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update ch4 with more comments

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This commit is contained in:
Yu Chen 2022-03-26 21:34:42 +08:00
parent 76056c8626
commit 5946903948
24 changed files with 205 additions and 20 deletions
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13
os/src/syscall/mod.rs
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@ -1,3 +1,15 @@
//! Implementation of syscalls
//!
//! The single entry point to all system calls, [`syscall()`], is called
//! whenever userspace wishes to perform a system call using the `ecall`
//! instruction. In this case, the processor raises an 'Environment call from
//! U-mode' exception, which is handled as one of the cases in
//! [`crate::trap::trap_handler`].
//!
//! For clarity, each single syscall is implemented as its own function, named
//! `sys_` then the name of the syscall. You can find functions like this in
//! submodules, and you should also implement syscalls this way.
const SYSCALL_WRITE: usize = 64;
const SYSCALL_EXIT: usize = 93;
const SYSCALL_YIELD: usize = 124;
@ -9,6 +21,7 @@ mod process;
use fs::*;
use process::*;
/// handle syscall exception with `syscall_id` and other arguments
pub fn syscall(syscall_id: usize, args: [usize; 3]) -> isize {
match syscall_id {
SYSCALL_WRITE => sys_write(args[0], args[1] as *const u8, args[2]),