A library's own _Float128 API has no correct mangled name from castxml

Index: Known gaps

Status (re-verified 2026-10-09 at 456989f): OPEN. unverified: castxml mangling was not run. The entry records the defect as an unresolved castxml limitation: _Float128 functions read as not exported.

Found while fixing castxml on binary128 long double targets (extract/ castxml_header_compat.py). The type spelling is right on every target (_Float128), but castxml's mangled attribute for a function taking one is not the Itanium name the compiler emits (_Z2qfDF128_P1Q): on x86-64 castxml reports the bare name (qf), on AArch64 a name embedding the stand-in record (_Z2qf19__abicheck_Float128P1Q). Either way the export join misses, so such a function reads as not exported on both architectures. A token substitution is not a fix (Itanium substitution numbering differs between a class name and a builtin type), so it was not attempted. glibc's own *f128 declarations are system headers and unaffected.