[PATCH] selftests/bpf: improve test coverage for kfunc call

[Hari Bathini <hbathini@linux.ibm.com>]

On powerpc, immediate load instructions are sign extended. In case
of unsigned types, arguments should be explicitly zero-extended by
the caller. For kfunc call, this needs to be handled in the JIT code.
While kfunc_call_test4 test case already checks for sign-extension of
signed argument types in kfunc calls, zero-extension for unsigned
argument types is being checked with this test case.

Signed-off-by: Hari Bathini <hbathini@linux.ibm.com>
---

- powerpc BPF JIT was not handling ABI sign-extension & zero-extension
  appropriately for kfunc calls. Fixed with:

    https://lore.kernel.org/all/20260303130208.325249-7-hbathini@linux.ibm.com/


 .../selftests/bpf/prog_tests/kfunc_call.c     |  1 +
 .../selftests/bpf/progs/kfunc_call_test.c     | 34 +++++++++++++++++++
 .../selftests/bpf/test_kmods/bpf_testmod.c    | 28 +++++++++++++++
 .../bpf/test_kmods/bpf_testmod_kfunc.h        |  1 +
 4 files changed, 64 insertions(+)

diff --git a/tools/testing/selftests/bpf/prog_tests/kfunc_call.c b/tools/testing/selftests/bpf/prog_tests/kfunc_call.c
index f79c8e53cb3e..fb06f2485197 100644
--- a/tools/testing/selftests/bpf/prog_tests/kfunc_call.c
+++ b/tools/testing/selftests/bpf/prog_tests/kfunc_call.c
@@ -74,6 +74,7 @@ static struct kfunc_test_params kfunc_tests[] = {
 	TC_TEST(kfunc_call_test1, 12),
 	TC_TEST(kfunc_call_test2, 3),
 	TC_TEST(kfunc_call_test4, -1234),
+	TC_TEST(kfunc_call_test5, 0),
 	TC_TEST(kfunc_call_test_ref_btf_id, 0),
 	TC_TEST(kfunc_call_test_get_mem, 42),
 	SYSCALL_TEST(kfunc_syscall_test, 0),
diff --git a/tools/testing/selftests/bpf/progs/kfunc_call_test.c b/tools/testing/selftests/bpf/progs/kfunc_call_test.c
index 8b86113a0126..a32c3a60fa4f 100644
--- a/tools/testing/selftests/bpf/progs/kfunc_call_test.c
+++ b/tools/testing/selftests/bpf/progs/kfunc_call_test.c
@@ -4,6 +4,40 @@
 #include <bpf/bpf_helpers.h>
 #include "../test_kmods/bpf_testmod_kfunc.h"
 
+SEC("tc")
+int kfunc_call_test5(struct __sk_buff *skb)
+{
+	struct bpf_sock *sk = skb->sk;
+	int ret;
+	u32 val32;
+	u16 val16;
+	u8 val8;
+
+	if (!sk)
+		return -1;
+
+	sk = bpf_sk_fullsock(sk);
+	if (!sk)
+		return -1;
+
+	ret = bpf_kfunc_call_test5(0xFF, 0xFFFF, 0xFFFFFFFF);
+	if (ret)
+		return ret;
+
+	val32 = bpf_get_prandom_u32();
+	val16 = val32 & 0xFFFF;
+	val8 = val32 & 0xFF;
+	ret = bpf_kfunc_call_test5(val8, val16, val32);
+	if (ret)
+		return ret;
+
+	ret = bpf_kfunc_call_test5(val8 * 0xFF, val16 * 0xFFFF, val32 * 0xFFFFFFFF);
+	if (ret)
+		return ret;
+
+	return 0;
+}
+
 SEC("tc")
 int kfunc_call_test4(struct __sk_buff *skb)
 {
diff --git a/tools/testing/selftests/bpf/test_kmods/bpf_testmod.c b/tools/testing/selftests/bpf/test_kmods/bpf_testmod.c
index e62c6b78657f..de4897ddcff1 100644
--- a/tools/testing/selftests/bpf/test_kmods/bpf_testmod.c
+++ b/tools/testing/selftests/bpf/test_kmods/bpf_testmod.c
@@ -766,6 +766,33 @@ __bpf_kfunc long noinline bpf_kfunc_call_test4(signed char a, short b, int c, lo
 	return (long)a + (long)b + (long)c + d;
 }
 
+__bpf_kfunc int bpf_kfunc_call_test5(u8 a, u16 b, u32 c)
+{
+	/* Make val as volatile to avoid compiler optimizations on the below checks */
+	volatile long val = a;
+
+	/* Check zero-extension */
+	if (val != (unsigned long)a)
+		return 1;
+	/* Check no sign-extension */
+	if (val < 0)
+		return 2;
+
+	val = b;
+	if (val != (unsigned long)b)
+		return 3;
+	if (val < 0)
+		return 4;
+
+	val = c;
+	if (val != (unsigned long)c)
+		return 5;
+	if (val < 0)
+		return 6;
+
+	return 0;
+}
+
 static struct prog_test_ref_kfunc prog_test_struct = {
 	.a = 42,
 	.b = 108,
@@ -1228,6 +1255,7 @@ BTF_ID_FLAGS(func, bpf_kfunc_call_test1)
 BTF_ID_FLAGS(func, bpf_kfunc_call_test2)
 BTF_ID_FLAGS(func, bpf_kfunc_call_test3)
 BTF_ID_FLAGS(func, bpf_kfunc_call_test4)
+BTF_ID_FLAGS(func, bpf_kfunc_call_test5)
 BTF_ID_FLAGS(func, bpf_kfunc_call_test_mem_len_pass1)
 BTF_ID_FLAGS(func, bpf_kfunc_call_test_mem_len_fail1)
 BTF_ID_FLAGS(func, bpf_kfunc_call_test_mem_len_fail2)
diff --git a/tools/testing/selftests/bpf/test_kmods/bpf_testmod_kfunc.h b/tools/testing/selftests/bpf/test_kmods/bpf_testmod_kfunc.h
index b393bf771131..aa0b8d41e71b 100644
--- a/tools/testing/selftests/bpf/test_kmods/bpf_testmod_kfunc.h
+++ b/tools/testing/selftests/bpf/test_kmods/bpf_testmod_kfunc.h
@@ -110,6 +110,7 @@ __u64 bpf_kfunc_call_test1(struct sock *sk, __u32 a, __u64 b,
 int bpf_kfunc_call_test2(struct sock *sk, __u32 a, __u32 b) __ksym;
 struct sock *bpf_kfunc_call_test3(struct sock *sk) __ksym;
 long bpf_kfunc_call_test4(signed char a, short b, int c, long d) __ksym;
+int bpf_kfunc_call_test5(__u8 a, __u16 b, __u32 c) __ksym;
 
 void bpf_kfunc_call_test_pass_ctx(struct __sk_buff *skb) __ksym;
 void bpf_kfunc_call_test_pass1(struct prog_test_pass1 *p) __ksym;
-- 
2.53.0