Add basic `V_COMMON` exception handler #22

zachary-cauchi · 2024-10-26T19:08:45Z

Adds a basic exception handler to all V_COMMON exceptions.
Add basic panic handler which prints all COP0 register values and halts.
Modify linkfile to specify memory locations for sections.
Fix error messages in VSCode.
Add sleep_thread syscall.
Add saving of EE registers in exception handler before passing to Rust-level handler.
Remove deprecated r0 crate.

Partially addresses #20.

Ravenslofty · 2024-10-27T06:46:46Z

I am unfortunately away from keyboard for like another week, so I probably won't be able to review this until then. If feasible, could you ping me in a week?

Ravenslofty

I suspect the ghost of provenance will haunt us for some time...

Ravenslofty · 2024-10-27T11:39:30Z

prussia_rt/src/cop0.rs

+/// Represents a coredump of the CoP0 registers.
+#[derive(Debug)]
+pub struct CoP0Dump {
+    /// [BadVAddr] value loaded from the BadVAddr register.


something of a philosophy question: how much do we assume someone has read the user manuals? these comments make sense if someone keeps them open, but otherwise they're very self-referential.

I think something like "virtual address of exception" here would be a helpful memory aid, as an example.

Ravenslofty · 2024-10-27T11:42:08Z

prussia_rt/src/cop0.rs

+impl CoP0Dump {
+    /// Dumps all register contents and constructs an instance of [CoP0Dump].
+    pub fn load() -> Self {
+        let bad_v_addr = BadVAddr::load();


I think just directly loading things in the return structure is more succinct; we don't gain any readability by using an intermediate variable.

Ravenslofty · 2024-10-27T12:23:35Z

prussia_rt/src/cop0.rs

@@ -98,8 +184,15 @@ impl EPC {
    pub fn store(self) {
        unsafe { _write_epc(self.0) }
    }
+
+    /// Convert to a raw pointer. Remember to check the `Cause.BD` register field to determine if an offset is needed.
+    pub fn as_raw_ptr(&self) -> *const u32 {


The more I look at this API, the more I'm convinced this is not sound as-is with respect to provenance.

The question is: can it ever be made sound? Playing by the "definitely safe" Strict Provenance rules, we need a pointer that has access to whatever this points to. There's absolutely no way for us to do that here. That means we would have to use Exposed Provenance, and need everything to expose its provenance for it to be sound for us to read through.

So I'm tempted to say that not only should this method be deleted, but the docs updated to tell people not to convert this into a pointer.

Ravenslofty · 2024-10-27T12:52:25Z

prussia_rt/src/exceptions/v_common.rs

+}
+
+#[no_mangle]
+pub(super) extern "C" fn unimplemented_v_common_handler(tcb_ptr: *mut ThreadControlBlock) {


-> !, perhaps? Rust can detect that the infinite loop is diverging, I think.

Ravenslofty · 2024-10-27T12:56:38Z

prussia_rt/src/exceptions/v_common/overflow.rs

+
+use crate::{cop0::CoP0Dump, thread::ThreadControlBlock};
+
+/// Purposefully trigger an overflow exception. For testing purposes.


(thankfully, these went out of style)

Ravenslofty · 2024-10-27T13:14:11Z

prussia_rt/src/lib.rs

    zero_bss();

+    println_ee!("rt - BSS zero-ed out.");
+
+    initialise_exception_vectors();


I think it might be smarter to initialise the vectors before zeroing bss in case the elf is somehow corrupt and bss points to invalid address space.

Ravenslofty · 2024-10-27T13:14:28Z

prussia_rt/src/panic.rs

+
+use crate::cop0::CoP0Dump;
+
+/// Main entrpoint for the [panic_handler](https://doc.rust-lang.org/nomicon/panic-handler.html).


Ravenslofty · 2024-10-27T13:15:19Z

prussia_rt/src/routines.S

@@ -1,6 +1,7 @@
 # The assembler tries to reorder our instructions around delay slots.
 # Since we want to preserve this order, disable the reordering feature.
 .set noreorder
+.set noat


I don't think I smash $at in my code, do I?

Ravenslofty · 2024-10-27T13:15:52Z

prussia_rt/src/routines.S

@@ -1,6 +1,7 @@
 # The assembler tries to reorder our instructions around delay slots.
 # Since we want to preserve this order, disable the reordering feature.
 .set noreorder
+.set noat

 # Bootstrap routine for PruSSia. LLVM only needs a stack pointer, and the rest we can do in Rust.


Eeek. While you're here can you fix the capitalisation of Prussia? :p

Ravenslofty · 2024-10-27T13:18:46Z

prussia_rt/src/thread.rs

+/// jumping to an exception handler.
+#[repr(C)]
+pub(crate) struct ThreadControlBlock {
+    pub at: u64,


I can't remember, is this from my code? If it was, it's technically incorrect because the GPRs are actually 128-bit wide...

zachary-cauchi added 29 commits April 20, 2024 10:33

feat(hello-rs): Add elf-named bin target

c68ae64

feat(prussia_rt): Add base panic handler

de7f89d

fix(hello-rs): Change .elf target to makefile

2033901

feat(prussia_rt): Add cop0 core dump on panic

5ddf33b

feat(prussia_rt): Add event enums to coredump

080c7e9

feat(linkfile): Restructure linkfile to use MEMORY regions

2f3c220

feat(prussia_rt): Add base working exception handler

1271ccc

feat(prussia_rt): Add common cause parsing

6056cac

feat(prussia_rt): Add V_COMMON jump table and handler

f0991bf

feat(prussia_rt): Move v_common exc handling to own file

8c21d14

fix(prussia_rt): Minor warnings

d5a6219

feat(prussia_rt): Add syscall exc handler and init_handlers fn

40aa4f9

feat: Add renaming of bin file to elf

20647c1

feat(prussia_rt): Remove archived r0 crate

75dd09b

feat(prussia_bios): Add sleep_thread syscall

aa3df1c

fix: rust clippy checking all targets

47e5ddb

feat(prussia_rt): Improve syscall exception handler

0a53afa

feat(prussia_debug): Add println_ee macro

c72e7ea

feat(prussia_rt): Add overflow exception handler

d4779a7

feat(prussia_rt): Add tcb struct for register inspection

2fced56

feat(prussia_rt): Add Address Load exception handler

4062baa

feat(prussia_rt): Add address store exc handler

8899068

feat(prussia_rt): Add bus error exception handlers

6e855a4

feat(prussia_rt): Trigger reserved instruction exception

fc40988

feat(prussia_rt): Add cop unusable exception handler

d3ef5d0

feat(prussia_rt): Add trap exception handler

7797d7b

feat(prussia_rt): Improve unknwon err handler

9200178

feat(prussia_rt): Add TLB Modified exception handler

4ab0dd3

feat(prussia_rt): Add TLB Invalid exception handlers

2bc8f55

zachary-cauchi linked an issue Oct 26, 2024 that may be closed by this pull request

Create a basic exception-handler #20

Open

23 tasks

Ravenslofty requested changes Oct 27, 2024

View reviewed changes

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Add basic `V_COMMON` exception handler #22

Add basic `V_COMMON` exception handler #22

zachary-cauchi commented Oct 26, 2024

Ravenslofty commented Oct 27, 2024

Ravenslofty left a comment

Ravenslofty Oct 27, 2024

Ravenslofty Oct 27, 2024

Ravenslofty Oct 27, 2024

Ravenslofty Oct 27, 2024

Ravenslofty Oct 27, 2024

Ravenslofty Oct 27, 2024

Ravenslofty Oct 27, 2024

Ravenslofty Oct 27, 2024

Ravenslofty Oct 27, 2024

Ravenslofty Oct 27, 2024


		use crate::{cop0::CoP0Dump, thread::ThreadControlBlock};

		/// Purposefully trigger an overflow exception. For testing purposes.


		use crate::cop0::CoP0Dump;

		/// Main entrpoint for the [panic_handler](https://doc.rust-lang.org/nomicon/panic-handler.html).

Add basic V_COMMON exception handler #22

Are you sure you want to change the base?

Add basic V_COMMON exception handler #22

Conversation

zachary-cauchi commented Oct 26, 2024

Ravenslofty commented Oct 27, 2024

Ravenslofty left a comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Add basic `V_COMMON` exception handler #22

Add basic `V_COMMON` exception handler #22