amd64 processor low level functions

[zos] / spinlock.s

diff --git a/spinlock.s b/spinlock.s
new file mode 100644 (file)
index 0000000..37849b2
--- /dev/null
+++ b/spinlock.s
@@ -0,0 +1,30 @@
+global spinlock_acquire:function
+global spinlock_release:function
+global spinlock_init:function
+
+; spinlock addr in rdi
+; low four bytes is ticket number
+; high four bytes is turn counter
+
+spinlock_init:
+       mov rax, 0
+       mov [rdi], rax
+       ret
+
+spinlock_acquire:
+       mov eax, 1
+       lock xadd [rdi], eax   ; eax = my ticket number
+
+       cmp [rdi+4], eax        ; is it my turn?
+       je .acquired             ; yes
+
+.retry:
+       pause
+       cmp [rdi+4], eax        ; is it my turn?
+       jne .retry                ; keep waiting
+.acquired:
+       ret
+
+spinlock_release:
+       lock inc dword [rdi+4]
+       ret