Subject: redundant user mode check in syscall handling Index: sys/pdp/trap.c 2.11BSD Description: There is a redundant test for a syscall originating in user mode. This test has already been performed by the assembly routine which receives the 'trap' instruction. The second test (which works out to 4 instructions per syscall) can safely be removed. Repeat-By: Examine the code. Look in sys/pdp/mch_trap.s in the routine ASENTRY(syscall) and see the test for the 'trap' instruction originating in user mode. Fix: Apply the following patch and reinstall the kernel. ========================================================================== *** /sys/pdp/trap.c.old Mon Aug 19 17:46:46 1991 --- /sys/pdp/trap.c Fri Feb 7 18:20:32 1992 *************** *** 355,362 **** cnt.v_syscall++; #endif - if (!USERMODE(ps)) - panic("syscall"); syst = u.u_ru.ru_stime; #ifndef NONFP u.u_fpsaved = 0; --- 355,360 ----