1 files changed, 32 insertions, 0 deletions
diff --git a/lib/arch/arm/yield.s b/lib/arch/arm/yield.s
new file mode 100644
index 0000000..de9d604
--- /dev/null
+++ b/lib/arch/arm/yield.s
@@ -0,0 +1,32 @@
+# Copyright (c) 2021 Johannes Stoelp
+
+    .arch armv7-a
+    .section .text, "ax", %progbits
+
+    # extern "C" void yield(const void* new_stack, void** old_stack);
+    #                                   ^^^^^^^^^         ^^^^^^^^^
+    #                                   x0                x1
+    .global yield
+    .type   yield, %function
+yield:
+    .cfi_startproc
+    // prologue
+    push {fp, lr}
+    mov fp, sp
+
+    // push callee saved registers
+    push {r4-r11}
+
+    // arg0: r0 holds new stack
+    // arg1: r1 holds addr to location current stack must be saved
+    mov r2, sp
+    str r2, [r1]  // save current stack ptr
+    mov sp, r0    // switch to new stack ptr
+
+    // pop callee saved registers
+    pop {r4-r11}
+
+    // epilogue
+    pop {fp, pc}
+    .cfi_endproc
+    .size yield, .-yield