[RFC PATCH v4 7/7] selftests/bpf: Add test cases for btf__permute functionality

[Donglin Peng <dolinux.peng@gmail.com>]

From: pengdonglin <pengdonglin@xiaomi.com>

This patch introduces test cases for the btf__permute function to ensure
it works correctly with both base BTF and split BTF scenarios.

The test suite includes:
- test_permute_base: Validates permutation on standalone BTF
- test_permute_split: Tests permutation on split BTF with base dependencies

Each test verifies that type IDs are correctly rearranged and type
references are properly updated after permutation operations.

Cc: Eduard Zingerman <eddyz87@gmail.com>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Andrii Nakryiko <andrii.nakryiko@gmail.com>
Cc: Alan Maguire <alan.maguire@oracle.com>
Cc: Song Liu <song@kernel.org>
Signed-off-by: pengdonglin <pengdonglin@xiaomi.com>
Signed-off-by: Donglin Peng <dolinux.peng@gmail.com>
---
 .../selftests/bpf/prog_tests/btf_permute.c    | 142 ++++++++++++++++++
 1 file changed, 142 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/btf_permute.c

diff --git a/tools/testing/selftests/bpf/prog_tests/btf_permute.c b/tools/testing/selftests/bpf/prog_tests/btf_permute.c
new file mode 100644
index 000000000000..2692cef627ab
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/btf_permute.c
@@ -0,0 +1,142 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2025 Xiaomi */
+
+#include <test_progs.h>
+#include <bpf/btf.h>
+#include "btf_helpers.h"
+
+/* ensure btf__permute work as expected with base_btf */
+static void test_permute_base(void)
+{
+	struct btf *btf;
+	__u32 permute_ids[6];
+	int err;
+
+	btf = btf__new_empty();
+	if (!ASSERT_OK_PTR(btf, "empty_main_btf"))
+		return;
+
+	btf__add_int(btf, "int", 4, BTF_INT_SIGNED);	/* [1] int */
+	btf__add_ptr(btf, 1);				/* [2] ptr to int */
+	btf__add_struct(btf, "s1", 4);			/* [3] struct s1 { */
+	btf__add_field(btf, "m", 1, 0, 0);		/*       int m; */
+							/* } */
+	btf__add_struct(btf, "s2", 4);			/* [4] struct s2 { */
+	btf__add_field(btf, "m", 1, 0, 0);		/*       int m; */
+							/* } */
+	btf__add_func_proto(btf, 1);			/* [5] int (*)(int *p); */
+	btf__add_func_param(btf, "p", 2);
+	btf__add_func(btf, "f", BTF_FUNC_STATIC, 5);	/* [6] int f(int *p); */
+
+	VALIDATE_RAW_BTF(
+		btf,
+		"[1] INT 'int' size=4 bits_offset=0 nr_bits=32 encoding=SIGNED",
+		"[2] PTR '(anon)' type_id=1",
+		"[3] STRUCT 's1' size=4 vlen=1\n"
+		"\t'm' type_id=1 bits_offset=0",
+		"[4] STRUCT 's2' size=4 vlen=1\n"
+		"\t'm' type_id=1 bits_offset=0",
+		"[5] FUNC_PROTO '(anon)' ret_type_id=1 vlen=1\n"
+		"\t'p' type_id=2",
+		"[6] FUNC 'f' type_id=5 linkage=static");
+
+	permute_ids[0] = 4; /* struct s2 */
+	permute_ids[1] = 3; /* struct s1 */
+	permute_ids[2] = 5; /* int (*)(int *p) */
+	permute_ids[3] = 1; /* int */
+	permute_ids[4] = 6; /* int f(int *p) */
+	permute_ids[5] = 2; /* ptr to int */
+	err = btf__permute(btf, permute_ids, NULL);
+	if (!ASSERT_OK(err, "btf__permute"))
+		goto done;
+
+	VALIDATE_RAW_BTF(
+		btf,
+		"[1] STRUCT 's2' size=4 vlen=1\n"
+		"\t'm' type_id=4 bits_offset=0",
+		"[2] STRUCT 's1' size=4 vlen=1\n"
+		"\t'm' type_id=4 bits_offset=0",
+		"[3] FUNC_PROTO '(anon)' ret_type_id=4 vlen=1\n"
+		"\t'p' type_id=6",
+		"[4] INT 'int' size=4 bits_offset=0 nr_bits=32 encoding=SIGNED",
+		"[5] FUNC 'f' type_id=3 linkage=static",
+		"[6] PTR '(anon)' type_id=4");
+
+done:
+	btf__free(btf);
+}
+
+/* ensure btf__permute work as expected with split_btf */
+static void test_permute_split(void)
+{
+	struct btf *split_btf = NULL, *base_btf = NULL;
+	__u32 permute_ids[4];
+	int err;
+
+	base_btf = btf__new_empty();
+	if (!ASSERT_OK_PTR(base_btf, "empty_main_btf"))
+		return;
+
+	btf__add_int(base_btf, "int", 4, BTF_INT_SIGNED);	/* [1] int */
+	btf__add_ptr(base_btf, 1);				/* [2] ptr to int */
+	VALIDATE_RAW_BTF(
+		base_btf,
+		"[1] INT 'int' size=4 bits_offset=0 nr_bits=32 encoding=SIGNED",
+		"[2] PTR '(anon)' type_id=1");
+	split_btf = btf__new_empty_split(base_btf);
+	if (!ASSERT_OK_PTR(split_btf, "empty_split_btf"))
+		goto cleanup;
+	btf__add_struct(split_btf, "s1", 4);			/* [3] struct s1 { */
+	btf__add_field(split_btf, "m", 1, 0, 0);		/*   int m; */
+								/* } */
+	btf__add_struct(split_btf, "s2", 4);			/* [4] struct s2 { */
+	btf__add_field(split_btf, "m", 1, 0, 0);		/*   int m; */
+								/* } */
+	btf__add_func_proto(split_btf, 1);			/* [5] int (*)(int p); */
+	btf__add_func_param(split_btf, "p", 2);
+	btf__add_func(split_btf, "f", BTF_FUNC_STATIC, 5);	/* [6] int f(int *p); */
+
+	VALIDATE_RAW_BTF(
+		split_btf,
+		"[1] INT 'int' size=4 bits_offset=0 nr_bits=32 encoding=SIGNED",
+		"[2] PTR '(anon)' type_id=1",
+		"[3] STRUCT 's1' size=4 vlen=1\n"
+		"\t'm' type_id=1 bits_offset=0",
+		"[4] STRUCT 's2' size=4 vlen=1\n"
+		"\t'm' type_id=1 bits_offset=0",
+		"[5] FUNC_PROTO '(anon)' ret_type_id=1 vlen=1\n"
+		"\t'p' type_id=2",
+		"[6] FUNC 'f' type_id=5 linkage=static");
+
+	permute_ids[0] = 6; /* int f(int *p) */
+	permute_ids[1] = 3; /* struct s1 */
+	permute_ids[2] = 5; /* int (*)(int *p) */
+	permute_ids[3] = 4; /* struct s2 */
+	err = btf__permute(split_btf, permute_ids, NULL);
+	if (!ASSERT_OK(err, "btf__permute"))
+		goto cleanup;
+
+	VALIDATE_RAW_BTF(
+		split_btf,
+		"[1] INT 'int' size=4 bits_offset=0 nr_bits=32 encoding=SIGNED",
+		"[2] PTR '(anon)' type_id=1",
+		"[3] FUNC 'f' type_id=5 linkage=static",
+		"[4] STRUCT 's1' size=4 vlen=1\n"
+		"\t'm' type_id=1 bits_offset=0",
+		"[5] FUNC_PROTO '(anon)' ret_type_id=1 vlen=1\n"
+		"\t'p' type_id=2",
+		"[6] STRUCT 's2' size=4 vlen=1\n"
+		"\t'm' type_id=1 bits_offset=0");
+
+cleanup:
+	btf__free(split_btf);
+	btf__free(base_btf);
+}
+
+void test_btf_permute(void)
+{
+	if (test__start_subtest("permute_base"))
+		test_permute_base();
+	if (test__start_subtest("permute_split"))
+		test_permute_split();
+}
-- 
2.34.1