src/starnix/kernel/core/arch/arm64/task.rs

// Copyright 2023 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

use crate::task::PageFaultExceptionReport;
use starnix_uapi::signals::{SIGFPE, Signal};

// See https://developer.arm.com/documentation/ddi0601/2022-03/AArch64-Registers/ESR-EL1--Exception-Syndrome-Register--EL1-
// for details about the values used in this file.

// Returns "Exception Class" from the exception context.
fn get_ec_from_exception_context(arch: &zx::ExceptionArchData) -> u8 {
    // Exception Class is bits 26-31 (inclusive).
    ((arch.esr >> 26) & 0b111111u32) as u8
}

// Returns "Instruction Specific Syndrome" from the exception context.
fn get_iss_from_exception_context(arch: &zx::ExceptionArchData) -> u32 {
    // ISS is bits 0-24 (inclusive).
    arch.esr & 0xffffffu32
}

pub fn decode_page_fault_exception_report(
    arch: &zx::ExceptionArchData,
) -> PageFaultExceptionReport {
    let faulting_address = arch.far;

    let ec = get_ec_from_exception_context(arch);
    let iss = get_iss_from_exception_context(arch);

    let is_execute = ec == 0b100000 || ec == 0b100001; // Instruction abort exceptions.
    let data_abort = ec == 0b100100 || ec == 0b100101; // Data abort exceptions.

    // Data Fault Status Code or Instruction Fault Status Code (bits [0:5] of ISS).
    let dfsc = iss & 0b111111;

    // Translation faults, level 0-3.
    let not_present =
        (dfsc == 0b000100) || (dfsc == 0b000101) || (dfsc == 0b000110) || (dfsc == 0b000111);

    // Note that the Zircon exception handler arm64_data_abort_handler() adds some
    // extra checking of the "cache maintenance" bit which causes it to treat more
    // things as reads. We may need similar handling.
    let is_write = data_abort && (arch.esr & 0b1000000 != 0); // WnR "write not read" = bit 6.

    PageFaultExceptionReport { faulting_address, not_present, is_write, is_execute }
}

pub fn get_signal_for_general_exception(arch: &zx::ExceptionArchData) -> Option<Signal> {
    match get_ec_from_exception_context(arch) {
        // Floating point exception.
        0b101000 | 0b101100 => Some(SIGFPE),

        _ => None,
    }
}