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

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Message-ID: <222455c7-17a8-4b1f-a574-4e945467eb12@weissschuh.net>
Date: Sat, 31 Jan 2026 11:18:49 +0100
From: Thomas Weißschuh <linux@...ssschuh.net>
To: "licheng.li" <im.lechain@...il.com>
Cc: Willy Tarreau <w@....eu>, David Laight <david.laight.linux@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] tools/nolibc: add support zero pad (0) in printf

Hey Cheng,

Jan 30, 2026 09:37:51 licheng.li <im.lechain@...il.com>:

> 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 for (all of) your patches.
I am not sure when exactly I can take a proper look at them.
As we are currently fairly late in the 6.20/7.0 development cycle I would like move your patches into the next one.
We can still discuss the patches and you can send new revisions and patches,
but they won't be picked up until in a few weeks.

> 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