From cc486ddee0c617ab2a0bd000b4674e1094661386 Mon Sep 17 00:00:00 2001 From: Frans Kaashoek Date: Wed, 24 Aug 2022 08:57:56 -0400 Subject: [PATCH] Help students read this C syntax --- kernel/syscall.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/kernel/syscall.c b/kernel/syscall.c index ee94696..ed65409 100644 --- a/kernel/syscall.c +++ b/kernel/syscall.c @@ -79,6 +79,7 @@ argstr(int n, char *buf, int max) return fetchstr(addr, buf, max); } +// Prototypes for the functions that handle system calls. extern uint64 sys_fork(void); extern uint64 sys_exit(void); extern uint64 sys_wait(void); @@ -101,6 +102,8 @@ extern uint64 sys_link(void); extern uint64 sys_mkdir(void); extern uint64 sys_close(void); +// An array mapping syscall numbers from syscall.h +// to the function that handles the system call. static uint64 (*syscalls[])(void) = { [SYS_fork] sys_fork, [SYS_exit] sys_exit, @@ -133,6 +136,8 @@ syscall(void) num = p->trapframe->a7; if(num > 0 && num < NELEM(syscalls) && syscalls[num]) { + // Use num to lookup the system call function for num, call it, + // and store its return value in p->trapframe->a0 p->trapframe->a0 = syscalls[num](); } else { printf("%d %s: unknown sys call %d\n",