🍒 [lldb] Fix ThreadPlanStepOut::DoPlanExplainsStop inspection of BreakpointSite (#169799) #11919
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…ointSite (llvm#169799) Suppose two threads are performing the exact same step out plan. They will both have an internal breakpoint set at their parent frame. Now supposed both of those breakpoints are in the same address (i.e. the same BreakpointSite). At the end of `ThreadPlanStepOut::DoPlanExplainsStop`, we see this: ``` // If there was only one owner, then we're done. But if we also hit // some user breakpoint on our way out, we should mark ourselves as // done, but also not claim to explain the stop, since it is more // important to report the user breakpoint than the step out // completion. if (site_sp->GetNumberOfConstituents() == 1) return true; ``` In other words, the plan looks at the name number of constituents of the site to decide whether it explains the stop, the logic being that a _user_ might have put a breakpoint there. However, the implementation is not correct; in particular, it will fail in the situation described above. We should only care about non-internal breakpoints that would stop for the current thread. It is tricky to test this, as it depends on the timing of threads, but I was able to consistently reproduce the issue with a swift program using concurrency. rdar://165481473 (cherry picked from commit c0f0936)
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adrian-prantl
approved these changes
Dec 4, 2025
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Suppose two threads are performing the exact same step out plan. They will both have an internal breakpoint set at their parent frame. Now supposed both of those breakpoints are in the same address (i.e. the same BreakpointSite).
At the end of
ThreadPlanStepOut::DoPlanExplainsStop, we see this:In other words, the plan looks at the name number of constituents of the site to decide whether it explains the stop, the logic being that a user might have put a breakpoint there. However, the implementation is not correct; in particular, it will fail in the situation described above. We should only care about non-internal breakpoints that would stop for the current thread.
It is tricky to test this, as it depends on the timing of threads, but I was able to consistently reproduce the issue with a swift program using concurrency.
rdar://165481473
(cherry picked from commit c0f0936)