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Merge pull request #11540 from opensourcerouting/typesafe-assume-explain

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lib: use assume() for SA fixing, add explainer
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Mark Stapp 2022-07-06 09:52:05 -04:00 committed by GitHub
commit bd7e1bf675
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1 changed files with 20 additions and 2 deletions
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22
lib/typesafe.h
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@ -308,9 +308,27 @@ struct dlist_head {
static inline void typesafe_dlist_add(struct dlist_head *head,
struct dlist_item *prev, struct dlist_item *item)
{
/* SA on clang-11 thinks this can happen, but in reality -assuming no
* memory corruption- it can't. DLIST uses a "closed" ring, i.e. the
* termination at the end of the list is not NULL but rather a pointer
* back to the head. (This eliminates special-casing the first or last
* item.)
*
* Sadly, can't use assert() here since the libfrr assert / xref code
* uses typesafe lists itself... that said, if an assert tripped here
* we'd already be way past some memory corruption, so we might as
* well just take the SEGV. (In the presence of corruption, we'd see
* random SEGVs from places that make no sense at all anyway, an
* assert might actually be a red herring.)
*
* ("assume()" tells the compiler to produce code as if the condition
* will always hold; it doesn't have any actual effect here, it'll
* just SEGV out on "item->next->prev = item".)
*/
assume(prev->next != NULL);
item->next = prev->next;
if (item->next)
item->next->prev = item;
item->next->prev = item;
item->prev = prev;
prev->next = item;
head->count++;