Implement system calls on RISC-V in libtock_runtime.
This introduces `TockSyscalls`, which implements `libtock_platform::Syscalls` indirectly by directly implementing `libtock_platform::RawSyscalls`. I will implement ARM system calls in a future PR.
diff --git a/core/runtime/src/lib.rs b/core/runtime/src/lib.rs
index d7ea623..b0daf03 100644
--- a/core/runtime/src/lib.rs
+++ b/core/runtime/src/lib.rs
@@ -18,4 +18,11 @@
//! `no_auto_layout` feature on `libtock_runtime` to disable this functionality
//! and provide its own layout file.
+#![feature(asm)]
#![no_std]
+
+/// TockSyscalls implements `libtock_platform::Syscalls`.
+pub struct TockSyscalls;
+
+#[cfg(target_arch = "riscv32")]
+mod syscalls_impl_riscv;
diff --git a/core/runtime/src/syscalls_impl_riscv.rs b/core/runtime/src/syscalls_impl_riscv.rs
new file mode 100644
index 0000000..d58ce5e
--- /dev/null
+++ b/core/runtime/src/syscalls_impl_riscv.rs
@@ -0,0 +1,82 @@
+use libtock_platform::{OneArgMemop, RawSyscalls, YieldType, ZeroArgMemop};
+
+impl RawSyscalls for crate::TockSyscalls {
+ // This yield implementation is currently limited RISC-V versions without
+ // floating-point registers, as it does not mark them clobbered.
+ #[cfg(not(any(target_feature = "d", target_feature = "f")))]
+ fn raw_yield(r0_in: YieldType) -> u32 {
+ let mut r0 = r0_in as u32;
+ let mut _a4 = 0;
+ unsafe {
+ asm!("ecall",
+ // x0 is a constant.
+ lateout("x1") _, // Return address
+ // x2-x4 are stack, global, and thread pointers. sp is
+ // callee-saved.
+ lateout("x5") _,
+ lateout("x6") _,
+ lateout("x7") _,
+ // x8 and x9 are callee-saved.
+ inlateout("x10") r0,
+ lateout("x11") _,
+ lateout("x12") _,
+ lateout("x13") _,
+ inlateout("x14") _a4,
+ lateout("x15") _,
+ lateout("x16") _,
+ lateout("x17") _,
+ // x18-27 (aka s2-s11) are callee-saved
+ lateout("x28") _,
+ lateout("x29") _,
+ lateout("x30") _,
+ lateout("x31") _,
+ );
+ }
+ r0
+ }
+
+ unsafe fn four_arg_syscall(
+ mut r0: u32,
+ mut r1: u32,
+ mut r2: usize,
+ mut r3: usize,
+ class: u8,
+ ) -> (u32, usize, usize, usize) {
+ asm!("ecall",
+ inlateout("a0") r0,
+ inlateout("a1") r1,
+ inlateout("a2") r2,
+ inlateout("a3") r3,
+ in("a4") class,
+ options(preserves_flags, nostack),
+ );
+ (r0, r1 as usize, r2, r3)
+ }
+
+ fn zero_arg_memop(r0_in: ZeroArgMemop) -> (u32, usize) {
+ let mut r0 = r0_in as u32;
+ let r1;
+ unsafe {
+ asm!("ecall",
+ inlateout("a0") r0,
+ lateout("a1") r1,
+ in("a4") 5,
+ options(preserves_flags, nostack, nomem),
+ );
+ }
+ (r0, r1)
+ }
+
+ fn one_arg_memop(r0_in: OneArgMemop, mut r1: usize) -> (u32, usize) {
+ let mut r0 = r0_in as u32;
+ unsafe {
+ asm!("ecall",
+ inlateout("a0") r0,
+ inlateout("a1") r1,
+ in("a4") 5,
+ options(preserves_flags, nostack, nomem)
+ );
+ }
+ (r0, r1)
+ }
+}
