I want to do the same as in How to watch a member of a struct for every struct variable that has that type? - but I am on embedded, and have a problem. Say, I want to watch ((TCB_t*)pxReadyTasksLists[1].pxIndex.pxNext.pvOwner).xTaskRunState, however, pxReadyTasksLists is dynamically allocated array of structs, and so I don't have an absolute address I can use at "compile" time. So I tried this in gdb after my main function has advanced enough, so pxReadyTasksLists is allocated:
(gdb) p &(((TCB_t*)pxReadyTasksLists[1].pxIndex.pxNext.pvOwner))
$41 = (TCB_t **) 0x200015c4 <pxReadyTasksLists+40>
Good, so I have what looks like an accessible address here; however, if I try to find the address of the field:
(gdb) p &(((TCB_t*)pxReadyTasksLists[1].pxIndex.pxNext.pvOwner).xTaskRunState)
$43 = (volatile TaskRunning_t *) 0x38
(gdb) ptype TaskRunning_t
type = long int
... I get 0x38, which is kind of suspicious to me; in fact, that is the offset of the field in the struct:
(gdb) ptype /o (TCB_t*)pxReadyTasksLists[1].pxIndex.pxNext.pvOwner
type = struct tskTaskControlBlock {
/* 0 | 4 */ volatile StackType_t *pxTopOfStack;
/* 4 | 4 */ UBaseType_t uxCoreAffinityMask;
/* 8 | 20 */ ListItem_t xStateListItem;
/* 28 | 20 */ ListItem_t xEventListItem;
/* 48 | 4 */ UBaseType_t uxPriority;
/* 52 | 4 */ StackType_t *pxStack;
/* 56 | 4 */ volatile TaskRunning_t xTaskRunState;
/* 60 | 4 */ BaseType_t xIsIdle;
/* 64 | 16 */ char pcTaskName[16];
/* 80 | 4 */ UBaseType_t uxCriticalNesting;
/* 84 | 4 */ UBaseType_t uxTCBNumber;
/* 88 | 4 */ UBaseType_t uxTaskNumber;
/* 92 | 4 */ UBaseType_t uxBasePriority;
/* 96 | 4 */ UBaseType_t uxMutexesHeld;
/* 100 | 20 */ void *pvThreadLocalStoragePointers[5];
/* 120 | 12 */ volatile uint32_t ulNotifiedValue[3];
/* 132 | 3 */ volatile uint8_t ucNotifyState[3];
/* 135 | 1 */ uint8_t ucDelayAborted;
/* total size (bytes): 136 */
} *
(gdb) p /x 56
$46 = 0x38
So, obviously a watchpoint on address 0x38 would not (and does not) trigger.
I can of course calculate 0x200015c4+0x38 and set a "long int" watch there; but then, if I re-run the program in gdb, as pxReadyTasksLists is dynamically allocated, its base address will change, and so will ultimately the address of the particular xTaskRunState that I want to watch.
So in this case, is it possible to craft an expression, which gdb can use to derive the absolute address of (here) pxReadyTasksLists[1].pxIndex.pxNext.pvOwner.xTaskRunState, such that I can set a watchpoint on that address?
