This patch adds a "positive" pattern for "%c", which intentionally uses a
__u32 value (0x64636261, "dbca") to print a single character "a".  If the
implementation went wrong, other 3 bytes might show up as the part of the
latter "%+05s".

Also, this patch adds two "negative" patterns for wide character.

Signed-off-by: Kuniyuki Iwashima <redacted>
---
 tools/testing/selftests/bpf/prog_tests/snprintf.c | 4 +++-
 tools/testing/selftests/bpf/progs/test_snprintf.c | 7 ++++---
 2 files changed, 7 insertions(+), 4 deletions(-)

diff --git a/tools/testing/selftests/bpf/prog_tests/snprintf.c b/tools/testing/selftests/bpf/prog_tests/snprintf.c
index dffbcaa1ec98..f77d7def7fed 100644
--- a/tools/testing/selftests/bpf/prog_tests/snprintf.c
+++ b/tools/testing/selftests/bpf/prog_tests/snprintf.c

@@ -19,7 +19,7 @@
 #define EXP_ADDR_OUT "0000000000000000 ffff00000add4e55 "
 #define EXP_ADDR_RET sizeof(EXP_ADDR_OUT "unknownhashedptr")

-#define EXP_STR_OUT  "str1 longstr"
+#define EXP_STR_OUT  "str1         a longstr"
 #define EXP_STR_RET  sizeof(EXP_STR_OUT)

 #define EXP_OVER_OUT "%over"

@@ -114,6 +114,8 @@ void test_snprintf_negative(void)
        ASSERT_ERR(load_single_snprintf("%"), "invalid specifier 3");
        ASSERT_ERR(load_single_snprintf("%12345678"), "invalid specifier 4");
        ASSERT_ERR(load_single_snprintf("%--------"), "invalid specifier 5");
+       ASSERT_ERR(load_single_snprintf("%lc"), "invalid specifier 6");
+       ASSERT_ERR(load_single_snprintf("%llc"), "invalid specifier 7");
        ASSERT_ERR(load_single_snprintf("\x80"), "non ascii character");
        ASSERT_ERR(load_single_snprintf("\x1"), "non printable character");
 }

diff --git a/tools/testing/selftests/bpf/progs/test_snprintf.c b/tools/testing/selftests/bpf/progs/test_snprintf.c
index e2ad26150f9b..afc2c583125b 100644
--- a/tools/testing/selftests/bpf/progs/test_snprintf.c
+++ b/tools/testing/selftests/bpf/progs/test_snprintf.c

@@ -40,6 +40,7 @@ int handler(const void *ctx)
        /* Convenient values to pretty-print */
        const __u8 ex_ipv4[] = {127, 0, 0, 1};
        const __u8 ex_ipv6[] = {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1};
+       const __u32 chr1 = 0x64636261; /* dcba */
        static const char str1[] = "str1";
        static const char longstr[] = "longstr";

@@ -59,9 +60,9 @@ int handler(const void *ctx)
        /* Kernel pointers */
        addr_ret = BPF_SNPRINTF(addr_out, sizeof(addr_out), "%pK %px %p",
                                0, 0xFFFF00000ADD4E55, 0xFFFF00000ADD4E55);
-       /* Strings embedding */
-       str_ret  = BPF_SNPRINTF(str_out, sizeof(str_out), "%s %+05s",
-                               str1, longstr);
+       /* Strings and single-byte character embedding */
+       str_ret  = BPF_SNPRINTF(str_out, sizeof(str_out), "%s % 9c %+05s",
+                               str1, chr1, longstr);