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Date: Mon, 20 Mar 2023 08:18:42 -0400
From: Rich Felker <dalias@libc.org>
To: Bruno Haible <bruno@clisp.org>
Cc: musl@lists.openwall.com
Message-ID: <20230320121841.GR4163@brightrain.aerifal.cx>
References: <11995006.zapYfy813O@nimes>
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User-Agent: Mutt/1.5.21 (2010-09-15)
Subject: Re: [musl] swprintf: minimum width ignored for %lc

On Mon, Mar 20, 2023 at 01:29:47AM +0100, Bruno Haible wrote:
> 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.

Indeed, it's very clear from the code that it was just ignored. This
has a simple direct fix.

Rich