On Mon, Sep 30, 2019 at 08:40:29PM -0700, Jerry DeLisle wrote:
> Copying gcc list for additional thoughts on a possible bogus warning.
>
> On 9/29/19 9:02 AM, Jerry DeLisle wrote:
> > Hi all,
> >
> --- snip ---
>
> > diff --git a/libgfortran/io/write.c b/libgfortran/io/write.c
> > index 4ef35561fdd..fc046efbe34 100644
> > --- a/libgfortran/io/write.c
> > +++ b/libgfortran/io/write.c
> > @@ -1031,7 +1031,7 @@ btoa_big (const char *s, char *buffer, int len,
> > GFC_UINTEGER_LARGEST *n)
> > else
> > {
> > const char *p = s + len - 1;
> > - for (i = 0; i < len; i++)
> > + for (i = 0; i < len - 1; i++)
> > {
> > char c = *p;
> >
>
> --- snip ---
>
> The first attempt to fix (above) is completely off. I have tried various
> combinations of code changes and I am beginning to think the warning is bogus:
>
> In function ‘btoa_big’,
> inlined from ‘write_b’ at ../../../trunk/libgfortran/io/write.c:1217:11:
> ../../../trunk/libgfortran/io/write.c:1052:6: warning: writing 1 byte into a
> region of size 0 [-Wstringop-overflow=]
> 1052 | *q = '\0';
> | ~~~^~~~~~
>
> Using gdb I have watched the pointer address stored in q and the setting of
> the
> string of bytes doing the binary to ascii conversion. I have also checked the
> length of the buffer being used and its is what I would expect with length of
> 129.
>
> However, the warning only goes away if I add an additional 8 bytes to the
> buffer
> (suspicious).
>
> So doing the following eliminates the warning:
>
> diff --git a/libgfortran/io/write.c b/libgfortran/io/write.c
> index 4ef35561fdd..fd0e46851e4 100644
> --- a/libgfortran/io/write.c
> +++ b/libgfortran/io/write.c
> @@ -1204,7 +1204,7 @@ void
> write_b (st_parameter_dt *dtp, const fnode *f, const char *source, int len)
> {
> const char *p;
> - char itoa_buf[GFC_BTOA_BUF_SIZE];
> + char itoa_buf[GFC_BTOA_BUF_SIZE + 8];
> GFC_UINTEGER_LARGEST n = 0;
>
> if (len > (int) sizeof (GFC_UINTEGER_LARGEST))
>
> Any suggestions? I am certainly not seeing it.
>
Can you just zero memory and remove the explicit setting
of the terminating '\0'?
q = buffer;
memset(q, 0, len);
--
Steve
