ax_cpu/aarch64/
uspace.rs

1//! Structures and functions for user space.
2
3use core::ops::{Deref, DerefMut};
4
5use aarch64_cpu::registers::{ESR_EL1, FAR_EL1, Readable};
6use ax_memory_addr::VirtAddr;
7use tock_registers::LocalRegisterCopy;
8
9use super::trap::{TrapKind, is_valid_page_fault};
10pub use crate::uspace_common::{ExceptionKind, ReturnReason};
11use crate::{TrapFrame, trap::PageFaultFlags};
12
13/// Context to enter user space.
14#[repr(C, align(16))]
15#[derive(Debug, Clone, Copy)]
16pub struct UserContext {
17    tf: TrapFrame,
18    /// Stack Pointer (SP_EL0).
19    pub sp: u64,
20    /// Software Thread ID Register (TPIDR_EL0).
21    pub tpidr: u64,
22}
23
24impl UserContext {
25    const PAD_MAGIC: u64 = 0x1234_5678_9abc_def0;
26    /// Creates a new context with the given entry point, user stack pointer,
27    /// and the argument.
28    pub fn new(entry: usize, ustack_top: VirtAddr, arg0: usize) -> Self {
29        use aarch64_cpu::registers::SPSR_EL1;
30        let mut regs = [0; 31];
31        regs[0] = arg0 as _;
32        Self {
33            tf: TrapFrame {
34                x: regs,
35                elr: entry as _,
36                spsr: (SPSR_EL1::M::EL0t
37                    + SPSR_EL1::D::Masked
38                    + SPSR_EL1::A::Masked
39                    + SPSR_EL1::I::Unmasked
40                    + SPSR_EL1::F::Masked)
41                    .value,
42                __pad: Self::PAD_MAGIC,
43            },
44            sp: ustack_top.as_usize() as _,
45            tpidr: 0,
46        }
47    }
48
49    /// Gets the stack pointer.
50    pub const fn sp(&self) -> usize {
51        self.sp as _
52    }
53
54    /// Sets the stack pointer.
55    pub const fn set_sp(&mut self, sp: usize) {
56        self.sp = sp as _;
57    }
58
59    /// Gets the TLS area.
60    pub const fn tls(&self) -> usize {
61        self.tpidr as _
62    }
63
64    /// Sets the TLS area.
65    pub const fn set_tls(&mut self, tls: usize) {
66        self.tpidr = tls as _;
67    }
68
69    /// Enters user space.
70    ///
71    /// It restores the user registers and jumps to the user entry point
72    /// (saved in `elr`).
73    ///
74    /// This function returns when an exception or syscall occurs.
75    pub fn run(&mut self) -> ReturnReason {
76        extern "C" {
77            fn enter_user(uctx: &mut UserContext) -> TrapKind;
78        }
79
80        crate::asm::disable_irqs();
81        let kind = unsafe { enter_user(self) };
82
83        let ret = match kind {
84            TrapKind::Irq => {
85                crate::trap::irq_handler(0);
86                ReturnReason::Interrupt
87            }
88            TrapKind::Fiq | TrapKind::SError => ReturnReason::Unknown,
89            TrapKind::Synchronous => {
90                let esr = ESR_EL1.extract();
91                let far = FAR_EL1.get() as usize;
92
93                let iss = esr.read(ESR_EL1::ISS);
94
95                match esr.read_as_enum(ESR_EL1::EC) {
96                    Some(ESR_EL1::EC::Value::SVC64) => ReturnReason::Syscall,
97                    Some(ESR_EL1::EC::Value::InstrAbortLowerEL) if is_valid_page_fault(iss) => {
98                        ReturnReason::PageFault(
99                            va!(far),
100                            PageFaultFlags::EXECUTE | PageFaultFlags::USER,
101                        )
102                    }
103                    Some(ESR_EL1::EC::Value::DataAbortLowerEL) if is_valid_page_fault(iss) => {
104                        let wnr = (iss & (1 << 6)) != 0; // WnR: Write not Read
105                        let cm = (iss & (1 << 8)) != 0; // CM: Cache maintenance
106                        ReturnReason::PageFault(
107                            va!(far),
108                            if wnr & !cm {
109                                PageFaultFlags::WRITE
110                            } else {
111                                PageFaultFlags::READ
112                            } | PageFaultFlags::USER,
113                        )
114                    }
115                    _ => ReturnReason::Exception(ExceptionInfo { esr, far }),
116                }
117            }
118        };
119
120        crate::asm::enable_irqs();
121        ret
122    }
123}
124
125impl Deref for UserContext {
126    type Target = TrapFrame;
127
128    fn deref(&self) -> &Self::Target {
129        &self.tf
130    }
131}
132
133impl DerefMut for UserContext {
134    fn deref_mut(&mut self) -> &mut Self::Target {
135        &mut self.tf
136    }
137}
138
139/// Information about an exception that occurred in user space.
140#[derive(Debug, Clone, Copy)]
141pub struct ExceptionInfo {
142    /// Exception Syndrome Register
143    pub esr: LocalRegisterCopy<u64, ESR_EL1::Register>,
144    /// Fault Address Register
145    pub far: usize,
146}
147
148impl ExceptionInfo {
149    /// Returns a generalized kind of this exception.
150    pub fn kind(&self) -> ExceptionKind {
151        match self.esr.read_as_enum(ESR_EL1::EC) {
152            Some(ESR_EL1::EC::Value::Brk64) | Some(ESR_EL1::EC::Value::Bkpt32) => {
153                ExceptionKind::Breakpoint
154            }
155            Some(ESR_EL1::EC::Value::IllegalExecutionState) => ExceptionKind::IllegalInstruction,
156            Some(ESR_EL1::EC::Value::PCAlignmentFault)
157            | Some(ESR_EL1::EC::Value::SPAlignmentFault) => ExceptionKind::Misaligned,
158            _ => ExceptionKind::Other,
159        }
160    }
161}
ax_cpu/aarch64/uspace.rs

ax_cpu/aarch64/
uspace.rs
