Re: [PATCH] tools/xenmpd: Fix gcc10 snprintf warning

[Bertrand Marquis <Bertrand.Marquis@arm.com>]

Hi Julien,

> On 14 Oct 2020, at 12:04, Julien Grall <julien@xen.org> wrote:
> 
> Hi,
> 
> On 14/10/2020 11:47, Bertrand Marquis wrote:
>> Add a check for snprintf return code and ignore the entry if we get an
>> error. This should in fact never happen and is more a trick to make gcc
>> happy and prevent compilation errors.
>> This is solving the gcc warning:
>> xenpmd.c:92:37: error: '%s' directive output may be truncated writing
>> between 4 and 2147483645 bytes into a region of size 271
>> [-Werror=format-truncation=]
> 
> IIRC, this is only affecting GCC when building for Arm32 *and* when the optimizer is enabled. If so, it would be good to add more details in the commit message.

I can confirm this is the only build catching it on my side.

I will modify the commit message to say that the problem was encountered on arm32 build with the optimizer enabled.

> 
> I would also suggest to link to the bug reported on Debian.

I will add it to the commit message.

Cheers
Bertrand

> 
> Cheers,
> 
>> Signed-off-by: Bertrand Marquis <bertrand.marquis@arm.com>
>> ---
>>  tools/xenpmd/xenpmd.c | 9 +++++++--
>>  1 file changed, 7 insertions(+), 2 deletions(-)
>> diff --git a/tools/xenpmd/xenpmd.c b/tools/xenpmd/xenpmd.c
>> index 35fd1c931a..12b82cf43e 100644
>> --- a/tools/xenpmd/xenpmd.c
>> +++ b/tools/xenpmd/xenpmd.c
>> @@ -102,6 +102,7 @@ FILE *get_next_battery_file(DIR *battery_dir,
>>      FILE *file = 0;
>>      struct dirent *dir_entries;
>>      char file_name[284];
>> +    int ret;
>>            do
>>      {
>> @@ -111,11 +112,15 @@ FILE *get_next_battery_file(DIR *battery_dir,
>>          if ( strlen(dir_entries->d_name) < 4 )
>>              continue;
>>          if ( battery_info_type == BIF )
>> -            snprintf(file_name, sizeof(file_name), BATTERY_INFO_FILE_PATH,
>> +            ret = snprintf(file_name, sizeof(file_name), BATTERY_INFO_FILE_PATH,
>>                       dir_entries->d_name);
>>          else
>> -            snprintf(file_name, sizeof(file_name), BATTERY_STATE_FILE_PATH,
>> +            ret = snprintf(file_name, sizeof(file_name), BATTERY_STATE_FILE_PATH,
>>                       dir_entries->d_name);
>> +        /* This should not happen but is needed to pass gcc checks */
>> +        if (ret < 0)
>> +            continue;
>> +        file_name[sizeof(file_name) - 1] = '\0';
>>          file = fopen(file_name, "r");
>>      } while ( !file );
>>  
> 
> Cheers,
> 
> -- 
> Julien Grall