[PATCH v4 next 19/23] tools/nolibc/printf: Special case 0 and add support for %#x
From: david . laight . linux
Date: Mon Mar 02 2026 - 05:28:15 EST
From: David Laight <david.laight.linux@xxxxxxxxx>
The output for %#x is almost the same as that for %p, both output in
hexadecimal with a leading "0x".
However for zero %#x should just output "0" (the same as decimal and ocal).
For %p match glibc and output "(nil)" rather than "0x0" or "0".
Add tests for "%#x", "% d", "%+d" and passing NULL to "%p".
Signed-off-by: David Laight <david.laight.linux@xxxxxxxxx>
---
v4: Split into its' own patch.
tools/include/nolibc/stdio.h | 38 ++++++++++++++------
tools/testing/selftests/nolibc/nolibc-test.c | 3 ++
2 files changed, 30 insertions(+), 11 deletions(-)
diff --git a/tools/include/nolibc/stdio.h b/tools/include/nolibc/stdio.h
index 5d75e8530ce2..ef8e7069d5cf 100644
--- a/tools/include/nolibc/stdio.h
+++ b/tools/include/nolibc/stdio.h
@@ -296,7 +296,7 @@ int fseek(FILE *stream, long offset, int whence)
* - %% generates a single %
* - %m outputs strerror(errno).
* - %X outputs a..f the same as %x.
- * - The modifiers [#-0] are currently ignored.
+ * - The modifiers [-0] are currently ignored.
* - No support for precision or variable widths.
* - No support for floating point or wide characters.
* - Invalid formats are copied to the output buffer.
@@ -410,8 +410,11 @@ int __nolibc_printf(__nolibc_printf_cb cb, void *state, const char *fmt, va_list
* so that 'X' can be allowed through.
* 'X' gets treated and 'x' because _NOLIBC_PF_FLAG() returns the same
* value for both.
+ *
+ * We need to check for "%p" or "%#x" later, merging here gives better code.
+ * But '#' collides with 'c' so shift right.
*/
- ch_flag = _NOLIBC_PF_FLAG(ch);
+ ch_flag = _NOLIBC_PF_FLAG(ch) | (flags & _NOLIBC_PF_FLAG('#')) >> 1;
if (((ch >= 'a' && ch <= 'z') || ch == 'X') &&
_NOLIBC_PF_FLAGS_CONTAIN(ch_flag, 'c', 'd', 'i', 'u', 'x', 'p', 's')) {
/* 'long' is needed for pointer/string conversions and ltz lengths.
@@ -470,17 +473,30 @@ int __nolibc_printf(__nolibc_printf_cb cb, void *state, const char *fmt, va_list
*/
out = outbuf + 2;
- /* Convert the number to ascii in the required base. */
- if (_NOLIBC_PF_FLAGS_CONTAIN(ch_flag, 'd', 'i', 'u')) {
- /* Base 10 */
- len = u64toa_r(v, out);
- } else {
- /* Base 16 */
+ if (v == 0) {
+ /* There are special rules for zero. */
if (_NOLIBC_PF_FLAGS_CONTAIN(ch_flag, 'p')) {
- /* "%p" needs "0x" prepending. */
- sign_prefix = 'x' | '0' << 8;
+ /* "%p" match glibc, precision is ignored */
+ outstr = "(nil)";
+ len = 5;
+ goto do_output;
+ }
+ /* All other formats (including "%#x") just output "0". */
+ out[0] = '0';
+ len = 1;
+ } else {
+ /* Convert the number to ascii in the required base. */
+ if (_NOLIBC_PF_FLAGS_CONTAIN(ch_flag, 'd', 'i', 'u')) {
+ /* Base 10 */
+ len = u64toa_r(v, out);
+ } else {
+ /* Base 16 */
+ if (_NOLIBC_PF_FLAGS_CONTAIN(ch_flag, 'p', '#' - 1)) {
+ /* "%p" and "%#x" need "0x" prepending. */
+ sign_prefix = 'x' | '0' << 8;
+ }
+ len = u64toh_r(v, out);
}
- len = u64toh_r(v, out);
}
/* Add the 0, 1 or 2 ("0x") sign/prefix characters at the front. */
diff --git a/tools/testing/selftests/nolibc/nolibc-test.c b/tools/testing/selftests/nolibc/nolibc-test.c
index a140c54e4d72..4267c69ec37c 100644
--- a/tools/testing/selftests/nolibc/nolibc-test.c
+++ b/tools/testing/selftests/nolibc/nolibc-test.c
@@ -1825,6 +1825,7 @@ static int run_printf(int min, int max)
CASE_TEST(string); EXPECT_VFPRINTF(1, "foo", "%s", "foo"); break;
CASE_TEST(number); EXPECT_VFPRINTF(1, "1234", "%d", 1234); break;
CASE_TEST(negnumber); EXPECT_VFPRINTF(1, "-1234", "%d", -1234); break;
+ CASE_TEST(num_sign); EXPECT_VFPRINTF(1, "| 1|+2|+3|+4|5|", "|% d|%+d|% +d|%+ d|%#d|", 1, 2, 3, 4, 5); break;
CASE_TEST(unsigned); EXPECT_VFPRINTF(1, "12345", "%u", 12345); break;
CASE_TEST(signed_max); EXPECT_VFPRINTF(1, "2147483647", "%i", ~0u >> 1); break;
CASE_TEST(signed_min); EXPECT_VFPRINTF(1, "-2147483648", "%i", (~0u >> 1) + 1); break;
@@ -1832,7 +1833,9 @@ static int run_printf(int min, int max)
CASE_TEST(char); EXPECT_VFPRINTF(1, "c", "%c", 'c'); break;
CASE_TEST(hex_nolibc); EXPECT_VFPRINTF(is_nolibc, "|f|d|", "|%x|%X|", 0xf, 0xd); break;
CASE_TEST(hex_libc); EXPECT_VFPRINTF(!is_nolibc, "|f|D|", "|%x|%X|", 0xf, 0xd); break;
+ CASE_TEST(hex_alt); EXPECT_VFPRINTF(1, "|0x1| 0x2| 0|", "|%#x|%#5x|%#5x|", 1, 2, 0); break;
CASE_TEST(pointer); EXPECT_VFPRINTF(1, "0x1", "%p", (void *) 0x1); break;
+ CASE_TEST(pointer_NULL); EXPECT_VFPRINTF(1, "(nil)", "%p", (void *)0); break;
CASE_TEST(percent); EXPECT_VFPRINTF(1, "a%d42%69%", "a%%d%d%%%d%%", 42, 69); break;
CASE_TEST(perc_qual); EXPECT_VFPRINTF(1, "a%d2", "a%-14l%d%d", 2); break;
CASE_TEST(invalid); EXPECT_VFPRINTF(1, "a%12yx3%y42%P", "a%12yx%d%y%d%P", 3, 42); break;
--
2.39.5