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

[Eric Blake <eblake@redhat.com>]

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On 5/1/19 4:40 AM, 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.

No, the NUL character is already present, due to the memset() prior to
any use of COPY_UTSNAME_FIELD().  However, the commit message should
call that out, as it is not part of the default 3-line diff.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org


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