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Message-Id: <20260206191121.3602-8-david.laight.linux@gmail.com>
Date: Fri, 6 Feb 2026 19:11:17 +0000
From: david.laight.linux@...il.com
To: Willy Tarreau <w@....eu>,
Thomas Weißschuh <linux@...ssschuh.net>,
linux-kernel@...r.kernel.org,
Cheng Li <lechain@...il.com>
Cc: David Laight <david.laight.linux@...il.com>
Subject: [PATCH v2 next 07/11] tools/nolibc/printf: Add support for conversion flags "#- +" and format "%X"
From: David Laight <david.laight.linux@...il.com>
Add support for all the normal flag chacacters except '0' (zero pad).
'-' left alignment.
'+' and ' ' Sign characters for non-negative numbers.
'#' adds 0x to hex numbers.
Partially support "%X", outputs lower case a..f the same as "%x".
Move the "%s" code in with the numeric formats to save a va_arg() call.
Prepend the sign (or "0x") after conversion to ascii and use the length
returned by u64toh_r() and u64toa_r().
Both needed for precision and zero-padding in the next patch.
Signed-off-by: David Laight <david.laight.linux@...il.com>
---
Changes for v2:
- Add support for left justifying fields (removed from patch 6).
- Merge in the changes from the old patch 8.
- Add support for "%#x" (formally part of patch 9).
tools/include/nolibc/stdio.h | 97 ++++++++++++++++++++++++++----------
1 file changed, 71 insertions(+), 26 deletions(-)
diff --git a/tools/include/nolibc/stdio.h b/tools/include/nolibc/stdio.h
index b14cf8224403..032416e900ee 100644
--- a/tools/include/nolibc/stdio.h
+++ b/tools/include/nolibc/stdio.h
@@ -240,10 +240,16 @@ char *fgets(char *s, int size, FILE *stream)
}
-/* simple printf(). It supports the following formats:
- * - %[-][width][{l,t,z,ll,L,j,q}]{d,u,c,x,p,s,m,%}
- * - %%
- * - invalid formats are copied to the output buffer
+/* printf(). Supports most of the normal integer and string formats.
+ * - %[#-+ ][width][{l,t,z,ll,L,j,q}]{d,i,u,c,x,X,p,s,m,%}
+ * - %% generates a single %
+ * - %m outputs strerror(errno).
+ * - # only affects %x and prepends 0x to non-zero values.
+ * - %o (octal) isn't supported.
+ * - %X outputs a..f the same as %x.
+ * - No support for zero padding, precision or variable widths.
+ * - No support for wide characters.
+ * - invalid formats are copied to the output buffer.
*/
/* This code uses 'flag' variables that are indexed by the low 6 bits
@@ -279,7 +285,7 @@ int __nolibc_printf(__nolibc_printf_cb cb, void *state, const char *fmt, va_list
unsigned int written, width;
unsigned int flags, ch_flag;
size_t len;
- char tmpbuf[21];
+ char tmpbuf[32 + 24];
const char *outstr;
written = 0;
@@ -334,19 +340,32 @@ int __nolibc_printf(__nolibc_printf_cb cb, void *state, const char *fmt, va_list
/* Conversion specifiers. */
- /* Numeric conversion specifiers. */
- ch_flag = _NOLIBC_PF_CHAR_IS_ONE_OF(ch, 'c', 'd', 'i', 'u', 'x', 'p');
- if (ch_flag != 0) {
+ /* Numeric and pointer conversion specifiers.
+ *
+ * Use an explicit bound check (rather than _NOLIBC_PF_CHAR_IS_ONE_OF())
+ * so that 'X' can be allowed through.
+ * 'X' gets treated and 'x' because _NOLIBC_PF_FLAG() returns the same
+ * value for both.
+ */
+ if ((ch < 'a' || ch > 'z') && ch != 'X')
+ goto non_numeric_conversion;
+
+ /* 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) | (flags & _NOLIBC_PF_FLAG('#')) >> 1;
+ if (_NOLIBC_PF_FLAGS_CONTAIN(ch_flag, 'c', 'd', 'i', 'u', 'x', 'p', 's')) {
unsigned long long v;
long long signed_v;
- char *out = tmpbuf;
+ char *out = tmpbuf + 32;
+ int sign = 0;
/* 'long' is needed for pointer/string conversions and ltz lengths.
* A single test can be used provided 'p' (the same bit as '0')
* is masked from flags.
*/
if (_NOLIBC_PF_FLAGS_CONTAIN(ch_flag | (flags & ~_NOLIBC_PF_FLAG('p')),
- 'p', 'l', 't', 'z')) {
+ 'p', 's', 'l', 't', 'z')) {
v = va_arg(args, unsigned long);
signed_v = (long)v;
} else if (_NOLIBC_PF_FLAGS_CONTAIN(flags, 'j', 'q')) {
@@ -365,40 +384,62 @@ int __nolibc_printf(__nolibc_printf_cb cb, void *state, const char *fmt, va_list
goto do_output;
}
+ if (_NOLIBC_PF_FLAGS_CONTAIN(ch_flag, 's')) {
+ /* "%s" - character string. */
+ if (!v) {
+ outstr = "(null)";
+ len = 6;
+ goto do_output;
+ }
+ outstr = (void *)v;
+do_strnlen_output:
+ len = strnlen(outstr, INT_MAX);
+ goto do_output;
+ }
+
if (_NOLIBC_PF_FLAGS_CONTAIN(ch_flag, 'd', 'i')) {
/* "%d" and "%i" - signed decimal numbers. */
if (signed_v < 0) {
- *out++ = '-';
+ sign = '-';
v = -(signed_v + 1);
v++;
+ } else if (_NOLIBC_PF_FLAGS_CONTAIN(flags, '+')) {
+ sign = '+';
+ } else if (_NOLIBC_PF_FLAGS_CONTAIN(flags, ' ')) {
+ sign = ' ';
}
}
/* Convert the number to ascii in the required base. */
if (_NOLIBC_PF_FLAGS_CONTAIN(ch_flag, 'd', 'i', 'u')) {
/* Base 10 */
- u64toa_r(v, out);
+ len = u64toa_r(v, out);
} else {
/* Base 16 */
- if (_NOLIBC_PF_FLAGS_CONTAIN(ch_flag, 'p')) {
- *(out++) = '0';
- *(out++) = 'x';
+ if (_NOLIBC_PF_FLAGS_CONTAIN(ch_flag, 'p', '#' - 1)) {
+ /* "%p" and "%#x" need "0x" prepending. */
+ sign = 'x' | '0' << 8;
}
- u64toh_r(v, out);
+ len = u64toh_r(v, out);
}
- outstr = tmpbuf;
- }
- else if (ch == 's') {
- outstr = va_arg(args, char *);
- if (!outstr)
- outstr="(null)";
+ /* Add 0, 1 or 2 ("0x") sign characters left of any zero padding */
+ for (; sign; sign >>= 8) {
+ len++;
+ *--out = sign;
+ }
+ outstr = out;
+ goto do_output;
}
- else if (ch == 'm') {
+
+non_numeric_conversion:
+ if (ch == 'm') {
#ifdef NOLIBC_IGNORE_ERRNO
outstr = "unknown error";
+ len = __builtin_strlen(outstr);
#else
outstr = strerror(errno);
+ goto do_strnlen_output;
#endif /* NOLIBC_IGNORE_ERRNO */
} else {
if (ch != '%') {
@@ -409,10 +450,10 @@ int __nolibc_printf(__nolibc_printf_cb cb, void *state, const char *fmt, va_list
/* %% is documented as a 'conversion specifier'.
* Any flags, precision or length modifier are ignored.
*/
+ len = 1;
width = 0;
- outstr = "%";
+ outstr = fmt - 1;
}
- len = strlen(outstr);
}
do_output:
@@ -423,6 +464,10 @@ int __nolibc_printf(__nolibc_printf_cb cb, void *state, const char *fmt, va_list
*/
__asm__ volatile("" : "=r"(len) : "0"(len));
+ /* Output 'left pad', 'value' then 'right pad'. */
+ flags = _NOLIBC_PF_FLAGS_CONTAIN(flags, '-');
+ if (flags && cb(state, outstr, len) != 0)
+ return -1;
while (width > len) {
unsigned int pad_len = ((width - len - 1) & 15) + 1;
width -= pad_len;
@@ -430,7 +475,7 @@ 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;
}
--
2.39.5
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