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tools/nolibc: allow limiting of printf destination size

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snprintf() allows limiting the output buffer, while still returning the
number of all bytes that would have been written.
Implement the limitation logic in preparation for snprintf().

Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Acked-by: Willy Tarreau <w@1wt.eu>
This commit is contained in:
Thomas Weißschuh 2025-04-11 11:00:50 +02:00 committed by Thomas Weißschuh
parent f7b3eeffd4
commit 9f4a2e28bc
1 changed files with 10 additions and 6 deletions
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16
tools/include/nolibc/stdio.h
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@ -215,13 +215,13 @@ char *fgets(char *s, int size, FILE *stream)
*/
typedef int (*__nolibc_printf_cb)(intptr_t state, const char *buf, size_t size);
static __attribute__((unused, format(printf, 3, 0)))
int __nolibc_printf(__nolibc_printf_cb cb, intptr_t state, const char *fmt, va_list args)
static __attribute__((unused, format(printf, 4, 0)))
int __nolibc_printf(__nolibc_printf_cb cb, intptr_t state, size_t n, const char *fmt, va_list args)
{
char escape, lpref, c;
unsigned long long v;
unsigned int written;
size_t len, ofs;
size_t len, ofs, w;
char tmpbuf[21];
const char *outstr;
@ -306,8 +306,12 @@ int __nolibc_printf(__nolibc_printf_cb cb, intptr_t state, const char *fmt, va_l
outstr = fmt;
len = ofs - 1;
flush_str:
if (cb(state, outstr, len) != 0)
break;
if (n) {
w = len < n ? len : n;
n -= w;
if (cb(state, outstr, w) != 0)
break;
}
written += len;
do_escape:
@ -331,7 +335,7 @@ static int __nolibc_fprintf_cb(intptr_t state, const char *buf, size_t size)
static __attribute__((unused, format(printf, 2, 0)))
int vfprintf(FILE *stream, const char *fmt, va_list args)
{
return __nolibc_printf(__nolibc_fprintf_cb, (intptr_t)stream, fmt, args);
return __nolibc_printf(__nolibc_fprintf_cb, (intptr_t)stream, SIZE_MAX, fmt, args);
}
static __attribute__((unused, format(printf, 1, 0)))