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

[Jan Kiszka <jan.kiszka@domain.hid>]

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Christoph Permes wrote:
> Am Freitag, den 28.08.2009, 09:38 +0200 schrieb Jan Kiszka:
>> Hmm, strange. Code meditation didn't help, so I need to keep you busy
>> with testing. Could you try this instrumentation? It should choke if the
>> rt_vfprintf actually overwrites already written data.
>>
>> Thanks,
>> Jan
>>
>> diff --git a/src/rtdk/rt_print.c b/src/rtdk/rt_print.c
>> index 0615247..bcd8c88 100644
>> --- a/src/rtdk/rt_print.c
>> +++ b/src/rtdk/rt_print.c
>> @@ -16,6 +16,7 @@
>>   * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA.
>>   */
>>  
>> +#include <assert.h>
>>  #include <errno.h>
>>  #include <inttypes.h>
>>  #include <limits.h>
>> @@ -37,7 +38,10 @@
>>  
>>  #define RT_PRINT_LINE_BREAK		256
>>  
>> +#define RT_PRINT_HEAD_MAGIC		0xDEADBEAF
>> +
>>  struct entry_head {
>> +	uint32_t magic;
>>  	FILE *dest;
>>  	uint32_t seq_no;
>>  	char text[1];
>> @@ -103,6 +107,10 @@ int rt_vfprintf(FILE *stream, const char *format, va_list args)
>>  	read_pos = buffer->read_pos;
>>  	xnarch_read_memory_barrier();
>>  
>> +	assert(write_pos == read_pos ||
>> +	       ((struct entry_head *)buffer->read_pos)->magic ==
>> +	       RT_PRINT_HEAD_MAGIC);
>> +
>>  	/* Is our write limit the end of the ring buffer? */
>>  	if (write_pos >= read_pos) {
>>  		/* Keep a savety margin to the end for at least an empty entry */
>> @@ -114,6 +122,7 @@ int rt_vfprintf(FILE *stream, const char *format, va_list args)
>>  		if (len == 0 && read_pos > sizeof(struct entry_head)) {
>>  			/* Write out empty entry */
>>  			head = buffer->ring + write_pos;
>> +			head->magic = RT_PRINT_HEAD_MAGIC;
>>  			head->seq_no = seq_no;
>>  			head->text[0] = 0;
>>  
>> @@ -136,6 +145,10 @@ int rt_vfprintf(FILE *stream, const char *format, va_list args)
>>  
>>  	res = vsnprintf(head->text, len, format, args);
>>  
>> +	assert(write_pos == read_pos ||
>> +	       ((struct entry_head *)buffer->read_pos)->magic ==
>> +	       RT_PRINT_HEAD_MAGIC);
>> +
>>  	if (res < len) {
>>  		/* Text was written completely, res contains its length */
>>  		len = res;
>> @@ -147,6 +160,7 @@ int rt_vfprintf(FILE *stream, const char *format, va_list args)
>>  
>>  	/* If we were able to write some text, finalise the entry */
>>  	if (len > 0) {
>> +		head->magic = RT_PRINT_HEAD_MAGIC;
>>  		head->seq_no = ++seq_no;
>>  		head->dest = stream;
>>  
>> @@ -159,6 +173,7 @@ int rt_vfprintf(FILE *stream, const char *format, va_list args)
>>  	    read_pos <= write_pos && read_pos > buffer->size - write_pos) {
>>  		/* An empty entry marks the wrap-around */
>>  		head = buffer->ring + write_pos;
>> +		head->magic = RT_PRINT_HEAD_MAGIC;
>>  		head->seq_no = seq_no;
>>  		head->text[0] = 0;
>>  
>> @@ -382,6 +397,8 @@ static void print_buffers(void)
>>  		head = buffer->ring + read_pos;
>>  		len = strlen(head->text);
>>  
>> +		assert(head->magic == RT_PRINT_HEAD_MAGIC);
>> +
>>  		if (len) {
>>  			/* Print out non-empty entry and proceed */
>>  			fprintf(head->dest, "%s", head->text);
>>
> 
> Now I get a SEGV at the first line of the first assert statement
> (assert(write_pos == read_pos || ) in rt_vfprintf.
> This happens at the first rt_printf call, also with the rtprint example
> program.

Untested stuff as I should already be on the road. Here is another try,
but please don't expect replies from me over this weekend.

Jan

diff --git a/src/rtdk/rt_print.c b/src/rtdk/rt_print.c
index 0615247..06dabc1 100644
--- a/src/rtdk/rt_print.c
+++ b/src/rtdk/rt_print.c
@@ -16,6 +16,7 @@
  * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA.
  */
 
+#include <assert.h>
 #include <errno.h>
 #include <inttypes.h>
 #include <limits.h>
@@ -37,7 +38,10 @@
 
 #define RT_PRINT_LINE_BREAK		256
 
+#define RT_PRINT_HEAD_MAGIC		0xDEADBEAF
+
 struct entry_head {
+	uint32_t magic;
 	FILE *dest;
 	uint32_t seq_no;
 	char text[1];
@@ -103,6 +107,10 @@ int rt_vfprintf(FILE *stream, const char *format, va_list args)
 	read_pos = buffer->read_pos;
 	xnarch_read_memory_barrier();
 
+	assert(write_pos == read_pos ||
+	       ((struct entry_head *)buffer->ring + buffer->read_pos)->magic ==
+	       RT_PRINT_HEAD_MAGIC);
+
 	/* Is our write limit the end of the ring buffer? */
 	if (write_pos >= read_pos) {
 		/* Keep a savety margin to the end for at least an empty entry */
@@ -114,6 +122,7 @@ int rt_vfprintf(FILE *stream, const char *format, va_list args)
 		if (len == 0 && read_pos > sizeof(struct entry_head)) {
 			/* Write out empty entry */
 			head = buffer->ring + write_pos;
+			head->magic = RT_PRINT_HEAD_MAGIC;
 			head->seq_no = seq_no;
 			head->text[0] = 0;
 
@@ -136,6 +145,10 @@ int rt_vfprintf(FILE *stream, const char *format, va_list args)
 
 	res = vsnprintf(head->text, len, format, args);
 
+	assert(write_pos == read_pos ||
+	       ((struct entry_head *)buffer->ring + buffer->read_pos)->magic ==
+	       RT_PRINT_HEAD_MAGIC);
+
 	if (res < len) {
 		/* Text was written completely, res contains its length */
 		len = res;
@@ -147,6 +160,7 @@ int rt_vfprintf(FILE *stream, const char *format, va_list args)
 
 	/* If we were able to write some text, finalise the entry */
 	if (len > 0) {
+		head->magic = RT_PRINT_HEAD_MAGIC;
 		head->seq_no = ++seq_no;
 		head->dest = stream;
 
@@ -159,6 +173,7 @@ int rt_vfprintf(FILE *stream, const char *format, va_list args)
 	    read_pos <= write_pos && read_pos > buffer->size - write_pos) {
 		/* An empty entry marks the wrap-around */
 		head = buffer->ring + write_pos;
+		head->magic = RT_PRINT_HEAD_MAGIC;
 		head->seq_no = seq_no;
 		head->text[0] = 0;
 
@@ -382,6 +397,8 @@ static void print_buffers(void)
 		head = buffer->ring + read_pos;
 		len = strlen(head->text);
 
+		assert(head->magic == RT_PRINT_HEAD_MAGIC);
+
 		if (len) {
 			/* Print out non-empty entry and proceed */
 			fprintf(head->dest, "%s", head->text);


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