.com>]

Add an arena-based word-aligned bitmap data struture. The
structure is useful as a building block, e.g., sched-ext
uses it to represent cpumask structures.

Signed-off-by: Emil Tsalapatis <emil@etsalapatis.com>
---
 .../bpf/libarena/include/libarena/bitmap.h    |  31 +++
 .../selftests/bpf/libarena/src/bitmap.bpf.c   | 191 ++++++++++++++++++
 2 files changed, 222 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/libarena/include/libarena/bitmap.h
 create mode 100644 tools/testing/selftests/bpf/libarena/src/bitmap.bpf.c

diff --git a/tools/testing/selftests/bpf/libarena/include/libarena/bitmap.h b/tools/testing/selftests/bpf/libarena/include/libarena/bitmap.h
new file mode 100644
index 000000000000..11623a82e66a
--- /dev/null
+++ b/tools/testing/selftests/bpf/libarena/include/libarena/bitmap.h
@@ -0,0 +1,31 @@
+#pragma once
+
+#define BITS_PER_BYTE		8
+#define BYTES_TO_BITS(nb)	((nb) * BITS_PER_BYTE)
+
+#define BITS_PER_LONG		(sizeof(long) * BITS_PER_BYTE)
+#define BITS_TO_LONGS(nr)	(((nr) + BITS_PER_LONG - 1) / BITS_PER_LONG)
+#define BIT_MASK(nr)		(1UL << ((nr) % BITS_PER_LONG))
+#define BIT_WORD(nr)		((nr) / BITS_PER_LONG)
+
+struct bitmap {
+	u64 bits[0];
+};
+
+struct bitmap __arena *bmp_alloc(size_t bits);
+void bmp_free(struct bitmap __arena *bmp);
+
+void bmp_set_bit(u32 bit, struct bitmap __arena *bmp);
+void bmp_clear_bit(u32 bit, struct bitmap __arena *bmp);
+bool bmp_test_bit(u32 bit, struct bitmap __arena *bmp);
+bool bmp_test_and_clear_bit(u32 bit, struct bitmap __arena *bmp);
+
+void bmp_clear(size_t bits, struct bitmap __arena *bmp);
+void bmp_and(size_t bits, struct bitmap __arena *dst, struct bitmap __arena *src1, struct bitmap __arena *src2);
+void bmp_or(size_t bits, struct bitmap __arena *dst, struct bitmap __arena *src1, struct bitmap __arena *src2);
+bool bmp_empty(size_t bits, struct bitmap __arena *bmp);
+void bmp_copy(size_t bits, struct bitmap __arena *dst, struct bitmap __arena *src);
+
+bool bmp_intersects(size_t bits, struct bitmap __arena *arg1, struct bitmap __arena *arg2);
+bool bmp_subset(size_t bits, struct bitmap __arena *big, struct bitmap __arena *small);
+void bmp_print(size_t bits, struct bitmap __arena *bmp);
diff --git a/tools/testing/selftests/bpf/libarena/src/bitmap.bpf.c b/tools/testing/selftests/bpf/libarena/src/bitmap.bpf.c
new file mode 100644
index 000000000000..a8ca814aa0c8
--- /dev/null
+++ b/tools/testing/selftests/bpf/libarena/src/bitmap.bpf.c
@@ -0,0 +1,191 @@
+// SPDX-License-Identifier: LGPL-2.1 OR BSD-2-Clause
+/*
+ * Copyright (c) 2025-2026 Meta Platforms, Inc. and affiliates.
+ * Copyright (c) 2025-2026 Emil Tsalapatis <emil@etsalapatis.com>
+ */
+
+#include <libarena/common.h>
+
+#include <libarena/asan.h>
+#include <libarena/bitmap.h>
+
+__weak
+struct bitmap __arena *bmp_alloc(size_t bits)
+{
+	struct bitmap __arena *bmp;
+	size_t size = BITS_TO_LONGS(bits) * sizeof(bmp->bits[0]);
+
+	/* Assume long-aligned masks. */
+	if (bits % BITS_PER_LONG)
+		return NULL;
+
+	bmp = (struct bitmap __arena *)arena_malloc(size);
+	if (!bmp)
+		return NULL;
+
+	bmp_clear(bits, bmp);
+
+	return bmp;
+}
+
+__weak
+void bmp_free(struct bitmap __arena *bmp)
+{
+	arena_free(bmp);
+}
+
+__weak
+void bmp_set_bit(u32 bit, struct bitmap __arena *bmp)
+{
+	bmp->bits[BIT_WORD(bit)] |= BIT_MASK(bit);
+}
+
+__weak
+void bmp_clear_bit(u32 bit, struct bitmap __arena *bmp)
+{
+	bmp->bits[BIT_WORD(bit)] &= ~BIT_MASK(bit);
+}
+
+__weak
+bool bmp_test_bit(u32 bit, struct bitmap __arena *bmp)
+{
+	return bmp->bits[BIT_WORD(bit)] & BIT_MASK(bit);
+}
+
+__weak
+bool bmp_test_and_clear_bit(u32 bit, struct bitmap __arena *bmp)
+{
+	u64 val = BIT_MASK(bit);
+	u32 idx = BIT_WORD(bit);
+	u64 actual;
+
+	do {
+		u64 old = bmp->bits[idx];
+
+		if (!(old & val))
+			return false;
+
+		u64 new = old & ~val;
+		actual = cmpxchg(&bmp->bits[idx], old, new);
+
+		if (actual == old)
+			return true;
+
+	} while (can_loop);
+
+	return false;
+}
+
+__weak
+void bmp_clear(size_t bits, struct bitmap __arena *bmp)
+{
+	size_t nwords = BITS_TO_LONGS(bits);
+	volatile u32 i;
+
+	for (i = zero; i < nwords && can_loop; i++)
+		bmp->bits[i] = 0;
+}
+
+static __always_inline u64 bmp_last_word_mask(size_t bits)
+{
+	u32 rem = bits % BITS_PER_LONG;
+
+	return rem ? (1ULL << rem) - 1 : ~0ULL;
+}
+
+__weak
+void bmp_and(size_t bits, struct bitmap __arena *dst, struct bitmap __arena *src1, struct bitmap __arena *src2)
+{
+	size_t nwords = BITS_TO_LONGS(bits);
+	volatile u32 i;
+
+	for (i = zero; i < nwords && can_loop; i++)
+		dst->bits[i] = src1->bits[i] & src2->bits[i];
+
+	if (nwords && bits % BITS_PER_LONG)
+		dst->bits[nwords - 1] &= bmp_last_word_mask(bits);
+}
+
+__weak
+void bmp_or(size_t bits, struct bitmap __arena *dst, struct bitmap __arena *src1, struct bitmap __arena *src2)
+{
+	size_t nwords = BITS_TO_LONGS(bits);
+	volatile u32 i;
+
+	for (i = zero; i < nwords && can_loop; i++)
+		dst->bits[i] = src1->bits[i] | src2->bits[i];
+
+	if (nwords && bits % BITS_PER_LONG)
+		dst->bits[nwords - 1] &= bmp_last_word_mask(bits);
+}
+
+__weak
+bool bmp_empty(size_t bits, struct bitmap __arena *bmp)
+{
+	size_t nwords = BITS_TO_LONGS(bits);
+	volatile u32 i;
+
+	for (i = zero; i < nwords && can_loop; i++) {
+		u64 mask = (i == nwords - 1) ? bmp_last_word_mask(bits) : ~0ULL;
+
+		if (bmp->bits[i] & mask)
+			return false;
+	}
+
+	return true;
+}
+
+__weak
+void bmp_copy(size_t bits, struct bitmap __arena *dst, struct bitmap __arena *src)
+{
+	size_t nwords = BITS_TO_LONGS(bits);
+	volatile u32 i;
+
+	for (i = zero; i < nwords && can_loop; i++)
+		dst->bits[i] = src->bits[i];
+
+	if (nwords && bits % BITS_PER_LONG)
+		dst->bits[nwords - 1] &= bmp_last_word_mask(bits);
+}
+
+__weak
+bool bmp_subset(size_t bits, struct bitmap __arena *big, struct bitmap __arena *small)
+{
+	size_t nwords = BITS_TO_LONGS(bits);
+	volatile u32 i;
+
+	for (i = zero; i < nwords && can_loop; i++) {
+		u64 mask = (i == nwords - 1) ? bmp_last_word_mask(bits) : ~0ULL;
+
+		if (~big->bits[i] & small->bits[i] & mask)
+			return false;
+	}
+
+	return true;
+}
+
+__weak
+bool bmp_intersects(size_t bits, struct bitmap __arena *arg1, struct bitmap __arena *arg2)
+{
+	size_t nwords = BITS_TO_LONGS(bits);
+	volatile u32 i;
+
+	for (i = zero; i < nwords && can_loop; i++) {
+		u64 mask = (i == nwords - 1) ? bmp_last_word_mask(bits) : ~0ULL;
+
+		if (arg1->bits[i] & arg2->bits[i] & mask)
+			return true;
+	}
+
+	return false;
+}
+
+__weak
+void bmp_print(size_t bits, struct bitmap __arena *bmp)
+{
+	size_t nwords = BITS_TO_LONGS(bits);
+	volatile u32 i;
+
+	for (i = zero; i < nwords && can_loop; i++)
+		arena_stderr("%016llx ", bmp->bits[i]);
+}
-- 
2.54.0