I receive the following warnings in tasks.c in freertos 5.4.1 in IAR arm 5.20 for cortex-m3:
Warning[Pa082]: undefined behavior: the order of volatile accesses is undefined in this statement freeRTOS\tasks.c 611
Warning[Pa082]: undefined behavior: the order of volatile accesses is undefined in this statement freeRTOS\tasks.c 617
Warning[Pa082]: undefined behavior: the order of volatile accesses is undefined in this statement freeRTOS\tasks.c 672
Warning[Pa082]: undefined behavior: the order of volatile accesses is undefined in this statement freeRTOS\tasks.c 678
Warning[Pa082]: undefined behavior: the order of volatile accesses is undefined in this statement freeRTOS\tasks.c 1551
Warning[Pa082]: undefined behavior: the order of volatile accesses is undefined in this statement freeRTOS\tasks.c 1593
Warning[Pa082]: undefined behavior: the order of volatile accesses is undefined in this statement freeRTOS\tasks.c 1598
Warning[Pa082]: undefined behavior: the order of volatile accesses is undefined in this statement freeRTOS\tasks.c 1970
While these warnings seem to have no ill effects, our internal coding standard prohibits having any warnings in our code. Any thoughts on the proper way to resolve these warnings?
The warning is quite correct, but as far as I recall from inspection, also quite benign. It comes from trying to support lots of different compilers, all of which generate warnings in different and sometimes contradictory ways.
You could try casting away the volatile from one or other side of the statement.
I will take a look at the code lines again to see what can be done. In the provided demos I think you will find the warning is just switched off.
I ended up satisfying this warning by forcing the order in which these variables were accessed:
xList xlXList;
xListItem xliXListItem;
…
if( xTimeToWake < xTickCount )
{
/* Wake time has overflowed. Place this item in the
overflow list. */
xlXList = *((xList *) pxOverflowDelayedTaskList);
xliXListItem = *((xListItem *) &( pxCurrentTCB->xGenericListItem ));
vListInsert( &xlXList, &xliXListItem);
}
else
{
/* The wake time has not overflowed, so we can use the
current block list. */
xlXList = *((xList *) pxDelayedTaskList);
xliXListItem = *((xListItem *) &( pxCurrentTCB->xGenericListItem ));
vListInsert( &xlXList, &xliXListItem);
}
wouldn’t this be ‘better’ than just turning off the warning?