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050cf0d80f
The introduction of `portMEMORY_BARRIER` will ensure the places in the kernel use a barrier will work. For example, `xTaskResumeAll` has a memory barrier to ensure its correctness when compiled with optimization enabled. Without the barrier `xTaskResumeAll` can fail (e.g. start reading and writing to address 0 and/or infinite looping) when `xPendingReadyList` contains more than one task to restore. In `xTaskResumeAll` the compiler chooses to cache the `pxTCB` the first time through the loop for use in every subsequent loop. This is incorrect as the removal of `pxTCB->xEventListItem` will actually change the value of `pxTCB` if it was read again at the top of the loop. The barrier forces the compiler to read `pxTCB` again at the top of the loop. The compiler is operating correctly. The removal `pxTCB->xEventListItem` executes on a `List_t *` and `ListItem_t *`. This means that the compiler can assume that any `MiniListItem_t` values are unchanged by the loop (i.e. "strict-aliasing"). This allows the compiler to cache `pxTCB` as it is obtained via a `MiniListItem_t`. This is incorrect in this case because it is possible for a `ListItem_t *` to actually alias a `MiniListItem_t`. This is technically a "violation of aliasing rules" so we use the the barrier to disable the strict-aliasing optimization in this loop. |
2 years ago | |
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| .. | ||
| port.c | 2 years ago | |
| portasm.s | 2 years ago | |
| portmacro.h | 2 years ago | |