linux-kernel - [PATCH 1/2] tools/nolibc: support left-aligned printing in printf

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-ID: <20260126031038.35387-1-im.lechain@gmail.com>
Date: Mon, 26 Jan 2026 11:10:37 +0800
From: "licheng.li" <im.lechain@...il.com>
To: Willy Tarreau <w@....eu>
Cc: Thomas Weißschuh <linux@...ssschuh.net>,
	linux-kernel@...r.kernel.org,
	im.lechain@...il.com
Subject: [PATCH 1/2] tools/nolibc: support left-aligned printing in printf

From: Cheng Li <im.lechain@...il.com>

Currently, __nolibc_printf() in nolibc does not support the '-' flag
for left alignment. This limits the ability to format tabular output
nicely.

This patch adds support for the '-' flag. The implementation is kept
minimal to minimize the binary size impact.

Measuring the nolibc-test binary on x86_64 shows a small increase in
the text section:

  text    data     bss     dec     hex filename
 43552     248     112   43912    ab88 nolibc-test (before)
 43677     248     112   44037    ac05 nolibc-test (after)

The net increase is 125 bytes.

Signed-off-by: Cheng Li <im.lechain@...il.com>
---
 tools/include/nolibc/stdio.h | 18 +++++++++++++++---
 1 file changed, 15 insertions(+), 3 deletions(-)

diff --git a/tools/include/nolibc/stdio.h b/tools/include/nolibc/stdio.h
index 1f16dab2ac88..b90b59237bda 100644
--- a/tools/include/nolibc/stdio.h
+++ b/tools/include/nolibc/stdio.h
@@ -250,7 +250,7 @@ typedef int (*__nolibc_printf_cb)(intptr_t state, const char *buf, size_t size);
 static __attribute__((unused, format(printf, 4, 0)))
 int __nolibc_printf(__nolibc_printf_cb cb, intptr_t state, size_t n, const char *fmt, va_list args)
 {
-	char escape, lpref, c;
+	char escape, lpref, padc, c;
 	unsigned long long v;
 	unsigned int written, width;
 	size_t len, ofs, w;
@@ -261,11 +261,17 @@ int __nolibc_printf(__nolibc_printf_cb cb, intptr_t state, size_t n, const char
 	while (1) {
 		c = fmt[ofs++];
 		width = 0;
+		padc = ' ';
 
 		if (escape) {
 			/* we're in an escape sequence, ofs == 1 */
 			escape = 0;
 
+			if (c == '-' || c == '0') {
+				padc = c;
+				c = fmt[ofs++];
+			}
+
 			/* width */
 			while (c >= '0' && c <= '9') {
 				width *= 10;
@@ -358,13 +364,19 @@ int __nolibc_printf(__nolibc_printf_cb cb, intptr_t state, size_t n, const char
 			if (n) {
 				w = len < n ? len : n;
 				n -= w;
-				while (width-- > w) {
-					if (cb(state, " ", 1) != 0)
+				while (padc != '-' && width > w) {
+					if (cb(state, &padc, 1) != 0)
 						return -1;
 					written += 1;
+					width--;
 				}
 				if (cb(state, outstr, w) != 0)
 					return -1;
+				while (width-- > w) {
+					if (cb(state, " ", 1) != 0)
+						return -1;
+					written += 1;
+				}
 			}
 
 			written += len;
-- 
2.52.0