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

From: david . laight . linux

Date: Mon Mar 02 2026 - 05:26:55 EST


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>
---

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