Our FreeBSD headers have `pthread_getattr_np`, but we get a link-time
error that is missing. The good news is that there is another similar
function which does exist, and the upstream project elsewhere does just
the [fallback code] we need.
As the fallback code indicates, the two functions are not identical
however as the other one needs explicit initialization. NetBSD supports
both in fact, and its [manpage] is therefore a good
resource on what the differences are.
[fallback code]: 07a6d0ee88/os_dep.c (L1266-L1272)
[manpage]: https://man.netbsd.org/pthread_attr_get_np.3
It is still necessary.
Please do your research, or f ask the author, which happens to be me.
An evaluator like this is not an environment where "it compiles, so
it works" will ever hold.
This reverts commit 1c40182b12.
The darwin_stop_world implementation is slightly different. sp goes to
altstack_lo instead of lo in this case. Assuming that is an
implementation detail.
But the fix is the same, when we detect alstack_lo outside of the
expected stack range, we reset it to hi - stack_limit.
Here stack_limit is calculated with pthread_get_stacksize_np since
that is the BSD equivalent to pthread_attr_getstacksize.
Fixes the problem where a stack pointer outside the original
thread causes the collector to crash.
It could be made more accurate by recording the stack pointer
every time we switch to a coroutine. We can use this information
to update our own coroutine stacks like normal data. When the
stack pointer is on a thread, we can add a field to GC_thread
"fallback_sp" to be used when the thread sp is outside the original
thread range.
