[DTrace-devel] [PATCH 1/2] Possible uninitialized 'last' variable in usdt_copyin_data()

[Eugene Loh]

On 8/15/25 11:25, Kris Van Hees wrote:

> On Tue, Aug 12, 2025 at 06:46:05PM -0400, eugene.loh at oracle.com wrote:
>> From: Eugene Loh <eugene.loh at oracle.com>
>>
>> Some compilers warn:
>>
>> libcommon/usdt_parser.c: In function ???usdt_copyin_data???:
>> libcommon/usdt_parser.c:191:15: warning:
>>     ???last??? may be used uninitialized in this function [-Wmaybe-uninitialized]
>>      last->next = blk;
>>      ~~~~~~~~~~~^~~~~
>>
>> Change the "if" check to make it easier for compilers to recognize
>> that "last" will be initialized (and non-NULL even!).
> I disagree...  What compiler version reported this as a warning?  The warning
> shows a limitation of the compiler to see that last can actually never be
> used uninitialized.

OL8 with "yum update" then "make".  Looks like
gcc (GCC) 8.5.0 20210514 (Red Hat 8.5.0-26.0.1)
Should I be using a different recipe?

At least in my opinion, the new code with this patch is simply cleaner.

> I don't think we should make changes like these to accomodate compielrs that
> are less advanced.  We generally expect systems to be updated to the most
> recent version of packages so that would include the compiler.
>
>> Signed-off-by: Eugene Loh <eugene.loh at oracle.com>
>> ---
>>   libcommon/usdt_parser.c | 4 ++--
>>   1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/libcommon/usdt_parser.c b/libcommon/usdt_parser.c
>> index 864198098..d8cb9b7ba 100644
>> --- a/libcommon/usdt_parser.c
>> +++ b/libcommon/usdt_parser.c
>> @@ -163,7 +163,7 @@ usdt_destroy_data(usdt_data_t *data)
>>   usdt_data_t *
>>   usdt_copyin_data(int in, int out, int *ok)
>>   {
>> -	usdt_data_t *first = NULL, *last;
>> +	usdt_data_t *first = NULL, *last = NULL;
>>   	size_t cnt;
>>   
>>   	*ok = 1;
>> @@ -185,7 +185,7 @@ usdt_copyin_data(int in, int out, int *ok)
>>   		if ((blk = usdt_copyin_block(in, out, ok)) == NULL)
>>   			goto err;
>>   
>> -		if (first == NULL)
>> +		if (last == NULL)
>>   			first = last = blk;
>>   		else {
>>   			last->next = blk;
>> -- 
>> 2.47.3
>>