prints hello world successfully

Cargo.toml

@@ -6,4 +6,7 @@ edition = "2021"
 [profile.dev]
 panic = "abort"
 
+[profile.release]
+panic = "abort"
+
 [dependencies]

scripts/start.sh

@@ -10,8 +10,8 @@ qemu-system-riscv64 \
     -machine virt \
     -bios none \
     -m 3G \
-    -d trace:exec_tb \
     -kernel "$KERNEL"
 
+    # -d trace:exec_tb \
     # -smp 3 \
     # -device virtio-blk-device,drive=x0,bus=virtio-mmio-bus.0 \

src/asm/entry.S

@@ -1,3 +1,18 @@
+.attribute arch, "rv64gc"
+
+.section .text.start
 .global _entry
 _entry:
+    la sp, stack0
+    li a0, 1024*8
+	csrr a1, mhartid
+    addi a1, a1, 1
+    mul a0, a0, a1
+    add sp, sp, a0
+
     call start
+
+.section .data
+.align 4
+stack0:
+    .space 8192 * 8 # 8 is NCPU in param.rs

src/ld/kernel.ld

@@ -6,12 +6,24 @@ SECTIONS {
     It seems that QEMU jumps to 0x80000000 after setting up memory, so we want
     our kernel code to begin here.
 
-    TODO: Is there an authoritative source that says that this is the address?
+    How to find this: Run QEMU using -d trace:exec_tb and see where the PC goes
-    How to test this: Run QEMU using -d trace:exec_tb and see where the PC goes
     */
     . = 0x80000000;
 
     .text : {
-        *(.text)
+        *(.text.start)
+        *(.text .text.*)
+    }
+
+    /*
+    Important: if this section was not included, the linker would put .rodata before .text
+    If the linker puts ANYTHING before .text, include it explicitly in the linker script AFTER
+    */
+    .rodata : {
+        *(.rodata .rodata.*)
+    }
+
+    .data : {
+        *(.data .data.*)
     }
 }

src/main.rs

@@ -1,23 +1,24 @@
 #![no_std]
 #![no_main]
 
-use core::panic::PanicInfo;
+use core::{arch::global_asm, panic::PanicInfo, ptr};
+
+global_asm!(include_str!("asm/entry.S"));
 
 #[panic_handler]
 fn panic_handler(_: &PanicInfo) -> ! {
     loop {}
 }
 
-static HELLO: &[u8] = b"Hello World!";
+const UART0: usize = 0x10000000;
+static HELLO: &[u8] = b"Hello World!\n";
 
-pub extern "C" fn start() -> ! {
+#[no_mangle]
-    let vga_buffer = 0xb8000 as *mut u8;
+pub unsafe extern "C" fn start() -> ! {
+    for c in HELLO.iter() {
+        while ptr::read_volatile((UART0 + 5) as *const u8) & (1 << 5) == 0 {}
 
-    for (i, &byte) in HELLO.iter().enumerate() {
+        ptr::write_volatile((UART0 + 0) as *mut u8, *c);
-        unsafe {
-            *vga_buffer.offset(i as isize * 2) = byte;
-            *vga_buffer.offset(i as isize * 2 + 1) = 0xb;
-        }
     }
 
     loop {}