Re: [Qemu-devel] [PATCH v3 2/5] block/sheepdog: Use QEMU_NONSTRING for non NUL-terminated arrays

[Philippe Mathieu-Daudé]

Le mer. 19 déc. 2018 00:09, Michael S. Tsirkin <address@hidden> a écrit :

> On Tue, Dec 18, 2018 at 06:51:19PM +0100, Philippe Mathieu-Daudé wrote:
> > GCC 8 added a -Wstringop-truncation warning:
> >
> >   The -Wstringop-truncation warning added in GCC 8.0 via r254630 for
> >   bug 81117 is specifically intended to highlight likely unintended
> >   uses of the strncpy function that truncate the terminating NUL
> >   character from the source string.
> >
> > This new warning leads to compilation failures:
> >
> >     CC      block/sheepdog.o
> >   qemu/block/sheepdog.c: In function 'find_vdi_name':
> >   qemu/block/sheepdog.c:1239:5: error: 'strncpy' specified bound 256
> equals destination size [-Werror=stringop-truncation]
> >        strncpy(buf + SD_MAX_VDI_LEN, tag, SD_MAX_VDI_TAG_LEN);
> >        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> >   make: *** [qemu/rules.mak:69: block/sheepdog.o] Error 1
> >
> > As described previous to the strncpy() calls, the use of strncpy() is
> > correct here:
> >
> >     /* This pair of strncpy calls ensures that the buffer is zero-filled,
> >      * which is desirable since we'll soon be sending those bytes, and
> >      * don't want the send_req to read uninitialized data.
> >      */
> >     strncpy(buf, filename, SD_MAX_VDI_LEN);
> >     strncpy(buf + SD_MAX_VDI_LEN, tag, SD_MAX_VDI_TAG_LEN);
> >
> > Use the QEMU_NONSTRING attribute, since this array is intended to store
> > character arrays that do not necessarily contain a terminating NUL.
> >
> > Suggested-by: Michael S. Tsirkin <address@hidden>
> > Signed-off-by: Philippe Mathieu-Daudé <address@hidden>
> > ---
> >  block/sheepdog.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/block/sheepdog.c b/block/sheepdog.c
> > index 0125df9d49..d4ad6b119d 100644
> > --- a/block/sheepdog.c
> > +++ b/block/sheepdog.c
> > @@ -1224,7 +1224,7 @@ static int find_vdi_name(BDRVSheepdogState *s,
> const char *filename,
> >      SheepdogVdiReq hdr;
> >      SheepdogVdiRsp *rsp = (SheepdogVdiRsp *)&hdr;
> >      unsigned int wlen, rlen = 0;
> > -    char buf[SD_MAX_VDI_LEN + SD_MAX_VDI_TAG_LEN];
> > +    QEMU_NONSTRING char buf[SD_MAX_VDI_LEN + SD_MAX_VDI_TAG_LEN];
>
> In case you decide to respin anyway - this would be
> a bit nicer as:
>         char buf[SD_MAX_VDI_LEN + SD_MAX_VDI_TAG_LEN] QEMU_NONSTRING
>

I'll have to, so OK.
(it looked to me more explicit prepended).


>
>
>
> >      fd = connect_to_sdog(s, errp);
> >      if (fd < 0) {
> > --
> > 2.17.2
>