Add support for dynamically allocating formatted strings through
asprintf() and vasprintf().

Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
---
 tools/include/nolibc/stdio.h                 | 50 ++++++++++++++++++++++++++++
 tools/testing/selftests/nolibc/nolibc-test.c | 24 +++++++++++++
 2 files changed, 74 insertions(+)

diff --git a/tools/include/nolibc/stdio.h b/tools/include/nolibc/stdio.h
index 8f7e1948a651..1c9287b558f0 100644
--- a/tools/include/nolibc/stdio.h
+++ b/tools/include/nolibc/stdio.h
@@ -787,6 +787,56 @@ int sprintf(char *buf, const char *fmt, ...)
 	return ret;
 }
 
+static __attribute__((unused, format(printf, 2, 0)))
+int __nolibc_vasprintf(char **strp, const char *fmt, va_list args1, va_list args2)
+{
+	char *buf;
+	int len;
+
+	len = vsnprintf(NULL, 0, fmt, args1);
+	if (len < 0)
+		return -1;
+
+	buf = malloc(len + 1);
+	if (!buf)
+		return -1;
+
+	len = vsnprintf(buf, len + 1, fmt, args2);
+	if (len < 0) {
+		free(buf);
+		return -1;
+	}
+
+	*strp = buf;
+	return len;
+}
+
+static __attribute__((unused, format(printf, 2, 0)))
+int vasprintf(char **strp, const char *fmt, va_list args)
+{
+	va_list args2;
+	int ret;
+
+	va_copy(args2, args);
+	ret = __nolibc_vasprintf(strp, fmt, args, args2);
+	va_end(args2);
+
+	return ret;
+}
+
+static __attribute__((unused, format(printf, 2, 3)))
+int asprintf(char **strp, const char *fmt, ...)
+{
+	va_list args;
+	int ret;
+
+	va_start(args, fmt);
+	ret = vasprintf(strp, fmt, args);
+	va_end(args);
+
+	return ret;
+}
+
 static __attribute__((unused))
 int vsscanf(const char *str, const char *format, va_list args)
 {
diff --git a/tools/testing/selftests/nolibc/nolibc-test.c b/tools/testing/selftests/nolibc/nolibc-test.c
index c888e13c6bd8..98070b805e49 100644
--- a/tools/testing/selftests/nolibc/nolibc-test.c
+++ b/tools/testing/selftests/nolibc/nolibc-test.c
@@ -1859,6 +1859,29 @@ static int test_printf_error(void)
 	return 0;
 }
 
+int test_asprintf(void)
+{
+	char *str;
+	int ret;
+
+	ret = asprintf(&str, "foo%s", "bar");
+	if (ret == -1)
+		return 1;
+
+	if (ret != 6) {
+		free(str);
+		return 2;
+	}
+
+	if (memcmp(str, "foobar", 6) != 0) {
+		free(str);
+		return 3;
+	}
+
+	free(str);
+	return 0;
+}
+
 static int run_printf(int min, int max)
 {
 	int test;
@@ -1921,6 +1944,7 @@ static int run_printf(int min, int max)
 		CASE_TEST(errno-neg);    errno = -22; EXPECT_VFPRINTF(is_nolibc, "errno=-22   ", "%-12m"); break;
 		CASE_TEST(scanf);        EXPECT_ZR(1, test_scanf()); break;
 		CASE_TEST(printf_error); EXPECT_ZR(1, test_printf_error()); break;
+		CASE_TEST(asprintf);     EXPECT_ZR(1, test_asprintf()); break;
 		case __LINE__:
 			return ret; /* must be last */
 		/* note: do not set any defaults so as to permit holes above */

-- 
2.53.0