Safety

Exceptions

An exception can't propagate through the assembly switch; that would be undefined behavior. ucoro catches it at the coroutine boundary and keeps it as a std::exception_ptr, which the caller can inspect or rethrow after resume() returns.

resume_unchecked() does not check for a captured exception. Use it only when the body can't throw.

Guard pages

On Linux, macOS and Windows, stacks come from mmap/VirtualAlloc with a guard page between the metadata and the stack. An overflow faults (SIGSEGV or an access violation) instead of corrupting the memory next to it.

#define UCORO_GUARD_PAGES 0 turns this off, for embedded targets or custom allocators.

Overflow checks

The checked yield() also compares the stack pointer against the coroutine's stack bounds and checks a magic number, so an overflow is caught at the next yield even without guard pages.