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Switched to using mret for trap

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This commit is contained in:
Stephen Marz 2019-10-14 16:14:22 -04:00
parent a10926df76
commit ccaf9b6a5c
6 changed files with 150 additions and 192 deletions
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47
risc_v/ch4/src/asm/boot.S
View File

@ -47,9 +47,14 @@ _start:
# to the very end of the stack range.
la sp, _stack_end
# Setting `mstatus` register:
# 0b11 << 11: Machine's previous protection mode is 3 (MPP=3).
# 0b01 << 11: Machine's previous protection mode is 2 (MPP=2).
li t0, 0b11 << 11
csrw mstatus, t0
# li t2, (1 << 1) | (1 << 5) | (1 << 9)
# li t2, 0xffff
# csrw mideleg, t2
li t3, 0xaaa
csrw mie, t3
# Machine's exception program counter (MEPC) is set to `kinit`.
la t1, kinit
csrw mepc, t1
@ -71,10 +76,10 @@ _start:
# 1 << 1 : Supervisor's interrupt-enable bit will be set to 1 after sret.
# We set the "previous" bits because the sret will write the current bits
# with the previous bits.
li t0, (1 << 8) | (1 << 5)
csrw sstatus, t0
li t0, (1 << 11)
csrw mstatus, t0
la t1, kmain
csrw sepc, t1
csrw mepc, t1
# Setting `mideleg` (machine interrupt delegate) register:
# 1 << 1 : Software interrupt delegated to supervisor mode
# 1 << 5 : Timer interrupt delegated to supervisor mode
@ -83,20 +88,19 @@ _start:
# cause an elevation to the machine privilege mode (mode 3).
# When we delegate, we're telling the CPU to only elevate to
# the supervisor privilege mode (mode 1)
li t2, (1 << 1) | (1 << 5) | (1 << 9)
csrw mideleg, t2
# Setting `sie` (supervisor interrupt enable) register:
# This register takes the same bits as mideleg
# 1 << 1 : Supervisor software interrupt enable (SSIE=1 [Enabled])
# 1 << 5 : Supervisor timer interrupt enable (STIE=1 [Enabled])
# 1 << 9 : Supervisor external interrupt enable (SEIE=1 [Enabled])
csrw sie, t2
# li t2, (1 << 1) | (1 << 5) | (1 << 9)
# csrw sie, t2
# Setting `stvec` (supervisor trap vector) register:
# Essentially this is a function pointer, but the last two bits can be 00 or 01
# 00 : All exceptions set pc to BASE
# 01 : Asynchronous interrupts set pc to BASE + 4 x scause
la t3, s_trap_vector
csrw stvec, t3
# la t3, s_trap
# csrw stvec, t3
# kinit() is required to return back the SATP value (including MODE) via a0
csrw satp, a0
# Force the CPU to take our SATP register.
@ -105,8 +109,10 @@ _start:
# it in memory, it will be the old table. So, sfence.vma will ensure that the MMU always
# grabs a fresh copy of the SATP register and associated tables.
sfence.vma
# ret
# call kmain
# sret will put us in supervisor mode and re-enable interrupts
sret
mret
3:
# Parked harts go here. We need to set these
@ -117,6 +123,27 @@ _start:
# where base address is 0x0200_0000 (MMIO CLINT base address)
# We only use additional harts to run user-space programs, although this may
# change.
la sp, _stack_end
li t0, 0x10000
csrr t1, mhartid
mul t0, t0, t1
sub sp, sp, t0
li t0, 0b01 << 11 | (1 << 5)
csrw mstatus, t0
li t3, 0xaaa
csrw mie, t3
# Machine's exception program counter (MEPC) is set to `kinit`.
la t1, 4f
csrw mepc, t1
# Machine's trap vector base address is set to `m_trap_vector`, for
# "machine" trap vector.
la t2, m_trap_vector
csrw mtvec, t2
# We use mret here so that the mstatus register is properly updated.
mret
4:
wfi
j 4b

177
risc_v/ch4/src/asm/trap.S
View File

@ -5,13 +5,14 @@
# 24 February 2019
.option norvc
.altmacro
.set NUM_GP_REGS, 34 # Number of registers per context
.set NUM_GP_REGS, 32 # Number of registers per context
.set NUM_FP_REGS, 32
.set REG_SIZE, 8 # Register size (in bytes)
.set MAX_CPUS, 8 # Maximum number of CPUs
.section .bss
.global _GLOBAL_CTX
.lcomm _GLOBAL_CTX, (NUM_FP_REGS + NUM_GP_REGS) * REG_SIZE
.lcomm _GLOBAL_CTX, (NUM_FP_REGS + NUM_GP_REGS) * REG_SIZE * MAX_CPUS
# Use macros for saving and restoring multiple registers
.macro save_gp i, basereg=t6
@ -39,21 +40,17 @@ m_trap_vector:
# base register for saving
csrw mscratch, t6
# Disable the MMU since we're switching.
csrr t6, satp
slli t6, t6, 4
srli t6, t6, 4
slli t6, t6, 1
srli t6, t6, 1
csrw satp, t6
# Disable interrupts
li t6, 1 << 3
csrrc zero, mstatus, t6
# Start saving the registers. We can't do much until the registers
# have been saved.
la t6, _GLOBAL_CTX
.set i, 0
.rept 31
# Set i = 1. i = 0 is the zero register and is a waste of time.
.set i, 1
.rept 30
save_gp %i
.set i, i+1
.endr
@ -63,17 +60,16 @@ m_trap_vector:
csrr t6, mscratch
save_gp 31, t5
# csrr t0, satp
# sd t0, 32*8(t5)
# We need to check the status of the floating
# point system. (FS bits are described in 3.1.6.5
# and table 3.3 in the RISC-V Privilege spec).
csrr t1, mstatus
srli t0, t1, 13
andi t0, t0, 3
li t1, 3
# Skip saving the FP registers if the FP is turned off.
bne t0, t1, 3f
la t6, _GLOBAL_CTX
beqz t0, 3f
la t6, _GLOBAL_CTX
.set i, 0
.rept 32
save_fp %i
@ -85,23 +81,38 @@ m_trap_vector:
# usize trap_handler(mepc, mcause)
# trap_handler returns the new mepc
# via a0
la sp, _stack_end
la sp, _stack_end
li t0, 0x10000
csrr t1, mhartid
mul t0, t0, t1
sub sp, sp, t0
csrr a0, mepc
csrr a1, mtval
csrr a2, mcause
csrr a3, mhartid
call m_trap
csrr a4, mstatus
la t1, m_trap
csrw mepc, t1
la ra, 3f
li t2, 0b11 << 11
csrw mstatus, t2
mret
3:
csrw mepc, a0
# Move to the context for this CPU
la t6, _GLOBAL_CTX
# Go to the context for this hart
csrr t5, mhartid
slli t5, t5, 6
add t6, t6, t5
csrr t1, mstatus
srli t0, t1, 13
andi t0, t0, 3
li t1, 3
# Skip loading the FP registers if the FP is turned off.
bne t0, t1, 3f
beqz t0, 3f
.set i, 0
.rept 32
load_fp %i
@ -109,128 +120,22 @@ m_trap_vector:
.endr
3:
# csrr t5, mhartid
# slli t5, t5, CTX_SHL
# add t6, t6, t5
# Restore the registers
.set i, 0
.rept 32
load_gp %i
.set i, i+1
.endr
# Get the MMU going
csrw mscratch, t6
la t6, _GLOBAL_CTX
ld t6, 32*8(t6)
csrw satp, t6
sfence.vma
csrr t6, mscratch
# x31 gets restored at the last iteration
mret
.global s_trap_vector
# This must be aligned by 4 since the last two bits
# of the mtvec register do not contribute to the address
# of this vector.
.align 4
s_trap_vector:
# We have to save t6 (x31), since it will be our
# base register for saving
csrw sscratch, t6
# Disable the MMU since we're switching.
csrr t6, satp
slli t6, t6, 4
srli t6, t6, 4
csrw satp, t6
# Disable interrupts
li t6, 1 << 3
csrrc zero, sstatus, t6
# Start saving the registers. We can't do much until the registers
# have been saved.
la t6, _GLOBAL_CTX
.set i, 0
.set i, 1
.rept 31
save_gp %i
.set i, i+1
.endr
# We saved 31 registers. All but t6
# t5 is saved, so we can overwrite it.
mv t5, t6
csrr t6, sscratch
save_gp 31, t5
# csrr t0, satp
# sd t0, 32*8(t5)
csrr t1, sstatus
srli t0, t1, 13
andi t0, t0, 3
li t1, 3
# Skip saving the FP registers if the FP is turned off.
bne t0, t1, 3f
la t6, _GLOBAL_CTX
.set i, 0
.rept 32
save_fp %i
.set i, i+1
.endr
3:
# Go to Rust
# usize trap_handler(mepc, mcause)
# trap_handler returns the new mepc
# via a0
la sp, _stack_end
csrr a0, sepc
csrr a1, stval
csrr a2, scause
call s_trap
csrw sepc, a0
# Move to the context for this CPU
la t6, _GLOBAL_CTX
csrr t1, sstatus
srli t0, t1, 13
andi t0, t0, 3
li t1, 3
# Skip loading the FP registers if the FP is turned off.
bne t0, t1, 3f
.set i, 0
.rept 32
load_fp %i
.set i, i+1
.endr
3:
# csrr t5, mhartid
# slli t5, t5, CTX_SHL
# add t6, t6, t5
# Restore the registers
.set i, 0
.rept 32
load_gp %i
.set i, i+1
.endr
# Get the MMU going
csrw sscratch, t6
la t6, _GLOBAL_CTX
ld t6, 32*8(t6)
csrw satp, t6
sfence.vma
csrr t6, mscratch
# The MMU should be going at this point via
# Rust.
li t2, (1 << 8) | (1 << 5)
csrw mstatus, t2
# x31 gets restored at the last iteration
sret
.global make_syscall
make_syscall:
ecall

6
risc_v/ch4/src/kmem.rs
View File

@ -79,10 +79,10 @@ pub fn get_num_allocations() -> usize {
/// alloc/dealloc from the page crate.
pub fn init() {
unsafe {
// Allocate 64 kernel pages (64 * 4096 = 262 KiB)
let k_alloc = zalloc(64);
// Allocate kernel pages (KMEM_ALLOC)
KMEM_ALLOC = 512;
let k_alloc = zalloc(KMEM_ALLOC);
assert!(!k_alloc.is_null());
KMEM_ALLOC = 64;
KMEM_HEAD = k_alloc as *mut AllocList;
(*KMEM_HEAD).set_free();
(*KMEM_HEAD).set_size(KMEM_ALLOC * PAGE_SIZE);

58
risc_v/ch4/src/lib.rs
View File

@ -146,12 +146,12 @@ extern "C" fn kinit() -> usize {
println!("DATA: 0x{:x} -> 0x{:x}", DATA_START, DATA_END);
println!("BSS: 0x{:x} -> 0x{:x}", BSS_START, BSS_END);
println!("STACK: 0x{:x} -> 0x{:x}", KERNEL_STACK_START, KERNEL_STACK_END);
println!("HEAP: 0x{:x} -> 0x{:x}", kheap_head, kheap_head + total_pages * 4096);
println!("HEAP: 0x{:x} -> 0x{:x}", kheap_head, kheap_head + total_pages * page::PAGE_SIZE);
}
id_map_range(
&mut root,
kheap_head,
kheap_head + total_pages * 4096,
kheap_head + total_pages * page::PAGE_SIZE,
page::EntryBits::ReadWrite.val(),
);
unsafe {
@ -203,38 +203,20 @@ extern "C" fn kinit() -> usize {
}
// UART
page::map(
&mut root,
0x1000_0000,
0x1000_0000,
page::EntryBits::ReadWrite.val(),
0
id_map_range(
&mut root,
0x1000_0000,
0x1000_0100,
page::EntryBits::ReadWrite.val(),
);
// CLINT
// -> MSIP
page::map(
&mut root,
0x0200_0000,
0x0200_0000,
page::EntryBits::ReadWrite.val(),
0
);
// -> MTIMECMP
page::map(
&mut root,
0x0200_b000,
0x0200_b000,
page::EntryBits::ReadWrite.val(),
0
);
// -> MTIME
page::map(
&mut root,
0x0200_c000,
0x0200_c000,
page::EntryBits::ReadWrite.val(),
0
id_map_range(
&mut root,
0x0200_0000,
0x0200_ffff,
page::EntryBits::ReadWrite.val(),
);
// PLIC
id_map_range(
@ -255,7 +237,7 @@ extern "C" fn kinit() -> usize {
// space application requires services. Since the user space application
// only knows virtual addresses, we have to translate silently behind
// the scenes.
let p = 0x0200_0000 as usize;
let p = 0x0200_4000 as usize;
let m = page::virt_to_phys(&root, p).unwrap_or(0);
println!("Walk 0x{:x} = 0x{:x}", p, m);
// When we return from here, we'll go back to boot.S and switch into
@ -271,6 +253,7 @@ extern "C" fn kinit() -> usize {
// We have to store the kernel's table. The tables will be moved back
// and forth between the kernel's table and user applicatons' tables.
KERNEL_TABLE = root_u;
println!("Setting 0x{:x}", KERNEL_TABLE);
}
// table / 4096 Sv39 mode
(root_u >> 12) | (8 << 60)
@ -290,18 +273,23 @@ extern "C" fn kmain() {
// We have the global allocator, so let's see if that works!
let k = Box::<u32>::new(100);
println!("Boxed value = {}", *k);
kmem::print_table();
// The following comes from the Rust documentation:
// some bytes, in a vector
let sparkle_heart = vec![240, 159, 146, 150];
// We know these bytes are valid, so we'll use `unwrap()`.
// This will MOVE the vector.
let sparkle_heart = String::from_utf8(sparkle_heart).unwrap();
println!("String = {}", sparkle_heart);
println!("\n\nAllocations of a box, vector, and string");
kmem::print_table();
}
println!("\n\nEverything should now be free:");
kmem::print_table();
unsafe {
let val = 0x0200_0000 as *mut u32;
val.write_volatile(1);
asm!("ecall");
// asm!("csrw sip, $0" :: "r"(1));
let mtimecmp = 0x0200_4000 as *mut u64;
let mtime = 0x0200_bff8 as *const u64;
mtimecmp.write_volatile(mtime.read_volatile() + 10_000_000);
}
// If we get here, the Box, vec, and String should all be freed since
// they go out of scope. This calls their "Drop" trait.

9
risc_v/ch4/src/page.rs
View File

@ -285,12 +285,12 @@ pub fn print_page_allocations() {
}
println!("~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~");
println!(
"Allocated: {:>5} pages ({:>9} bytes).",
"Allocated: {:>6} pages ({:>10} bytes).",
num,
num * PAGE_SIZE
);
println!(
"Free : {:>5} pages ({:>9} bytes).",
"Free : {:>6} pages ({:>10} bytes).",
num_pages - num,
(num_pages - num) * PAGE_SIZE
);
@ -459,7 +459,10 @@ pub fn map(root: &mut Table, vaddr: usize, paddr: usize, bits: i64, level: usize
(ppn[1] << 19) as i64 | // PPN[1] = [27:19]
(ppn[0] << 10) as i64 | // PPN[0] = [18:10]
bits | // Specified bits, such as User, Read, Write, etc
EntryBits::Valid.val(); // Valid bit
EntryBits::Valid.val() | // Valid bit
EntryBits::Dirty.val() | // Some machines require this to =1
EntryBits::Access.val() // Just like dirty, some machines require this
;
// Set the entry. V should be set to the correct pointer by the loop
// above.
v.set_entry(entry);

45
risc_v/ch4/src/trap.rs
View File

@ -9,7 +9,7 @@ extern "C" {
#[no_mangle]
extern "C"
fn s_trap(epc: usize, tval: usize, cause: usize) -> usize {
fn s_trap(epc: usize, tval: usize, cause: isize) -> usize {
println!("STRAP (cause: 0x{:x} @ 0x{:x})", cause, epc);
unsafe {
// Switch to kernel's page table.
@ -17,12 +17,47 @@ fn s_trap(epc: usize, tval: usize, cause: usize) -> usize {
let satp = KERNEL_TABLE >> 12 | 8 << 60;
asm!("csrw satp, $0" :: "r"(satp));
}
epc + 4
if cause < 0 {
epc
}
else {
epc + 4
}
}
#[no_mangle]
extern "C"
fn m_trap(epc: usize, tval: usize, cause: usize, hart: usize) -> usize {
println!("MTRAP (cause: 0x{:x} @ 0x{:x})", cause, epc);
epc + 4
fn m_trap(epc: usize, tval: usize, cause: isize, hart: usize, stat: usize) -> usize {
println!("MTRAP ({}) (cause: 0x{:x} @ 0x{:x}) [0x{:x}]", hart, cause, epc, stat);
unsafe {
if cause < 0 {
// Asynchronous
match cause & 0xff {
4 | 5 | 7 => {
let satp: usize = KERNEL_TABLE >> 12 | 8 << 60;
println!("Kernel table = 0x{:x}", KERNEL_TABLE);
// asm!("csrw satp, $0" :: "r"(satp) :: "volatile");
// asm!("sfence.vma" :::: "volatile");
// asm!("csrw mie, zero" :::: "volatile");
},
_ => { println!("Async cause\n"); }
}
}
else {
match cause {
2 => {
panic!("Illegal instruction");
},
12 => {
panic!("Instruction page fault.");
},
13 => {
panic!("Load page fault.");
},
_ => { println!("Sync cause\n"); }
}
}
}
epc
}