Call Rust from assembly instead, relocate linker script
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@ -24,4 +24,5 @@ runner = """ qemu-system-riscv64
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-s
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-nographic
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-serial mon:stdio
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-bios """
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-bios none
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-kernel """
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2
build.rs
2
build.rs
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@ -2,7 +2,7 @@
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fn main() {
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// Tell ld to use linker script.
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println!("cargo::rustc-link-arg=-Tsrc/script.lds");
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println!("cargo::rustc-link-arg=-Tlds/kernel.lds");
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// Don't do any magic linker stuff.
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println!("cargo::rustc-link-arg=--omagic");
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}
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@ -1,7 +1,7 @@
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/* src/script.lds */
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OUTPUT_ARCH("riscv")
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ENTRY(_enter)
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ENTRY(_entry)
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MEMORY {
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ram (wxa) : ORIGIN = 0x80000000, LENGTH = 128M
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43
src/entry.S
Normal file
43
src/entry.S
Normal file
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@ -0,0 +1,43 @@
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# entry.S
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.option norvc
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.section .data
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.section .text.init
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.global _entry
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_entry:
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# Any hardware threads (hart) that are not bootstrapping
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# need to wait for an IPI
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csrr t0, mhartid
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bnez t0, 3f
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# SATP should be zero, but let's make sure
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csrw satp, zero
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.option push
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.option norelax
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la gp, _global_pointer
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.option pop
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li t5, 0xffff
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csrw medeleg, t5
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csrw mideleg, t5
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la sp, _stack_end
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li t0, (0b11 << 11) | (1 << 7) | (1 << 3)
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csrw mstatus, t0
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la t0, _bss_start
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la t1, _bss_end
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bgeu t0, t1, 2f
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1:
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sb zero, 0(t0)
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addi t0, t0, 1
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bne t0, t1, 1b
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2:
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j 4f
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3:
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wfi
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j 3b
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4:
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tail start
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10
src/entry.rs
10
src/entry.rs
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@ -56,16 +56,6 @@ unsafe extern "C" fn entry() {
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);
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}
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#[no_mangle]
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extern "C" fn start() {
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// TODO start (start for hart 0)
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}
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#[no_mangle]
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extern "C" fn hstart() {
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// TODO starth (start for other harts)
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}
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// TODO ...then kinit
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#[no_mangle]
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76
src/main.rs
76
src/main.rs
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@ -10,79 +10,9 @@ mod heap;
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mod trap;
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mod uart;
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#[naked]
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core::arch::global_asm!(include_str!("entry.S"));
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#[no_mangle]
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#[link_section = ".text.init"]
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unsafe extern "C" fn _enter() -> ! {
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// FIXME see if possible to replace this somehow...
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use core::arch::asm;
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asm!(
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// load hartid into `tp``
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// if hartid =/= 0, then jump to busy loop
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"csrr tp, mhartid",
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"bnez tp, 3f",
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// before we use the `la` pseudo-instruction for the first time,
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// we need to set `gp` (look up linker relaxation)
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".option push", // pushes the current option stack
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".option norelax", // disable relaxation so we can properly set `gp`
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// this instruction compiles to:
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// 1:
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// auipc gp, %pcrel_hi(_global_pointer)
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// addi gp, gp, %pcrel_lo(1b)
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// if relaxation were on, this would simply be `mv gp, gp` or `addi gp, gp, 0`
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"la gp, _global_pointer",
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".option pop", // pops the current option stack
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// delegate all traps to S-mode trap handler
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"li t5, 0xffff",
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"csrw medeleg, t5", // delegate all machine exceptions
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"csrw mideleg, t5", // delegate all machine interrupts
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// set the stack pointer
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"la sp, _stack_end",
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// Make sure machine mode is set, and enable coarse interrupts
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"li t0, (0b11 << 11) | (1 << 7) | (1 << 3)",
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"csrw mstatus, t0",
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// Set mtvec to the location of our trap handler function
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"la t1, {trap_vector}",
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"csrw mtvec, t1",
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// Set MSIE, MTIE, and MEIE on machine interrupt enable CSR:
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// (1 << 3) = MSIE to enable machine-/M-mode software interrupts
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// | (1 << 7) = MTIE to enable M-mode timer interrupts (disabled for now)
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// | (1 << 11) = MEIE to enable M-mode external interrupts
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"li t2, (1 << 3) | (1 << 11)",
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"csrw mie, t2",
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// clear the BSS
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"la t0, _bss_start",
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"la t1, _bss_end",
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"bgeu t0, t1, 2f",
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"1:",
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"sb zero, 0(t0)",
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"addi t0, t0, 1",
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"bne t0, t1, 1b",
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"2:",
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"j 4f",
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// BSS is clear!
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// busy loop if hartid =/= 0
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"3:",
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"wfi", // wait for interrupt (or nop)
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"j 3b",
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"4:",
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// "tail-call" to {start} (call without saving a return address)
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"tail {start}",
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start = sym start, // {start} refers to the function [start] below
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trap_vector = sym trap::trap_handler, // {trap_vector} refers to function [trap::trap_handler]
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options(noreturn) // we must handle "returning" from assembly
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);
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}
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extern "C" fn start() -> ! {
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// UNSAFE: Called exactly once, right here.
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unsafe { heap::init() };
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@ -125,4 +55,4 @@ extern "C" fn abort() -> ! {
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loop { riscv::asm::wfi(); }
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}
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// TODO unit testing
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// TODO unit testing
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