Add fiber implementation for LoongArch64

.github/workflows/main.yml

@@ -648,6 +648,11 @@ jobs:
         - target: riscv32imac-unknown-none-elf
           os: ubuntu-latest
           test: cargo check -p wasmtime --no-default-features --features runtime,gc,component-model,async
+        # Use `cross` for loongarch64 to have a C compiler/linker available.
+        - target: loongarch64-unknown-linux-gnu
+          os: ubuntu-latest
+          cross: true
+          test: cross build --target loongarch64-unknown-linux-gnu
     env: ${{ matrix.env || fromJSON('{}') }}
     steps:
     - uses: actions/checkout@v6
@@ -656,9 +661,7 @@ jobs:
     - uses: ./.github/actions/install-rust
     - run: rustup target add ${{ matrix.target }}
     - name: Install cross
-      run: |
-        curl -L --proto '=https' --tlsv1.2 -sSf https://raw.githubusercontent.com/cargo-bins/cargo-binstall/main/install-from-binstall-release.sh | bash
-        cargo binstall --no-confirm cross
+      run: cargo install cross --git https://github.com/cross-rs/cross
       if: ${{ matrix.cross }}
     - uses: ./.github/actions/apt-get-install
       if: ${{ matrix.apt_packages }}

crates/fiber/src/stackswitch.rs

@@ -33,6 +33,10 @@ cfg_if::cfg_if! {
         mod riscv32imac;
         pub(crate) use supported::*;
         pub(crate) use riscv32imac::*;
+    } else if #[cfg(target_arch = "loongarch64")]  {
+        mod loongarch64;
+        pub(crate) use supported::*;
+        pub(crate) use loongarch64::*;
     } else {
         // No support for this platform. Don't fail compilation though and
         // instead defer the error to happen at runtime when a fiber is created.

crates/fiber/src/stackswitch/loongarch64.rs

@@ -0,0 +1,168 @@
+// A WORD OF CAUTION
+//
+// This entire file basically needs to be kept in sync with itself. It's not
+// really possible to modify just one bit of this file without understanding
+// all the other bits. Documentation tries to reference various bits here and
+// there but try to make sure to read over everything before tweaking things!
+
+use core::arch::naked_asm;
+
+#[inline(never)] // FIXME(rust-lang/rust#148307)
+pub(crate) unsafe extern "C" fn wasmtime_fiber_switch(top_of_stack: *mut u8) {
+    unsafe { wasmtime_fiber_switch_(top_of_stack) }
+}
+
+#[unsafe(naked)]
+unsafe extern "C" fn wasmtime_fiber_switch_(top_of_stack: *mut u8 /* a0 */) {
+    naked_asm!(
+        "
+      // Save all callee-saved registers on the stack since we're
+      // assuming they're clobbered as a result of the stack switch.
+      st.d $ra, $sp, -0x08
+      st.d $fp, $sp, -0x10
+      st.d $s0, $sp, -0x18
+      st.d $s1, $sp, -0x20
+      st.d $s2, $sp, -0x28
+      st.d $s3, $sp, -0x30
+      st.d $s4, $sp, -0x38
+      st.d $s5, $sp, -0x40
+      st.d $s6, $sp, -0x48
+      st.d $s7, $sp, -0x50
+      st.d $s8, $sp, -0x58
+      fst.d $fs0, $sp, -0x60
+      fst.d $fs1, $sp, -0x68
+      fst.d $fs2, $sp, -0x70
+      fst.d $fs3, $sp, -0x78
+      fst.d $fs4, $sp, -0x80
+      fst.d $fs5, $sp, -0x88
+      fst.d $fs6, $sp, -0x90
+      fst.d $fs7, $sp, -0x98
+      addi.d $sp, $sp, -0xa0
+
+      // Load our previously saved stack pointer to resume to, and save
+      // off our current stack pointer on where to come back to
+      // eventually.
+      ld.d $t0, $a0, -0x10
+      st.d $sp, $a0, -0x10
+
+      // Switch to the new stack and restore all our callee-saved
+      // registers after the switch and return to our new stack.
+      move $sp, $t0
+
+      fld.d $fs7, $sp, 0x08
+      fld.d $fs6, $sp, 0x10
+      fld.d $fs5, $sp, 0x18
+      fld.d $fs4, $sp, 0x20
+      fld.d $fs3, $sp, 0x28
+      fld.d $fs2, $sp, 0x30
+      fld.d $fs1, $sp, 0x38
+      fld.d $fs0, $sp, 0x40
+      ld.d $s8, $sp, 0x48
+      ld.d $s7, $sp, 0x50
+      ld.d $s6, $sp, 0x58
+      ld.d $s5, $sp, 0x60
+      ld.d $s4, $sp, 0x68
+      ld.d $s3, $sp, 0x70
+      ld.d $s2, $sp, 0x78
+      ld.d $s1, $sp, 0x80
+      ld.d $s0, $sp, 0x88
+      ld.d $fp, $sp, 0x90
+      ld.d $ra, $sp, 0x98
+      addi.d $sp, $sp, 0xa0
+      ret
+        ",
+    );
+}
+
+pub(crate) unsafe fn wasmtime_fiber_init(
+    top_of_stack: *mut u8,
+    entry_point: extern "C" fn(*mut u8, *mut u8) -> *mut u8,
+    entry_arg0: *mut u8,
+) {
+    #[repr(C)]
+    #[derive(Default)]
+    struct InitialStack {
+        align_to_16_byte_size: u64,
+
+        fs: [f64; 8],
+
+        s8: *mut u8,
+        s7: *mut u8,
+        s6: *mut u8,
+        s5: *mut u8,
+        s4: *mut u8,
+        s3: *mut u8,
+        s2: *mut u8,
+        s1: *mut u8,
+        s0: *mut u8,
+
+        fp: *mut u8,
+        ra: *mut u8,
+
+        // unix.rs reserved space
+        last_sp: *mut u8,
+        run_result: *mut u8,
+    }
+
+    unsafe {
+        let initial_stack = top_of_stack.cast::<InitialStack>().sub(1);
+        initial_stack.write(InitialStack {
+            s0: entry_point as *mut u8,
+            s1: entry_arg0,
+            s2: wasmtime_fiber_switch_ as *mut u8,
+            fp: top_of_stack,
+            ra: wasmtime_fiber_start as *mut u8,
+            last_sp: initial_stack.cast(),
+            ..InitialStack::default()
+        });
+    }
+}
+
+#[unsafe(naked)]
+unsafe extern "C" fn wasmtime_fiber_start() -> ! {
+    naked_asm!(
+        "
+    .cfi_startproc simple
+    .cfi_def_cfa_offset 0
+
+
+    .cfi_escape 0x0f, /* DW_CFA_def_cfa_expression */ \
+        5,             /* the byte length of this expression */ \
+        0x53,          /* DW_OP_reg3 (sp) */ \
+        0x06,          /* DW_OP_deref */ \
+        0x08, 0xa0,    /* DW_OP_const1u 0x98 */ \
+        0x22           /* DW_OP_plus */
+
+
+      .cfi_rel_offset ra, -0x8
+      .cfi_rel_offset fp, -0x10
+      .cfi_rel_offset s0, -0x18
+      .cfi_rel_offset s1, -0x20
+      .cfi_rel_offset s2, -0x28
+      .cfi_rel_offset s3, -0x30
+      .cfi_rel_offset s4, -0x38
+      .cfi_rel_offset s5, -0x40
+      .cfi_rel_offset s6, -0x48
+      .cfi_rel_offset s7, -0x50
+      .cfi_rel_offset s8, -0x58
+      .cfi_rel_offset fs0, -0x60
+      .cfi_rel_offset fs1, -0x68
+      .cfi_rel_offset fs2, -0x70
+      .cfi_rel_offset fs3, -0x78
+      .cfi_rel_offset fs4, -0x80
+      .cfi_rel_offset fs5, -0x88
+      .cfi_rel_offset fs6, -0x90
+      .cfi_rel_offset fs7, -0x98
+
+      move $a0, $s1
+      move $a1, $fp
+      jirl $ra, $s0, 0 // entry_point
+      jirl $ra, $s2, 0 // wasmtime_fiber_switch_
+
+      // .4byte 0 will cause panic.
+      // for safety just like x86_64.rs.
+      .4byte 0
+      .cfi_endproc
+  ",
+    );
+}