Re: [PATCH 2/3] tools/nolibc: fix fopen() with the "rb+", "wb+" and "ab+" modes

[Thomas Weißschuh]

On 2026-10-28 15:07:42-0500, Danish Khateeb wrote:
> The C standard allows the '+' of an update mode to come before or after
> the 'b', so "rb+" means the same as "r+b". fopen() only looks for the
> '+' right after the first character, so it opens a file read-only in
> "rb+" mode, and write-only in "wb+" and "ab+" modes. Writing to such a
> stream, or reading from it, then fails with EBADF.
> 
> Look for the '+' anywhere in the mode string.
> 
> Fixes: a009a0c6faa9 ("tools/nolibc: add fopen()")

The original implementation explicitly does not support 'b'.
I guess we can add support for it, but then the Fixes is misplaced
and the message needs to be reworded.

> Signed-off-by: Danish Khateeb <danishkhateeb03@xxxxxxxxx>
> ---
>  tools/include/nolibc/stdio.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/tools/include/nolibc/stdio.h b/tools/include/nolibc/stdio.h
> index 00a95a267d90..205b06f18b4b 100644
> --- a/tools/include/nolibc/stdio.h
> +++ b/tools/include/nolibc/stdio.h
> @@ -75,7 +75,7 @@ FILE *fopen(const char *pathname, const char *mode)
>  		SET_ERRNO(EINVAL); return NULL;
>  	}
>  
> -	if (mode[1] == '+')
> +	if (strchr(mode, '+'))
>  		flags = (flags & ~(O_RDONLY | O_WRONLY)) | O_RDWR;
>  
>  	fd = open(pathname, flags, 0666);
> -- 
> 2.56.0
>