mirror of
https://github.com/saymrwulf/xous-core.git
synced 2026-11-14 08:03:34 +00:00
125 lines
4.2 KiB
Rust
125 lines
4.2 KiB
Rust
use core::arch::asm;
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use crate::platform;
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// Assembly stubs for entering into the loader, and exiting it.
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// Note: inline constants are not yet stable in Rust: https://github.com/rust-lang/rust/pull/104087
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#[link_section = ".text.init"]
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#[export_name = "_start"]
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pub extern "C" fn _start(_kernel_args: usize, loader_sig: usize) {
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#[cfg(any(feature="precursor", feature="renode"))]
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let _kernel_args = _kernel_args;
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#[cfg(any(feature="cramium-soc", feature="cramium-fpga"))]
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let _kernel_args = _start as *const usize as usize + platform::KERNEL_OFFSET;
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unsafe {
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asm! (
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"li t0, 0xffffffff",
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"csrw mideleg, t0",
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"csrw medeleg, t0",
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// decorate our stack area with a canary pattern
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"li t1, 0xACE0BACE",
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"mv t0, {stack_limit}",
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"mv t2, {ram_top}",
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"100:", // fillstack
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"sw t1, 0(t0)",
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"addi t0, t0, 4",
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"bltu t0, t2, 100b",
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// Place the stack pointer at the end of RAM
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"mv sp, {ram_top}",
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// Install a machine mode trap handler
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"la t0, abort",
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"csrw mtvec, t0",
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// this forces a0/a1 to be "used" and thus not allocated for other parameters passed in
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"mv a0, {kernel_args}",
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"mv a1, {loader_sig}",
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// Start Rust
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"j rust_entry",
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kernel_args = in(reg) _kernel_args,
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loader_sig = in(reg) loader_sig,
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ram_top = in(reg) (platform::RAM_BASE + platform::RAM_SIZE),
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// On Precursor - 0x40FFE01C: currently allowed stack extent - 8k - (7 words). 7 words are for kernel backup args - see bootloader in betrusted-soc
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stack_limit = in(reg) (platform::RAM_BASE + platform::RAM_SIZE - 8192 + 7 * core::mem::size_of::<usize>()),
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options(noreturn)
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);
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}
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}
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#[link_section = ".text.init"]
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#[export_name = "abort"]
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/// This is only used in debug mode
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pub extern "C" fn abort() {
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unsafe {
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asm! (
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"300:", // abort
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"j 300b",
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options(noreturn)
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);
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}
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}
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#[inline(never)]
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#[export_name = "start_kernel"]
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pub extern "C" fn start_kernel(
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args: usize,
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ss: usize,
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rpt: usize,
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satp: usize,
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entrypoint: usize,
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stack: usize,
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debug_: bool,
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resume_: bool,
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) -> ! {
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let debug: usize = if debug_ { 1 } else { 0 };
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let resume: usize = if resume_ { 1 } else { 0 };
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unsafe {
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asm! (
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// these generate redundant mv's but it ensures that the arguments are marked as used
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"mv a0, {args}",
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"mv a1, {ss}",
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"mv a2, {rpt}",
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"mv a7, {resume}",
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// Delegate as much as we can supervisor mode
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"li t0, 0xffffffff",
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"csrw mideleg, t0",
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"csrw medeleg, t0",
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// Return to Supervisor mode (1 << 11) when we call `reti`.
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// Disable interrupts (0 << 5)
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"li t0, (1 << 11) | (0 << 5)",
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// If arg6 is "true", also set mstatus.SUM to allow the kernel
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// to access userspace memory.
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"mv a6, {debug}",
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"andi a6, a6, 1",
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"slli a6, a6, 18",
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"or t0, t0, a6",
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"csrw mstatus, t0",
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// Enable the MMU (once we issue `mret`) and flush the cache
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"csrw satp, {satp}",
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"sfence.vma",
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// Return to the address pointed to by $a4
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"csrw mepc, {entrypoint}",
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// Reposition the stack at the offset passed by $a5
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"mv sp, {stack}",
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// Issue the return, which will jump to $mepc in Supervisor mode
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"mret",
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args = in(reg) args,
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ss = in(reg) ss,
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rpt = in(reg) rpt,
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satp = in(reg) satp,
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entrypoint = in(reg) entrypoint,
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stack = in(reg) stack,
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debug = in(reg) debug,
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resume = in(reg) resume,
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options(noreturn)
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);
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}
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}
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