[26/32] tools/nolibc: allow limiting of printf destination size

Commit Message

Thomas Weißschuh March 4, 2025, 7:10 a.m. UTC

snprintf() allows limiting the output buffer, while still returning the
number of all bytes that would have been written.
Implement the limitation logic in preparation for snprintf().

Signed-off-by: Thomas Weißschuh <[e-mail]>
---
 tools/include/nolibc/stdio.h | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

Patch

diff --git a/tools/include/nolibc/stdio.h b/tools/include/nolibc/stdio.h
index 434fbaddae7a216159fecf618da85889d631dff7..b484a19466394d55d7d21248031837238b58f3ff 100644
--- a/tools/include/nolibc/stdio.h
+++ b/tools/include/nolibc/stdio.h
@@ -215,13 +215,13 @@  char *fgets(char *s, int size, FILE *stream)
  */
 typedef int (*_printf_cb)(intptr_t state, const char *buf, size_t size);
 
-static __attribute__((unused, format(printf, 3, 0)))
-int _printf(_printf_cb cb, intptr_t state, const char *fmt, va_list args)
+static __attribute__((unused, format(printf, 4, 0)))
+int _printf(_printf_cb cb, intptr_t state, size_t n, const char *fmt, va_list args)
 {
 	char escape, lpref, c;
 	unsigned long long v;
 	unsigned int written;
-	size_t len, ofs;
+	size_t len, ofs, w;
 	char tmpbuf[21];
 	const char *outstr;
 
@@ -306,8 +306,12 @@  int _printf(_printf_cb cb, intptr_t state, const char *fmt, va_list args)
 			outstr = fmt;
 			len = ofs - 1;
 		flush_str:
-			if (cb(state, outstr, len) != 0)
-				break;
+			if (n) {
+				w = len < n ? len : n;
+				n -= w;
+				if (cb(state, outstr, w) != 0)
+					break;
+			}
 
 			written += len;
 		do_escape:
@@ -331,7 +335,7 @@  static int _fprintf_cb(intptr_t state, const char *buf, size_t size)
 static __attribute__((unused, format(printf, 2, 0)))
 int vfprintf(FILE *stream, const char *fmt, va_list args)
 {
-	return _printf(_fprintf_cb, (intptr_t)stream, fmt, args);
+	return _printf(_fprintf_cb, (intptr_t)stream, SIZE_MAX, fmt, args);
 }
 
 static __attribute__((unused, format(printf, 1, 0)))