Re: [Qemu-devel] [PATCH v2 4/5] linux-user/uname: Fix GCC 9 build warnings

["Daniel P. Berrangé" <berrange@redhat.com>]

On Wed, May 01, 2019 at 11:40:13AM +0200, Laurent Vivier wrote:
> On 01/05/2019 01:28, Alistair Francis wrote:
> > Fix this warning when building with GCC9 on Fedora 30:
> > In function ‘strncpy’,
> >     inlined from ‘sys_uname’ at /home/alistair/qemu/linux-user/uname.c:94:3:
> > /usr/include/bits/string_fortified.h:106:10: error: ‘__builtin_strncpy’ output may be truncated copying 64 bytes from a string of length 64 [-Werror=stringop-truncation]
> >   106 |   return __builtin___strncpy_chk (__dest, __src, __len, __bos (__dest));
> >       |          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > 
> > Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
> > ---
> >  linux-user/uname.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/linux-user/uname.c b/linux-user/uname.c
> > index 313b79dbad..2fc6096a5b 100644
> > --- a/linux-user/uname.c
> > +++ b/linux-user/uname.c
> > @@ -73,7 +73,7 @@ const char *cpu_to_uname_machine(void *cpu_env)
> >  #define COPY_UTSNAME_FIELD(dest, src) \
> >    do { \
> >        /* __NEW_UTS_LEN doesn't include terminating null */ \
> > -      (void) strncpy((dest), (src), __NEW_UTS_LEN); \
> > +      (void) memcpy((dest), (src), MIN(strlen(src), __NEW_UTS_LEN)); \
> 
> You should use MIN(strlen(src) + 1, __NEW_UTS_LEN) to copy the NUL
> character if it is present and fit in __NEW_UTS_LEN.

IMHO we shouldn't use strlen at all. I proposed fixing it using sizeof()
instead here:

  https://lists.gnu.org/archive/html/qemu-devel/2019-04/msg02154.html

> 
> >        (dest)[__NEW_UTS_LEN] = '\0'; \
> >    } while (0)

Regards,
Daniel
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