[英]Rust startup code for Raspberry Pi3 through use of inline assembly
我正在用Rust為Raspberry Pi 3寫一個裸機代碼,但是,我將代碼放置在0x80000
問題,因為它不是_start
函數。
編譯器針對AArch64架構設置,我使用LLD作為鏈接器。
# .cargo/config
[build]
target = "aarch64-unknown-none"
[target.aarch64-unknown-none]
rustflags = [
# uncomment to use rustc LLD linker
"-C", "link-arg=-Tlayout.ld",
"-C", "linker=lld-link",
"-Z", "linker-flavor=ld.lld",
]
啟動后要調用的第一個函數:(獲取核心ID並僅讓主線程繼續運行,其他線程停止;為主內存和初始化內存設置堆棧)
#[link_section = ".reset_vector"]
#[no_mangle]
pub extern "C" fn _start() -> !{
unsafe {
// Halt all cores but the primary
asm!(" mrs x1, mpidr_el1
and x1, x1, #3
cmp x1, #0
bne halt"::::"volatile");
// Setup stack pointer
asm!(" mov sp, #0x80000"::::"volatile");
}
init_runtime();
main();
loop{}
}
fn init_runtime() {
extern "C" {
static mut _sbss: u64;
static mut _ebss: u64;
static mut _sdata: u64;
static mut _edata: u64;
static _sidata: u64;
}
unsafe{
// Zero the BSS section in RAM
r0::zero_bss(&mut _sbss, &mut _ebss);
// Copy variables in DATA section in FLASH to RAM
r0::init_data(&mut _sdata, &mut _edata, &_sidata);
}
}
停止除主要節點之外的核心的功能:
#[no_mangle]
pub fn halt() {
unsafe {asm!("wfe"::::"volatile");}
}
我正在使用r0
板條箱初始化內存:
fn init_runtime() {
extern "C" {
static mut _sbss: u64;
static mut _ebss: u64;
static mut _sdata: u64;
static mut _edata: u64;
static _sidata: u64;
}
unsafe{
// Zero the BSS section in RAM
r0::zero_bss(&mut _sbss, &mut _ebss);
// Copy variables in DATA section in FLASH to RAM
r0::init_data(&mut _sdata, &mut _edata, &_sidata);
}
}
最后是鏈接描述文件:
ENTRY(_start)
SECTIONS {
. = 0x80000;
.text : {
KEEP(*(.reset_vector));
__reset_vector = ABSOLUTE(.);
*(.text .text.* .gnu.linkonce.t*)
}
.rodata : {
*(.rodata .rodata.* .gnu.linkonce.r*)
}
.data : {
_sdata = .;
*(.data .data.* .gnu.linkonce.d*)
_edata = ALIGN(8);
}
.bss (NOLOAD) : {
. = ALIGN(32);
_bss = .;
*(.bss .bss.*)
*(COMMON)
_ebss = ALIGN(8);
}
__bss_length = (__bss_end - __bss_start);
/DISCARD/ : { *(.comment) *(.gnu*) *(.note*) *(.eh_frame*) }
}
這是反匯編:
(gdb) disassemble 0x0000000000080000, 0x000000000008035c
Dump of assembler code from 0x80000 to 0x8035c:
=> 0x0000000000080000 <core::mem::uninitialized+0>: sub sp, sp, #0x10
0x0000000000080004 <core::mem::uninitialized+4>: ldr x0, [sp, #8]
0x0000000000080008 <core::mem::uninitialized+8>: str x0, [sp]
0x000000000008000c <core::mem::uninitialized+12>: ldr x0, [sp]
0x0000000000080010 <core::mem::uninitialized+16>: add sp, sp, #0x10
0x0000000000080014 <core::mem::uninitialized+20>: ret
來自函數_start的指令需要放置在@ 0x80000上,但這不是事實,因為存在core::mem::uninitialized
的指令。
如何修改鏈接描述文件,使mrs x1, mpidr_el1
成為要執行的第一條指令?
經過漫長的夜晚奮斗,我想出了辦法。
首先在鏈接器中創建一個新部分:
ENTRY(reset)
SECTIONS {
. = 0x80000;
.reset : {
KEEP(*(.reset))
. = ALIGN(8);
}
.text : {
*(.text .text.* .gnu.linkonce.t*)
}
...
並修改代碼:
#[link_section=".reset"]
#[no_mangle]
#[naked]
pub extern "C" fn reset () {
unsafe {
// Halt all cores but the primary and set stack pointer
asm!(" mrs x1, mpidr_el1
and x1, x1, #3
cmp x1, #0
bne halt
mov sp, #0x80000
b init
"::::"volatile");
}
}
其余的:
#[naked]
#[no_mangle]
pub fn init() {
extern "C" {
static mut _sbss: u64;
static mut _ebss: u64;
static mut _sdata: u64;
static mut _edata: u64;
static _sidata: u64;
}
unsafe{
// Zero the BSS section in RAM
r0::zero_bss(&mut _sbss, &mut _ebss);
// Copy variables in DATA section in FLASH to RAM
r0::init_data(&mut _sdata, &mut _edata, &_sidata);
}
extern "Rust" {
fn main() -> !;
}
unsafe { main(); }
}
通過分割代碼,復位中的初始化保持在0x80000
。
Disassembly of section .reset:
0000000000080000 <reset>:
80000: d53800a1 mrs x1, mpidr_el1
80004: 92400421 and x1, x1, #0x3
80008: f100003f cmp x1, #0x0
8000c: 54001481 b.ne 8029c <halt> // b.any
80010: b26d03ff mov sp, #0x80000 // #524288
80014: 1400008d b 80248 <init>
80018: d65f03c0 ret
8001c: 00000000 .inst 0x00000000 ; undefined
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