Re: [Minios-devel] [UNIKRAFT PATCH v2] lib/nolibc: Fix vsnprintf when size is zero

[Florian Schmidt <Florian.Schmidt@xxxxxxxxx>]

Hi Razvan,

thank you for the update! Patch looks good:

Reviewed-by: Florian Schmidt <florian.schmidt@xxxxxxxxx>

As discussed off-list, I will update the commit message slightly to 
clarify and then push this in a bit.
Cheers,
Florian

On 08/21/2018 01:21 PM, Razvan Rotaru wrote:
> Modified PCHAR macro so that it evaluates it's params and updates their values 
> every time.
> As vsnprintf is firstly called to compute the length of the resulting
> string with a size equal to zero given as parameter, the PCHAR
> macro will not evaluate its decrementing argument since the internal condition 
> needs
> the size to be greater than two to compute the decrement. Cases like this lead
> to infinite loops. To solve this issue a new variable is used before the if 
> statement,
> forcing any modification to occur.
> ---
>   lib/nolibc/stdio.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/lib/nolibc/stdio.c b/lib/nolibc/stdio.c
> index 7e3d368..d2637ee 100644
> --- a/lib/nolibc/stdio.c
> +++ b/lib/nolibc/stdio.c
> @@ -101,8 +101,9 @@ int vsnprintf(char *str, size_t size, const char *fmt, 
> va_list ap)
>   {
>   #define PCHAR(c)                                                              
>  \
>         {                                                                      \
> +               int cc = (c);                                                  \
>                 if (size >= 2) {                                               \
> -                       *str++ = c;                                            \
> +                       *str++ = cc;                                           \
>                         size--;                                                \
>                 }                                                              \
>                 retval++;                                                      \
--
Dr. Florian Schmidt
フローリアン・シュミット
Research Scientist,
Systems and Machine Learning Group
NEC Laboratories Europe
Kurfürsten-Anlage 36, D-69115 Heidelberg
Tel.     +49 (0)6221 4342-265
Fax:     +49 (0)6221 4342-155
e-mail:  florian.schmidt@xxxxxxxxx
============================================================
Registered at Amtsgericht Mannheim, Germany, HRB728558

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