Trim unnecessary unsafe blocks

build.rs

@@ -2,7 +2,7 @@
 
 fn main() {
   // Tell ld to use linker script.
-  println!("cargo::rustc-link-arg=-Tsrc/script.ld");
+  println!("cargo::rustc-link-arg=-Tsrc/script.lds");
   // Don't do any magic linker stuff.
   println!("cargo::rustc-link-arg=--omagic");
 }

src/entry.rs

@@ -1,16 +1,75 @@
-use crate::abort;
+// src/entry.rs
+#[no_mangle]
+#[link_section = ".text.init"]
+unsafe extern "C" fn _entry() {
+    use core::arch::asm;
+    // let id = riscv::register::mhartid::read();
+    // write_tp(&id);
+    // TODO set up stack for all harts
+    // TODO set up CSRs for all harts
+    // if id != 0 { abort(); }
+
+    asm!(
+        /* Global pointer register `gp`
+        
+        Push current option stack to temporarily disable relaxation, load
+        _global_pointer symbol (provided by linker), then pop option stack.
+
+        Important to keep relaxation off for this instruction, so that
+        the instruction is emitted as:
+            1:
+                auipc gp, %pcrel_hi(_global_pointer)
+                addi gp, gp, %pcrel_lo(1b)"
+        instead of:
+                mv gp, gp
+        which would do nothing. */
+        ".option push",
+        ".option norelax",
+        "la gp, _global_pointer",
+        ".option pop",
+    );
+
+    riscv::register::satp::write(0);
 
-unsafe extern "C" fn _enter() {
     let id = riscv::register::mhartid::read();
-    write_tp(&id);
+    if id != 0 { crate::abort(); }
-    // TODO: set up stack for all harts
-    // TODO: set up CSRs for all harts
-    if id != 0 { abort(); }
 
-    // TODO: clear BSS
+    // Clear BSS section
-    // TODO: do hardware inits and wake other harts
+    asm!(
+        "la t0, _bss_start",
+        "la t1, _bss_end",
+        "bgeu t0, t1, 2f",
+    "1:",
+        "sb zero, 0(t0)",
+        "addi t0, t0, 1",
+        "bne t0, t1, 1b",
+
+    "2:",
+        "la sp, _stack_end",
+
+        "li t0, (0b11 << 11) | (1 << 13)",
+        "csrw mstatus, t0",
+        "csrw mie, x0",
+
+        "la t1, {kinit}",
+        "csrw mepc, t1",
+
+        "la ra, 2f",
+        "mret",
+    "2:",
+        kinit = sym kinit,
+    );
 }
 
+#[no_mangle]
+extern "C" fn kinit() {
+    use crate::uart;
+    uart::Device::new(0x1000_0000);
+}
+
+#[no_mangle]
+extern "C" fn kinit_hart() {}
+
 #[inline]
 unsafe fn write_tp(id: &usize) {
     use core::arch::asm;

src/heap.rs

@@ -14,23 +14,23 @@ static ALLOCATOR: LockedHeap = LockedHeap::empty();
 /// # Safety
 /// Must be called at most once.
 pub unsafe fn init() {
-    let heap_bottom;
+    let heap_start;
     let heap_size;
     // UNSAFE: This is fine, just loading some constants.
     unsafe {
         // using inline assembly is easier to access linker constants
         asm!(
-            "la {heap_bottom}, _kernel_heap_bottom",
+            "la {heap_start}, _heap_start",
-            "la {heap_size}, _kernel_heap_size",
+            "la {heap_size}, _heap_size",
-            heap_bottom = out(reg) heap_bottom,
+            heap_start = out(reg) heap_start,
             heap_size = out(reg) heap_size,
             options(nomem)
         )
     };
     println!(
         "Initialising kernel heap (bottom: {:#x}, size: {:#x})",
-        heap_bottom as usize, heap_size
+        heap_start as usize, heap_size
     );
     // UNSAFE: Fine to call at most once.
-    unsafe { ALLOCATOR.lock().init(heap_bottom, heap_size) };
+    unsafe { ALLOCATOR.lock().init(heap_start, heap_size) };
 }

src/main.rs

@@ -40,7 +40,7 @@ unsafe extern "C" fn _enter() -> ! {
         "csrw mideleg, t5", // delegate all machine interrupts
 
         // set the stack pointer
-        "la sp, _init_stack_top",
+        "la sp, _stack_end",
 
         // Make sure machine mode is set, and enable coarse interrupts
         "li t0, (0b11 << 11) | (1 << 7) | (1 << 3)",
@@ -96,7 +96,7 @@ extern "C" fn start() -> ! {
     // }
 
     // println!("This should not print because the console is not initialised.");
-    unsafe { uart::init_console(0x1000_0000) };
+    uart::init_console(0x1000_0000);
     println!("Hello, world!");
 
     // print current hartid

src/script.lds

@@ -1,4 +1,4 @@
-# src/script.ld
+/* src/script.lds */
 
 OUTPUT_ARCH("riscv")
 ENTRY(_enter)
@@ -17,18 +17,25 @@ SECTIONS {
   . = ORIGIN(ram); # start at 0x8000_0000 (DRAM)
 
   .text : { # put code first
+    PROVIDE(_text_start = .);
     *(.text.init) # start with anything in the .text.init section
     *(.text .text.*) # then put anything else in .text
+    PROVIDE(_text_end = .);
   } >ram AT>ram :text # put this section into the text segment
 
   PROVIDE(_global_pointer = .); # this is magic, google "linker relaxation"
 
   .rodata : { # next, read-only data
+    PROVIDE(_rodata_start = .);
     *(.rodata .rodata.*)
+    PROVIDE(_rodata_end = .);
   } >ram AT>ram :text # goes into the text segment as well (since instructions are generally read-only)
 
   .data : { # and the data section
+    . = ALIGN(4096);
+    PROVIDE(_data_start = .);
     *(.sdata .sdata.*) *(.data .data.*)
+    PROVIDE(_data_end = .);
   } >ram AT>ram :data # this will go into the data segment
 
   .bss :{ # finally, the BSS
@@ -37,10 +44,14 @@ SECTIONS {
     PROVIDE(_bss_end = .); # ... and one at the end
   } >ram AT>ram :bss # and this goes into the bss segment
 
-  . = ALIGN(16); # our stack needs to be 16-byte aligned, per the C calling convention
+  PROVIDE(_memory_start = ORIGIN(ram));
-  PROVIDE(_init_stack_top = . + 0x1000); # reserve 0x1000 bytes (4 kB) for the initialisation stack
 
-  PROVIDE(_kernel_heap_bottom = _init_stack_top); # allocate heap to remaining physical memory
+  . = ALIGN(16); # stack is 16-byte aligned, per the C calling convention
-  PROVIDE(_kernel_heap_top = ORIGIN(ram) + LENGTH(ram)); # top of heap is end of ram
+  PROVIDE(_stack_start = .);
-  PROVIDE(_kernel_heap_size = _kernel_heap_top - _kernel_heap_bottom); # capture size of heap
+  PROVIDE(_stack_end = _stack_start + 0x80000); # reserve 0x80000 bytes for the stack
+
+  PROVIDE(_memory_end = ORIGIN(ram) + LENGTH(ram));
+
+  PROVIDE(_heap_start = _stack_end); # allocate heap to remaining physical memory
+  PROVIDE(_heap_size = _memory_end - _heap_start); # capture size of heap
 }

src/uart.rs

@@ -14,7 +14,7 @@ impl Device {
     /// Create a new UART device.
     /// # Safety
     /// `base` must be the base address of a UART device.
-    pub unsafe fn new(base: usize) -> Self {
+    pub fn new(base: usize) -> Self {
         use core::ptr::write_volatile;
         let addr = base as *mut u8;
         // Set data size to 8 bits.
@@ -64,9 +64,9 @@ impl core::fmt::Write for Device {
 /// Initialise the UART debugging console.
 /// # Safety
 /// `base` must point to the base address of a UART device.
-pub unsafe fn init_console(base: usize) {
+pub fn init_console(base: usize) {
-    let mut console = CONSOLE.lock();
+    let mut console: spinning_top::lock_api::MutexGuard<spinning_top::RawSpinlock, Option<Device>> = CONSOLE.lock();
-    *console = Some(unsafe { Device::new(base) });
+    *console = Some(Device::new(base));
 }
 
 /// Prints a formatted string to the [CONSOLE].