refactor(adapter): split trap/page_table/smp/entry by concern; trim comments

crates/adapter-riscv/src/main.rs

@@ -5,6 +5,7 @@ mod board;
 mod boot;
 mod boot_fs;
 mod devices;
+mod entry;
 mod hw;
 mod kernel_cell;
 mod mmu;
@@ -12,7 +13,6 @@ mod platform;
 mod smp;
 mod trap;
 
-use core::arch::global_asm;
 use hw::uart::Uart;
 use kernel_cell::KernelCell;
 
@@ -28,92 +28,13 @@ pub fn kernel_ptr() -> *mut kernel::Kernel<platform::RiscVPlatform> {
     KERNEL.as_ptr()
 }
 
-// Firmware enters `_start` (and SBI starts other harts at
-// `_secondary_start`) at the physical load address with the MMU off and
-// the hart id in a0, but the kernel is linked in the upper half. Using
-// only PC-relative code, the stub turns on `boot_page_table`, which maps
-// RAM twice (at its physical address, just so the next instruction still
-// exists, and in the upper half) plus the MMIO window high, then jumps to
-// its own high address and takes the hart's kernel stack. The kernel then
-// switches every hart to the real table, which maps nothing low.
-global_asm!(
-    r#"
-.section .text.entry
-.globl _start
-_start:
-    lla t2, start_high_address
-    j 1f
-.globl _secondary_start
-_secondary_start:
-    lla t2, secondary_high_address
-1:
-    li t0, 8                # smp::MAX_HARTS
-    bgeu a0, t0, spin
-    mv s0, a0
-    lla t0, boot_page_table
-    srli t0, t0, 12
-    li t1, 8 << 60
-    or t0, t0, t1
-    csrw satp, t0
-    sfence.vma
-    ld t0, 0(t2)
-    jr t0
-
-# sp = _stacks_start + (hart + 1) * smp::STACK_SLOT
-start_high:
-    call hart_stack
-    mv a0, s0
-    call kmain
-    j spin
-secondary_high:
-    call hart_stack
-    mv a0, s0
-    call kmain_secondary
-    j spin
-hart_stack:
-    lla sp, _stacks_start
-    addi t0, s0, 1
-    li t1, 0x81000
-    mul t0, t0, t1
-    add sp, sp, t0
-    ret
-spin:
-    wfi
-    j spin
-
-.pushsection .rodata
-.balign 8
-start_high_address:
-    .quad start_high
-secondary_high_address:
-    .quad secondary_high
-.popsection
-
-# Sv39 root of 1 GiB leaves; an entry is (PA >> 12) << 10 | flags, with
-# flags V|R|W|A|D = 0xc7, plus X = 0xcf.
-.pushsection .data
-.balign 4096
-boot_page_table:
-    .quad 0
-    .quad 0
-    .quad 0x200000cf    # [2]   0x8000_0000 -> RAM, for the jump only
-    .fill 253, 8, 0
-    .quad 0x000000c7    # [256] PHYS_OFFSET + 0 -> MMIO
-    .quad 0
-    .quad 0x200000cf    # [258] PHYS_OFFSET + 0x8000_0000 -> RAM
-    .fill 253, 8, 0
-.popsection
-"#
-);
-
 #[unsafe(no_mangle)]
 extern "C" fn kmain(hart: usize) -> ! {
     let uart = Uart::new();
     uart.write_str("k-os: booted on RISC-V\n");
 
     boot::hardware::init(&uart, hart);
-    // Held until the boot hart first enters userspace; harts started
-    // below wait for it. Not before init: zeroing .bss resets the lock.
+    // Not before init: zeroing .bss resets the lock.
     smp::lock();
     let mut blk =
         boot::hardware::probe_block_device(&uart).unwrap_or_else(|| halt(&uart, "no block device"));
@@ -129,7 +50,7 @@ extern "C" fn kmain(hart: usize) -> ! {
         .unwrap_or_else(|_| halt(&uart, "board registration failed"));
     devices::display_quota(&uart, display.pid);
     boot::caps::grant_all(&uart, init.pid, storage.pid, display.pid, input.pid);
-    // After grant_all, so the slots init already relies on stay put.
+    // After grant_all: init already relies on those slots.
     let mut placed = [None; board::BOARD_DEVICES];
     let system_control = kern_mut()
         .grant_boot_authority(init.pid, &board, &mut placed)