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Date: Mon, 20 Mar 2023 01:29:47 +0100
From: Bruno Haible <bruno@...sp.org>
To: musl@...ts.openwall.com
Subject: swprintf: minimum width ignored for %lc
On musl-1.2.3 I see this violation of the POSIX specification of swprintf [1]:
==================================== foo1.c ====================================
#include <stdio.h>
#include <wchar.h>
int main ()
{
static wint_t L_x = (wchar_t) 'x';
wchar_t buf[12] =
{ 0xDEADBEEF, 0xDEADBEEF, 0xDEADBEEF, 0xDEADBEEF, 0xDEADBEEF, 0xDEADBEEF,
0xDEADBEEF, 0xDEADBEEF, 0xDEADBEEF, 0xDEADBEEF, 0xDEADBEEF, 0xDEADBEEF };
int ret = swprintf (buf, 12, L"%10lc", L_x);
printf ("ret = %d, buf[0] = 0x%x, buf[1] = 0x%x, buf[9] = 0x%x, buf[10] = 0x%x, buf[11] = 0x%x\n",
ret,
(unsigned int) buf[0], (unsigned int) buf[1],
(unsigned int) buf[9], (unsigned int) buf[10], (unsigned int) buf[11]);
return 0;
}
/*
glibc: ret = 10, buf[0] = 0x20, buf[1] = 0x20, buf[9] = 0x78, buf[10] = 0x0, buf[11] = 0xdeadbeef
musl libc: ret = 1, buf[0] = 0x78, buf[1] = 0x0, buf[9] = 0xdeadbeef, buf[10] = 0xdeadbeef, buf[11] = 0xdeadbeef
*/
================================================================================
$ gcc -Wall foo1.c
$ ./a.out
ret = 1, buf[0] = 0x78, buf[1] = 0x0, buf[9] = 0xdeadbeef, buf[10] = 0xdeadbeef, buf[11] = 0xdeadbeef
The POSIX specification [1] says:
"An optional minimum field width. If the converted value has fewer wide
characters than the field width, it shall be padded with <space> characters
by default on the left; it shall be padded on the right, if the left-
adjustment flag ( '-' ), described below, is given to the field width. The
field width takes the form of an <asterisk> ( '*' ), described below, or a
decimal integer."
Here, the minimum field width specification of 10 was apparently ignored.
For comparison, in snprintf, this case is handled correctly:
==================================== foo2.c ====================================
#include <stdio.h>
#include <string.h>
#include <wchar.h>
int main ()
{
static wint_t L_x = (wchar_t) 'x';
char buf[12] = { 0xDD, 0xDD, 0xDD, 0xDD, 0xDD, 0xDD, 0xDD, 0xDD, 0xDD, 0xDD, 0xDD, 0xDD };
int ret = snprintf (buf, 12, "%10lc", L_x);
printf ("ret = %d, buf[0] = 0x%x, buf[1] = 0x%x, buf[9] = 0x%x, buf[10] = 0x%x, buf[11] = 0x%x\n",
ret,
(unsigned char) buf[0], (unsigned char) buf[1],
(unsigned char) buf[9], (unsigned char) buf[10], (unsigned char) buf[11]);
return 0;
}
/*
glibc: ret = 10, buf[0] = 0x20, buf[1] = 0x20, buf[9] = 0x78, buf[10] = 0x0, buf[11] = 0xdd
musl libc: ret = 10, buf[0] = 0x20, buf[1] = 0x20, buf[9] = 0x78, buf[10] = 0x0, buf[11] = 0xdd
*/
================================================================================
$ gcc -Wall foo1.c
$ ./a.out
ret = 10, buf[0] = 0x20, buf[1] = 0x20, buf[9] = 0x78, buf[10] = 0x0, buf[11] = 0xdd
Bruno
[1] https://pubs.opengroup.org/onlinepubs/9699919799/functions/swprintf.html
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