writeBlock(ctxt, o, ldr, syms, addr, size, pad)
				wg.Done()
				<-sem
			}(o, ldr, syms, addr, length, pad)
		} else { // output not mmaped, don't parallelize.
			writeBlock(ctxt, out, ldr, syms, addr, length, pad)
		}

		// Prepare for the next loop.
		if idx != -1 {
			syms = syms[idx+1:]
		}
		written += length