Re: [PATCH v4 next 20/23] tools/nolibc/printf: Add support for left aligning fields

[Willy Tarreau]

On Mon, Mar 02, 2026 at 10:18:12AM +0000, david.laight.linux@xxxxxxxxx wrote:
> From: David Laight <david.laight.linux@xxxxxxxxx>
> 
> Output the characters before or after the pad - writing the pad takes more code.
> 
> Include additional/changed tests
> 
> Signed-off-by: David Laight <david.laight.linux@xxxxxxxxx>

Acked-by: Willy Tarreau <w@xxxxxx>

Willy
> ---
> 
> Unchanged for v4.
> 
> Changes for v3:
> - Formally part of patch 7.
> 
>  tools/include/nolibc/stdio.h                 | 6 +++++-
>  tools/testing/selftests/nolibc/nolibc-test.c | 4 +++-
>  2 files changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/include/nolibc/stdio.h b/tools/include/nolibc/stdio.h
> index ef8e7069d5cf..695676b44151 100644
> --- a/tools/include/nolibc/stdio.h
> +++ b/tools/include/nolibc/stdio.h
> @@ -544,7 +544,11 @@ int __nolibc_printf(__nolibc_printf_cb cb, void *state, const char *fmt, va_list
>  		/* Stop gcc back-merging this code into one of the conditionals above. */
>  		_NOLIBC_OPTIMIZER_HIDE_VAR(len);
>  
> +		/* Output the characters on the required side of any padding. */
>  		width -= len;
> +		flags = _NOLIBC_PF_FLAGS_CONTAIN(flags, '-');
> +		if (flags && cb(state, outstr, len) != 0)
> +			return -1;
>  		while (width > 0) {
>  			/* Output pad in 16 byte blocks with the small block first. */
>  			int pad_len = ((width - 1) & 15) + 1;
> @@ -553,7 +557,7 @@ int __nolibc_printf(__nolibc_printf_cb cb, void *state, const char *fmt, va_list
>  			if (cb(state, "                ", pad_len) != 0)
>  				return -1;
>  		}
> -		if (cb(state, outstr, len) != 0)
> +		if (!flags && cb(state, outstr, len) != 0)
>  			return -1;
>  	}
>  
> diff --git a/tools/testing/selftests/nolibc/nolibc-test.c b/tools/testing/selftests/nolibc/nolibc-test.c
> index 4267c69ec37c..89ded1dd7318 100644
> --- a/tools/testing/selftests/nolibc/nolibc-test.c
> +++ b/tools/testing/selftests/nolibc/nolibc-test.c
> @@ -1845,9 +1845,11 @@ static int run_printf(int min, int max)
>  		CASE_TEST(truncation);   EXPECT_VFPRINTF(1, "0123456789012345678901234", "%s", "0123456789012345678901234"); break;
>  		CASE_TEST(string_width); EXPECT_VFPRINTF(1, "         1", "%10s", "1"); break;
>  		CASE_TEST(number_width); EXPECT_VFPRINTF(1, "         1", "%10d", 1); break;
> +		CASE_TEST(number_left);  EXPECT_VFPRINTF(1, "|-5      |", "|%-8d|", -5); break;
> +		CASE_TEST(string_align); EXPECT_VFPRINTF(1, "|foo     |", "|%-8s|", "foo"); break;
>  		CASE_TEST(width_trunc);  EXPECT_VFPRINTF(1, "                        1", "%25d", 1); break;
>  		CASE_TEST(errno);        errno = 22; EXPECT_VFPRINTF(is_nolibc, "errno=22", "%m"); break;
> -		CASE_TEST(errno-neg);    errno = -22; EXPECT_VFPRINTF(is_nolibc, "   errno=-22", "%12m"); break;
> +		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 __LINE__:
> -- 
> 2.39.5