tools/nolibc/printf: Special case 0 and add support for %#x

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@gmail.com>
Acked-by: Willy Tarreau <w@1wt.eu>
Link: https://patch.msgid.link/20260308113742.12649-14-david.laight.linux@gmail.com
[Thomas: fix up testcases for musl libc]
Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>

2 files changed, 30 insertions, 11 deletions

diff --git a/tools/include/nolibc/stdio.h b/tools/include/nolibc/stdio.h
index 65e113f135d4..db714b1ce274 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.
@@ -471,17 +474,30 @@ 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 = '0' << 8 | 'x';
+					/* "%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 = '0' << 8 | 'x';
+					}
+					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 6fa2346c655a..9644087267d1 100644
--- a/tools/testing/selftests/nolibc/nolibc-test.c
+++ b/tools/testing/selftests/nolibc/nolibc-test.c
@@ -1833,6 +1833,7 @@ 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;
@@ -1840,7 +1841,9 @@ 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(is_nolibc || is_glibc, "(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(is_nolibc || is_glibc, "a%d2", "a%-14l%d%d", 2); break;
 		CASE_TEST(invalid);      EXPECT_VFPRINTF(is_nolibc || is_glibc, "a%12yx3%y42%P", "a%12yx%d%y%d%P", 3, 42); break;