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

[Laurent Vivier <laurent@vivier.eu>]

On 01/05/2019 11:44, Daniel P. Berrangé wrote:
> 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
> 

Yes, it's better.

Thanks,
Laurent