feat: add trampoline definition

Cargo.lock

@@ -14,6 +14,15 @@ version = "1.3.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "bef38d45163c2f1dde094a7dfd33ccf595c92905c8f8f4fdc18d06fb1037718a"
 
+[[package]]
+name = "lazy_static"
+version = "1.4.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e2abad23fbc42b3700f2f279844dc832adb2b2eb069b2df918f455c4e18cc646"
+dependencies = [
+ "spin",
+]
+
 [[package]]
 name = "log"
 version = "0.4.20"
@@ -53,6 +62,12 @@ dependencies = [
  "static_assertions",
 ]
 
+[[package]]
+name = "spin"
+version = "0.5.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6e63cff320ae2c57904679ba7cb63280a3dc4613885beafb148ee7bf9aa9042d"
+
 [[package]]
 name = "static_assertions"
 version = "1.1.0"
@@ -63,8 +78,10 @@ checksum = "a2eb9349b6444b326872e140eb1cf5e7c522154d69e7a0ffb0fb81c06b37543f"
 name = "tiny_os"
 version = "0.1.0"
 dependencies = [
+ "lazy_static",
  "log",
  "sbi-rt",
+ "static_assertions",
  "uart_16550",
 ]
 

Cargo.toml

@@ -8,6 +8,7 @@ edition = "2021"
 [features]
 default = ["arch_riscv64", "board_virt"]
 arch_riscv64 = []
+arch_riscv32 = []
 arch_arm = []
 arch_x86 = []
 board_default = []
@@ -21,6 +22,8 @@ panic = "abort"
 panic = "abort"
 
 [dependencies]
-sbi-rt = { version = "0.0.2", features = ["legacy"] }
-uart_16550 = "0.3"
+lazy_static = { version = "1.4.0", features = ["spin_no_std"] }
 log = "0.4"
+sbi-rt = { version = "0.0.2", features = ["legacy"] }
+static_assertions = "1.1.0"
+uart_16550 = "0.3"

build.rs

@@ -8,12 +8,13 @@ fn main() {
 
     const TARGET_CONFIGURATIONS: &[TargetConfiguration] = &[TargetConfiguration {
         target: "riscv64",
-        lds: "src/arch/riscv/boot/linker64.ld",
+        lds: "src/arch/riscv/linker64.ld",
     }];
 
     let target = std::env::var("TARGET").unwrap();
     for cfg in TARGET_CONFIGURATIONS {
         if target.starts_with(cfg.target) {
+            println!("cargo:rerun-if-changed={}", cfg.lds);
             println!("cargo:rustc-link-arg=-T{}", cfg.lds);
             return;
         }

src/arch/riscv/asm/trap32.S

@@ -0,0 +1,123 @@
+.section .trampoline_section
+
+.global trampoline
+trampoline:
+
+.align 4
+
+.global __user2kernel
+__user2kernel:
+	# load trapframe
+	csrw	sscratch, a0	# save a0, will be saved later
+	li	a0, {TRAPFRAME}	# TRAPFRAME will be mapped to the same virtual address
+
+	# save GPRs
+	sd	ra,    0(a0)
+	sd	sp,    4(a0)
+	sd	gp,    8(a0)
+	sd	tp,   12(a0)
+	sd	t0,   16(a0)
+	sd	t1,   20(a0)
+	sd	t2,   24(a0)
+	sd	s0,   28(a0)
+	sd	s1,   32(a0)
+	#sd	a0,   36(a0)
+	sd	a1,   40(a0)
+	sd	a2,   44(a0)
+	sd	a3,   48(a0)
+	sd	a4,   52(a0)
+	sd	a5,   56(a0)
+	sd	a6,   60(a0)
+	sd	a7,   64(a0)
+	sd	s2,   68(a0)
+	sd	s3,   72(a0)
+	sd	s4,   76(a0)
+	sd	s5,   80(a0)
+	sd	s6,   84(a0)
+	sd	s7,   88(a0)
+	sd	s8,   92(a0)
+	sd	s9,   96(a0)
+	sd	s10, 100(a0)
+	sd	s11, 104(a0)
+	sd	t3,  108(a0)
+	sd	t4,  112(a0)
+	sd	t5,  116(a0)
+	sd	t6,  120(a0)
+
+	# save a0
+	csrr	t0, sscratch
+	sd	t0, 36(a0)
+
+	# save user epc / sstatus
+	csrr	t0, sepc
+	csrr	t1, sstatus
+	sd	t0, 124(a0)
+	sd	t1, 128(a0)
+
+	# restore kernel env
+	ld	sp, 132(a0)	# kernel sp
+	ld	tp, 136(a0)	# kernel tp
+	ld	t0, 140(a0)	# trap handler
+	ld	t1, 144(a0)	# page table
+
+	# load kernel page table
+	sfence.vma	zero, zero
+	csrw		satp, t1
+	sfence.vma	zero, zero
+
+	# jump to trap handler
+	jr	t0
+
+.global __kernel2user
+__kernel2user:
+	# restore user page table (a0)
+	sfence.vma	zero, zero
+	csrw		satp, a0
+	sfence.vma	zero, zero
+
+	li	a0, {TRAPFRAME}
+
+	# restore user epc / sstatus
+	ld	t0, 124(a0)
+	ld	t1, 128(a0)
+	csrw	sepc, t0
+	csrw	sstatus, t1
+
+	# restore GPRs
+	ld	ra,    0(a0)
+	ld	sp,    4(a0)
+	ld	gp,    8(a0)
+	ld	tp,   12(a0)
+	ld	t0,   16(a0)
+	ld	t1,   20(a0)
+	ld	t2,   24(a0)
+	ld	s0,   28(a0)
+	ld	s1,   32(a0)
+	#ld	a0,   36(a0)
+	ld	a1,   40(a0)
+	ld	a2,   44(a0)
+	ld	a3,   48(a0)
+	ld	a4,   52(a0)
+	ld	a5,   56(a0)
+	ld	a6,   60(a0)
+	ld	a7,   64(a0)
+	ld	s2,   68(a0)
+	ld	s3,   72(a0)
+	ld	s4,   76(a0)
+	ld	s5,   80(a0)
+	ld	s6,   84(a0)
+	ld	s7,   88(a0)
+	ld	s8,   92(a0)
+	ld	s9,   96(a0)
+	ld	s10, 100(a0)
+	ld	s11, 104(a0)
+	ld	t3,  108(a0)
+	ld	t4,  112(a0)
+	ld	t5,  116(a0)
+	ld	t6,  120(a0)
+	ld	a0,   36(a0)
+
+	# go back to usermode
+	sret
+
+# vim:set ts=8 noexpandtab:

src/arch/riscv/asm/trap64.S

@@ -0,0 +1,123 @@
+.section .trampoline_section
+
+.global trampoline
+trampoline:
+
+.align 4
+
+.global __user2kernel
+__user2kernel:
+	# load trapframe
+	csrw	sscratch, a0	# save a0, will be saved later
+	li	a0, {TRAPFRAME}	# TRAPFRAME will be mapped to the same virtual address
+
+	# save GPRs
+	sd	ra,    0(a0)
+	sd	sp,    8(a0)
+	sd	gp,   16(a0)
+	sd	tp,   24(a0)
+	sd	t0,   32(a0)
+	sd	t1,   40(a0)
+	sd	t2,   48(a0)
+	sd	s0,   56(a0)
+	sd	s1,   64(a0)
+	#sd	a0,   72(a0)
+	sd	a1,   80(a0)
+	sd	a2,   88(a0)
+	sd	a3,   96(a0)
+	sd	a4,  104(a0)
+	sd	a5,  112(a0)
+	sd	a6,  120(a0)
+	sd	a7,  128(a0)
+	sd	s2,  136(a0)
+	sd	s3,  144(a0)
+	sd	s4,  152(a0)
+	sd	s5,  160(a0)
+	sd	s6,  168(a0)
+	sd	s7,  176(a0)
+	sd	s8,  184(a0)
+	sd	s9,  192(a0)
+	sd	s10, 200(a0)
+	sd	s11, 208(a0)
+	sd	t3,  216(a0)
+	sd	t4,  224(a0)
+	sd	t5,  232(a0)
+	sd	t6,  240(a0)
+
+	# save a0
+	csrr	t0, sscratch
+	sd	t0, 72(a0)
+
+	# save user epc / sstatus
+	csrr	t0, sepc
+	csrr	t1, sstatus
+	sd	t0, 248(a0)
+	sd	t1, 256(a0)
+
+	# restore kernel env
+	ld	sp, 264(a0)	# kernel sp
+	ld	tp, 272(a0)	# kernel tp
+	ld	t0, 280(a0)	# trap handler
+	ld	t1, 288(a0)	# page table
+
+	# load kernel page table
+	sfence.vma	zero, zero
+	csrw		satp, t1
+	sfence.vma	zero, zero
+
+	# jump to trap handler
+	jr	t0
+
+.global __kernel2user
+__kernel2user:
+	# restore user page table (a0)
+	sfence.vma	zero, zero
+	csrw		satp, a0
+	sfence.vma	zero, zero
+
+	li	a0, {TRAPFRAME}
+
+	# restore user epc / sstatus
+	ld	t0, 248(a0)
+	ld	t1, 256(a0)
+	csrw	sepc, t0
+	csrw	sstatus, t1
+
+	# restore GPRs
+	ld	ra,    0(a0)
+	ld	sp,    8(a0)
+	ld	gp,   16(a0)
+	ld	tp,   24(a0)
+	ld	t0,   32(a0)
+	ld	t1,   40(a0)
+	ld	t2,   48(a0)
+	ld	s0,   56(a0)
+	ld	s1,   64(a0)
+	#ld	a0,   72(a0)
+	ld	a1,   80(a0)
+	ld	a2,   88(a0)
+	ld	a3,   96(a0)
+	ld	a4,  104(a0)
+	ld	a5,  112(a0)
+	ld	a6,  120(a0)
+	ld	a7,  128(a0)
+	ld	s2,  136(a0)
+	ld	s3,  144(a0)
+	ld	s4,  152(a0)
+	ld	s5,  160(a0)
+	ld	s6,  168(a0)
+	ld	s7,  176(a0)
+	ld	s8,  184(a0)
+	ld	s9,  192(a0)
+	ld	s10, 200(a0)
+	ld	s11, 208(a0)
+	ld	t3,  216(a0)
+	ld	t4,  224(a0)
+	ld	t5,  232(a0)
+	ld	t6,  240(a0)
+	ld	a0,   72(a0)
+
+	# go back to usermode
+	sret
+
+# vim:set ts=8 noexpandtab:

src/arch/riscv/layout.rs

@@ -0,0 +1,2 @@
+// TODO: currently a dummy value, figure out our memory layout
+pub const TRAPFRAME: usize = 0x8000_0000;

src/arch/riscv/linker64.ld

@@ -14,6 +14,15 @@ SECTIONS {
         __text_start = .;
         *(.text.entry)
         *(.text .text.*)
+
+        . = ALIGN(0x1000);
+        __trampoline_start = .;
+        *(.trampoline_section)
+        . = ALIGN(0x1000);
+        __trampoline_end = .;
+
+        ASSERT(__trampoline_end - __trampoline_start == 0x1000, "trampoline larger than one page");
+
         __text_end = .;
     } > DRAM
 

src/arch/riscv/mod.rs

@@ -2,6 +2,9 @@
 #[path = "board/virt/mod.rs"]
 mod board;
 
+mod layout;
+
 pub mod entry;
 pub mod io;
 pub mod lowlevel;
+pub mod trap;

src/arch/riscv/trap.rs

@@ -0,0 +1,37 @@
+use lazy_static::lazy_static;
+#[cfg(feature = "arch_riscv64")]
+core::arch::global_asm!(
+    include_str!("./asm/trap64.S"),
+    TRAPFRAME = const super::layout::TRAPFRAME
+);
+
+#[cfg(feature = "arch_riscv32")]
+core::arch::global_asm!(
+    include_str!("./asm/trap32.S"),
+    TRAPFRAME = const super::layout::TRAPFRAME
+);
+
+extern "C" {
+    pub fn __user2kernel();
+    pub fn __kernel2user(ctx: *mut TrapContext);
+}
+
+// TODO: remove this when we have a real context switch
+lazy_static! {
+    pub static ref __DUMMY: usize = unsafe {
+        __user2kernel();
+        __kernel2user(core::ptr::null_mut());
+        42
+    };
+}
+
+#[repr(C)]
+pub struct TrapContext {
+    pub gprs: [usize; 31],   // GPRs exclude zero
+    pub user_sepc: usize,    // 248/124 user program counter
+    pub user_sstatus: usize, // 256/128 user status register
+    pub kernel_sp: usize,    // 264/132 kernel stack pointer
+    pub kernel_tp: usize,    // 272/136 kernel tp
+    pub kernel_trap: usize,  // 280/140 kernel trap handler
+    pub kernel_satp: usize,  // 288/144 kernel page table
+}

src/lib.rs

@@ -5,6 +5,8 @@
 #![feature(fmt_internals)]
 #![feature(stmt_expr_attributes)]
 
+extern crate static_assertions;
+
 // arch
 pub mod arch;