linux-kernel - [PATCH 1/2] tools/nolibc: add support zero pad (0) in printf

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Message-ID: <20260130083737.1123-1-im.lechain@gmail.com>
Date: Fri, 30 Jan 2026 16:37:35 +0800
From: "licheng.li" <im.lechain@...il.com>
To: Willy Tarreau <w@....eu>,
	David Laight <david.laight.linux@...il.com>
Cc: Thomas Weißschuh <linux@...ssschuh.net>,
	linux-kernel@...r.kernel.org,
	im.lechain@...il.com
Subject: [PATCH 1/2] tools/nolibc: add support zero pad (0) in printf

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

This patch correctly implements the '0' flag in __nolibc_printf() to
allow zero-padding for numeric and pointer outputs.

Thanks to David for pointing out the errors in the previous implementation.

The logic ensures that the sign ('-') for negative numbers or the prefix
('0x') for pointers is printed before the padding zeros, adhering to
standard printf behavior (e.g., producing "-0005" instead of "000-5").

Examples of the corrected padding logic:
 - ("%05d", -5)  -> "-0005"
 - ("%05p", ptr)  -> "0x00..."

Signed-off-by: Cheng Li <im.lechain@...il.com>
---
 tools/include/nolibc/stdio.h | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/tools/include/nolibc/stdio.h b/tools/include/nolibc/stdio.h
index f31b77f61d3b..8a4af259a31b 100644
--- a/tools/include/nolibc/stdio.h
+++ b/tools/include/nolibc/stdio.h
@@ -267,7 +267,7 @@ int __nolibc_printf(__nolibc_printf_cb cb, intptr_t state, size_t n, const char
 			/* we're in an escape sequence, ofs == 1 */
 			escape = 0;
 
-			if (c == '-') {
+			if (c == '-' || c == '0') {
 				padc = c;
 				c = fmt[ofs++];
 			}
@@ -364,9 +364,21 @@ int __nolibc_printf(__nolibc_printf_cb cb, intptr_t state, size_t n, const char
 			if (n) {
 				w = len < n ? len : n;
 				n -= w;
+				if (padc == '0') {
+					if (outstr[0] == '-') {
+						if (cb(state, outstr, 1) != 0)
+							return -1;
+						outstr++;
+					}
+					if (outstr[0] == '0' && outstr[1] == 'x') {
+						if (cb(state, outstr, 2) != 0)
+							return -1;
+						outstr += 2;
+					}
+				}
 				while (width > w && padc != '-') {
 					written += 1;
-					if (cb(state, " ", 1) != 0)
+					if (cb(state, &padc, 1) != 0)
 						return -1;
 					width--;
 				}
-- 
2.52.0