Function xmlGcMemSetup 

#[unsafe(no_mangle)]
pub unsafe extern "C" fn xmlGcMemSetup(
    freeFunc: Option<xmlFreeFunc>,
    mallocFunc: Option<xmlMallocFunc>,
    mallocAtomicFunc: Option<xmlMallocFunc>,
    reallocFunc: Option<xmlReallocFunc>,
    strdupFunc: Option<xmlStrdupFunc>,
) -> c_int

Set GC-aware memory allocator functions (upstream xmlmemory.h).

UPSTREAM-PARITY

int xmlGcMemSetup(xmlFreeFunc freeFunc,
                  xmlMallocFunc mallocFunc,
                  xmlMallocFunc mallocAtomicFunc,
                  xmlReallocFunc reallocFunc,
                  xmlStrdupFunc strdupFunc);

Same contract as xmlMemSetup with a dedicated mallocAtomicFunc for atomic allocations (upstream xmlmemory.c: xmlMallocAtomic = mallocAtomicFunc). Returns -1 if any function is NULL, else 0.

SAFETY

• All function pointers must be valid (non-null) and thread-safe
• The functions must follow the C malloc/realloc/free/strdup contract
• Must not race with concurrent allocation (upstream ordering contract)
• The caller is responsible for ensuring the functions remain valid for the entire time they are installed