1 files changed, 42 insertions, 0 deletions
diff --git a/lib/arch/arm64/yield.s b/lib/arch/arm64/yield.s
new file mode 100644
index 0000000..63a4051
--- /dev/null
+++ b/lib/arch/arm64/yield.s
@@ -0,0 +1,42 @@
+# Copyright (c) 2020 Johannes Stoelp
+
+    .arch armv8-a
+    .section .text, "ax", @progbits
+
+    # extern "C" void yield(const void* new_stack, void* const* old_stack);
+    #                                   ^^^^^^^^^               ^^^^^^^^^
+    #                                   rdi                     rsi
+    .global yield
+    .type   yield, @function
+yield:
+    .cfi_startproc
+    // prologue
+    stp x29, x30, [sp, -16]!
+    mov x29, sp
+
+    // push callee saved registers
+    stp x27, x28, [sp, -16]!
+    stp x25, x26, [sp, -16]!
+    stp x23, x24, [sp, -16]!
+    stp x21, x22, [sp, -16]!
+    stp x19, x20, [sp, -16]!
+
+    // arg0: x0 holds new stack
+    // arg1: x1 holds addr to location current stack must be saved
+    mov x2, sp
+    str x2, [x1]  // save current stack ptr
+    mov sp, x0    // switch to new stack ptr
+
+    // pop callee saved registers
+    ldp x19, x20, [sp], 16
+    ldp x21, x22, [sp], 16
+    ldp x23, x24, [sp], 16
+    ldp x25, x26, [sp], 16
+    ldp x27, x28, [sp], 16
+
+    // epilogue
+    ldp x29, x30, [sp], 16
+
+    ret
+    .cfi_endproc
+    .size yield, .-yield