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Help students read this C syntax

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This commit is contained in:
Frans Kaashoek 2022-08-24 08:57:56 -04:00
parent 96047832c6
commit cc486ddee0
1 changed files with 5 additions and 0 deletions
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5
kernel/syscall.c
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@ -79,6 +79,7 @@ argstr(int n, char *buf, int max)
return fetchstr(addr, buf, max); return fetchstr(addr, buf, max);
} }
// Prototypes for the functions that handle system calls.
extern uint64 sys_fork(void); extern uint64 sys_fork(void);
extern uint64 sys_exit(void); extern uint64 sys_exit(void);
extern uint64 sys_wait(void); extern uint64 sys_wait(void);
@ -101,6 +102,8 @@ extern uint64 sys_link(void);
extern uint64 sys_mkdir(void); extern uint64 sys_mkdir(void);
extern uint64 sys_close(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) = { static uint64 (*syscalls[])(void) = {
[SYS_fork] sys_fork, [SYS_fork] sys_fork,
[SYS_exit] sys_exit, [SYS_exit] sys_exit,
@ -133,6 +136,8 @@ syscall(void)
num = p->trapframe->a7; num = p->trapframe->a7;
if(num > 0 && num < NELEM(syscalls) && syscalls[num]) { 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](); p->trapframe->a0 = syscalls[num]();
} else { } else {
printf("%d %s: unknown sys call %d\n", printf("%d %s: unknown sys call %d\n",