Add simple bootloader for mipsel

Signed-off-by: Harry Chen <i@harrychen.xyz>

bootloader/Makefile

@@ -13,6 +13,8 @@ else ifeq ($(arch), riscv32)
 prefix := riscv64-unknown-elf-
 else ifeq ($(arch), riscv64)
 prefix := riscv64-unknown-elf-
+else ifeq ($(arch), mipsel)
+prefix := mipsel-linux-gnu-
 else ifeq ($(arch), aarch64)
 prefix ?= aarch64-none-elf-
 ifeq (,$(shell which $(prefix)ld))
@@ -30,6 +32,7 @@ strip := $(prefix)strip
 
 export CC = $(cc)
 export PAYLOAD = $(payload)
+export DTB = $(dtb)
 
 build_args := --target=targets/$(arch).json
 ifeq ($(mode), release)

bootloader/build.rs

@@ -10,14 +10,22 @@ fn main() {
     }
 }
 
+/// include payload and dtb in sections of asm
 fn gen_payload_asm() -> Result<std::path::PathBuf> {
     let out_dir = std::env::var("OUT_DIR").unwrap();
     let payload = std::env::var("PAYLOAD").unwrap();
+    let dtb = std::env::var("DTB").unwrap();
 
     if !Path::new(&payload).is_file() {
         panic!("Kernel payload `{}` not found", payload)
     }
 
+    let mut has_dtb = true;
+
+    if !Path::new(&dtb).is_file() {
+        has_dtb = false;
+    }
+
     let file_path = Path::new(&out_dir).join("payload.S");
     let mut f = File::create(&file_path).unwrap();
 
@@ -36,5 +44,19 @@ _kernel_payload_end:
     println!("cargo:rerun-if-changed={}", payload);
     println!("cargo:rerun-if-env-changed=PAYLOAD");
 
+    if has_dtb {
+        write!(f, r#"
+    .section .dtb,"a"
+    .align 12
+    .global _dtb_start, _dtb_end
+_dtb_start:
+    .incbin "{}"
+_dtb_end:
+    "#, dtb)?;
+        println!("{:x?} {:x?}", dtb, file_path);
+        println!("cargo:rerun-if-changed={}", dtb);
+        println!("cargo:rerun-if-env-changed=DTB");
+    }
+
     Ok(file_path)
 }

bootloader/src/arch/mipsel/boot.S

@@ -0,0 +1,20 @@
+.section .text.boot
+.globl _start
+
+_start:
+    # read cpu affinity, start core 0, halt the rest
+    mfc0    $8, $15, 1
+    beqz    $8, setup
+    andi    $8, $8, 0x3ff # use bits 11 ~ 0
+
+halt:
+    # core affinity != 0, halt it
+    b       halt
+    nop
+
+setup:
+    # put the bootstack at 8MB offset of physical mem
+    la     $29, 0x80800000 # $sp
+    la     $28, _gp        # $gp
+    b      boot_main
+    nop

bootloader/src/arch/mipsel/boot.ld

@@ -0,0 +1,41 @@
+ENTRY(_start)
+
+SECTIONS {
+
+  /* MIPS entry point after cold reset */
+  . = 0xBFC00000;
+
+  .text : {
+    KEEP(*(.text.boot)) /* from boot.S */
+    *(.text .text.* .gnu.linkonce.t*)
+    . = ALIGN(4K);
+  }
+
+  .rodata : {
+    *(.rodata .rodata.* .gnu.linkonce.r*)
+    . = ALIGN(4K);
+  }
+
+  .data : {
+    *(.data .data.* .gnu.linkonce.d*)
+    . = ALIGN(4K);
+  }
+
+  .bss : {
+    _sbss = .;
+    *(.bss .bss.*)
+    *(COMMON)
+    . = ALIGN(4K);
+    _ebss = .;
+  }
+
+  .payload : {
+    *(.payload)
+  }
+
+  .dtb : {
+    *(.dtb)
+  }
+
+  /DISCARD/ : { *(.comment) *(.gnu*) *(.note*) *(.eh_frame*) }
+}

bootloader/src/arch/mipsel/mod.rs

@@ -0,0 +1,34 @@
+use core::ptr;
+use fixedvec::FixedVec;
+use xmas_elf::program::{ProgramHeader32, Type};
+
+const KERNEL_OFFSET: u32 = 0x80000000;
+
+global_asm!(include_str!("boot.S"));
+
+pub fn copy_kernel(kernel_start: usize, segments: &FixedVec<ProgramHeader32>) {
+    // reverse program headers to avoid overlapping in memory copying
+    let mut space = alloc_stack!([ProgramHeader32; 32]);
+    let mut rev_segments = FixedVec::new(&mut space);
+    for i in (0..segments.len()).rev() {
+        rev_segments.push(segments[i]).unwrap();
+    }
+
+    for segment in &rev_segments {
+        if segment.get_type() != Ok(Type::Load) {
+            continue;
+        }
+        let virt_addr = segment.virtual_addr;
+        let offset = segment.offset;
+        let file_size = segment.file_size;
+        let mem_size = segment.mem_size;
+
+        unsafe {
+            let src = (kernel_start as u32 + offset) as *const u8;
+            let dst = virt_addr.wrapping_sub(KERNEL_OFFSET) as *mut u8;
+            ptr::copy(src, dst, file_size as usize);
+            ptr::write_bytes(dst.offset(file_size as isize), 0, (mem_size - file_size) as usize);
+        }
+    }
+
+}

bootloader/src/main.rs

@@ -12,13 +12,18 @@ use core::slice;
 use fixedvec::FixedVec;
 use xmas_elf::{
     header,
-    program::{ProgramHeader, ProgramHeader64},
+    program::{ProgramHeader, ProgramHeader32, ProgramHeader64},
     ElfFile,
 };
 
 #[cfg(target_arch = "aarch64")]
 #[path = "arch/aarch64/mod.rs"]
 pub mod arch;
+
+#[cfg(target_arch = "mips")]
+#[path = "arch/mipsel/mod.rs"]
+pub mod arch;
+
 pub mod lang_items;
 
 extern "C" {
@@ -26,8 +31,15 @@ extern "C" {
     fn _kernel_payload_end();
 }
 
+#[cfg(target_arch = "mips")]
+extern "C" {
+    fn _dtb_start();
+    fn _dtb_end();
+}
+
 /// The entry point of bootloader
-#[no_mangle] // don't mangle the name of this function
+#[cfg(target_arch = "aarch64")]
+#[no_mangle]
 pub extern "C" fn boot_main() -> ! {
     let kernel_size = _kernel_payload_end as usize - _kernel_payload_start as usize;
     let kernel = unsafe { slice::from_raw_parts(_kernel_payload_start as *const u8, kernel_size) };
@@ -54,3 +66,33 @@ pub extern "C" fn boot_main() -> ! {
 
     loop {}
 }
+
+
+#[cfg(target_arch = "mips")]
+#[no_mangle]
+pub extern "C" fn boot_main() -> ! {
+    let kernel_size = _kernel_payload_end as usize - _kernel_payload_start as usize;
+    let kernel = unsafe { slice::from_raw_parts(_kernel_payload_start as *const u8, kernel_size) };
+    let kernel_elf = ElfFile::new(kernel).unwrap();
+    header::sanity_check(&kernel_elf).unwrap();
+
+    let mut preallocated_space = alloc_stack!([ProgramHeader32; 32]);
+    let mut segments = FixedVec::new(&mut preallocated_space);
+
+    for program_header in kernel_elf.program_iter() {
+        match program_header {
+            ProgramHeader::Ph32(header) => segments
+                .push(*header)
+                .expect("does not support more than 32 program segments"),
+            ProgramHeader::Ph64(_) => panic!("does not support 64 bit elf files"),
+        }
+    }
+
+    let entry = kernel_elf.header.pt2.entry_point() as u32;
+    let kernel_main: extern "C" fn(dtb: usize) = unsafe { transmute(entry) };
+
+    arch::copy_kernel(_kernel_payload_start as usize, &segments);
+    kernel_main(_dtb_start as usize);
+
+    loop {}
+}

bootloader/targets/mipsel.json

@@ -0,0 +1,36 @@
+{
+  "arch": "mips",
+  "cpu": "mips32r2",
+  "llvm-target": "mipsel-unknown-none",
+  "data-layout": "e-m:m-p:32:32-i8:8:32-i16:16:32-i64:64-n32-S64",
+  "target-endian": "little",
+  "target-pointer-width": "32",
+  "target-c-int-width": "32",
+  "os": "none",
+  "features": "+mips32r2",
+  "max-atomic-width": "32",
+  "linker": "rust-lld",
+  "linker-flavor": "ld.lld",
+  "pre-link-args": {
+    "ld.lld": [
+      "-Tsrc/arch/mipsel/boot.ld"
+    ]
+  },
+  "executables": true,
+  "panic-strategy": "abort",
+  "relocation-model": "static",
+  "abi-blacklist": [
+    "cdecl",
+    "stdcall",
+    "fastcall",
+    "vectorcall",
+    "thiscall",
+    "aapcs",
+    "win64",
+    "sysv64",
+    "ptx-kernel",
+    "msp430-interrupt",
+    "x86-interrupt"
+  ],
+  "eliminate-frame-pointer": false
+}