setup new stack + basic yielding between two stacks

1 files changed, 65 insertions, 0 deletions

diff --git a/lib/thread_create.s b/lib/thread_create.s
new file mode 100644
index 0000000..6d6fa96
--- /dev/null
+++ b/lib/thread_create.s
@@ -0,0 +1,65 @@
+# SysV AMD64 ABI
+# int/ptr args : rdi, rsi, rdx, rcx, r8, r9
+# int/ptr ret  : rax
+
+    .intel_syntax noprefix
+    .section .text ,"ax",@progbits
+
+     # extern "C" void thread_create();
+    .global thread_create
+    .type   thread_create, @function
+thread_create:
+    .cfi_startproc
+    mov rdi, qword ptr [rsp+0x8]
+    mov rsi, qword ptr [rsp]
+
+    call rsi
+
+    # FIXME: no return from thread after user fn finished.
+1:
+    jmp 1b
+    .cfi_endproc
+    .size thread_create, .-thread_create
+
+
+
+    # extern "C" void yield(void* new_stack, void** old_stack);
+    #                             ^^^^^^^^^         ^^^^^^^^^
+    #                             rdi               rsi
+    .global yield
+    .type   yield, @function
+yield:
+    .cfi_startproc
+    // prologue
+    push rbp
+    mov rbp, rsp
+
+    // push callee saved registers
+    push rbx
+    push rbp
+    push r12
+    push r13
+    push r14
+    push r15
+
+    // arg0: rdi holds new stack
+    // arg1: rsi holds addr to location current stack must be saved
+    mov [rsi], rsp  # save current stack ptr
+    mov rsp, rdi    # switch to new stack ptr
+
+    // pop callee saved registers
+    pop r15
+    pop r14
+    pop r13
+    pop r12
+    pop rbp
+    pop rbx
+
+    // epilogue
+    mov rsp, rbp
+    pop rbp
+
+    ret
+    .cfi_endproc
+    .size yield, .-yield
+