The library procedure . . . executes a TRAP instruction to switch from user mode to kernel mode and start execution . . . ↑ Context switch#User and kernel mode switching 1 2 Chia-Che, Tsai; Arora, Kumar-Saurabh; Bandi, Nehal; Jain, Bhushan; Jannen, William; John, Jitin; Kalodner, Harry; Kulkarni, Vrushali; Oliviera, Daniela; Porter, Donald E. (2014).