selftest/bpf: Extend the bpf_snprintf() test for "%c".

This patch adds various "positive" patterns for "%c" and two "negative"
patterns for wide character.
Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.co.jp>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20210814015718.42704-5-kuniyu@amazon.co.jp

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  b c      d e 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");
 }

tools/testing/selftests/bpf/progs/test_snprintf.c

@@ -59,9 +59,9 @@ 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 %+2c %-3c %04c %0c %+05s",
+				str1, 'a', 'b', 'c', 'd', 'e', longstr);
 	/* Overflow */
 	over_ret = BPF_SNPRINTF(over_out, sizeof(over_out), "%%overflow");
 	/* Padding of fixed width numbers */