Tried -fno-builtin-malloc on a hunch and it does seem to prevent the zero-initialisation logic from getting optimised away: https://godbolt.org/z/xWbEqcenn http

Tried -fno-builtin-malloc on a hunch and it does seem to prevent the zero-initialisation logic from getting optimised away: https://godbolt.org/z/xWbEqcenn https://godbolt.org/z/xWbEqcenn musl probably uses -fno-builtin to disable any special handling of "builtin" library functions like malloc and memcpy?