A root is a frame word the collector scans for live capabilities: an entry of the Pizderson frame's lowers[] (the record each function keeps on the stack: a parent link, an originorigin Fil-CAn origin is a static record the runtime reads to name a function and source location in a trap or backtrace (filc_amd64:function_origins//3). In context records the word means something else: a typed source node (provenance.pl). and the lowers), a local's stack auxaux Fil-CAn object's aux allocation, as large as its payload: where Fil-C keeps the lowers of the pointers stored in the object, slot for slot, while their intvals sit in the object's bytes. The aux word in the object header points at it; it is null for an object no pointer was ever stored into, which the collector then scans as a leaf. A pointer store must *ensure* it exists, which may call the runtime; a pointer load reads it., or a jmpbuf root (filc_abi:lower_function/5filc_abi.pllower_function+Pools, +Symbols, +FusedFunction, +LiveBlocks, -ProductdetAs lower_function/4, with the temporaries' slot pools shared or own (frame_slots:temp_slots/9)., amd64_regs_check:valid_map/3amd64_regs_check.plMapped homes are disjoint 8-byte homes, every description of each one a scalar (w, l) or a pointer's address word (a), never a pointer (p); no mapped home overlaps a GC root range; save slots match the callee-saved registers used, in order, and lie outside every home.). Every live lowerlower Fil-CThe lower is how Fil-C represents a capability natively: the address of the first byte of the object a pointer may access, kept beside the pointer's intval in a flight pointer. The object header sits just below it: the upper bound at lower−16 and the aux word at lower−8, whose low 48 bits point at the aux allocation and whose top 16 bits hold the object's flags (free, read-only, global, ...). A null lower accesses nothing, and free sets upper to lower, so every access through any lower of a freed object fails. filc_abi:lower_function/5 keeps each live one in a root. is in one at every safepointpoll Fil-CA safepoint is a point where the thread may run signal handlers and answer the collector. The collector frees nothing the program can name there, but a handler the program installed may free an object under the rest of the program. A pollcheck is a safepoint on an edge: a jump target poll(L), a poll edge, runs one before going to L. Calls, allocations and some helpers are safepoints too (ir:evidence_preserving/1, ir:polls_every_cycle/1)., so registers never hold the only copy.

The model has no roots: the runtimeruntime Fil-CThe runtime is what Fil-C does around one thread's program, natively libpizlo.so with FUGC: where a new object goes, what free does, and what the collector may change while the program waits at a safepoint. The model does not define it; it states it as one page of axioms, Module Type Runtime (Runtime), each with a native test in tests/c/prog/axiom-*.c. lemma rooting, from the axiom collector_live, says instead that a safepoint reclaims no identityidentity nanofilAn object's identity is its base, the number its capabilities name; it outlives the object's bounds, so a freed object keeps its identity. One memory persists from another when every object of the first is in the second as it was, or freed: no identity is lost, moved or given to a new object. the program can name.