Re: [Xenomai-help] Segmentation fault in rt_printf print thread

[Gilles Chanteperdrix <gilles.chanteperdrix@xenomai.org>]

Jan Kiszka wrote:
> Christoph Permes wrote:
>> Hi, 
>>
>> I've created a patch that provides a workaround for the segmentation
>> fault:
>>
>> --- a/src/rtdk/rt_print.c	2009-05-21 16:34:54.000000000 +0200
>> +++ b/src/rtdk/rt_print.c	2009-09-04 10:09:19.000000000 +0200
>> @@ -40,6 +40,7 @@
>>  struct entry_head {
>>  	FILE *dest;
>>  	uint32_t seq_no;
>> +	uint32_t len;
>>  	char text[1];
>>  } __attribute__((packed));
>>  
>> @@ -113,6 +114,7 @@
>>  			/* Write out empty entry */
>>  			head = buffer->ring + write_pos;
>>  			head->seq_no = __seq_no;
>> +			head->len = 0;
>>  			head->text[0] = 0;
>>  
>>  			/* Forward to the ring buffer start */
>> @@ -146,6 +148,7 @@
>>  	/* If we were able to write some text, finalise the entry */
>>  	if (len > 0) {
>>  		head->seq_no = ++__seq_no;
>> +		head->len = len;
>>  		head->dest = stream;
>>  
>>  		/* Move forward by text and head length */
>> @@ -158,6 +161,7 @@
>>  		/* An empty entry marks the wrap-around */
>>  		head = buffer->ring + write_pos;
>>  		head->seq_no = __seq_no;
>> +		head->len = 0;
>>  		head->text[0] = 0;
>>  
>>  		write_pos = 0;
>> @@ -373,7 +377,7 @@
>>  
>>  		read_pos = buffer->read_pos;
>>  		head = buffer->ring + read_pos;
>> -		len = strlen(head->text);
>> +		len = head->len;
>>  
>>  		if (len) {
>>  			/* Print out non-empty entry and proceed */
>>
>> With this patch I get no segfaults anymore, but of course it would be
>> interesting why parts of the ring buffer are overwritten with null
>> characters.
>>
> 
> Frankly, I'm suspecting some issue in your application here - at least
> as long as you do not have some broken-out test case for us...

Would not it be possible to mprotect the rtdk buffer when it is not used
in order to catch any write to it outside of rtdk functions?

-- 
                                          Gilles