mos/x86_64: cpu: Add atomic swap primitive + MU if

The atomic swap primitive can be used to implement spinlocks among other
things. This must be implemented per architecture as it is exposed via
the machine unifier.

Signed-off-by: Ian Moffett <ian@osmora.org>

2 files changed, 16 insertions, 0 deletions

diff --git a/mos/sys/arch/x86_64/cpu/prim.S b/mos/sys/arch/x86_64/cpu/prim.S
index 6f82153..707eb86 100644
--- a/mos/sys/arch/x86_64/cpu/prim.S
+++ b/mos/sys/arch/x86_64/cpu/prim.S
@@ -7,6 +7,7 @@
     .globl mu_cpu_halt
     .globl mu_irq_state
     .globl mu_irq_setmask
+    .globl mu_cpu_aswap
 mu_cpu_halt:
     hlt
     retq
@@ -19,6 +20,10 @@ mu_irq_state:
     shr $9, %rax        /* IF */
     and $1, %rax        /* Isolate */
     retq
+mu_cpu_aswap:
+    xchg %rsi, (%rdi)   /* Swap */
+    mov %rsi, %rax      /* Return old value */
+    retq
 mu_irq_setmask:
     test $1, %rdi
     jnz irq_mask
diff --git a/mos/sys/inc/mu/cpu.h b/mos/sys/inc/mu/cpu.h
index e91a084..9856df8 100644
--- a/mos/sys/inc/mu/cpu.h
+++ b/mos/sys/inc/mu/cpu.h
@@ -23,6 +23,17 @@ BOOL mu_irq_state(void);
 void mu_irq_setmask(BOOL mask);
 
 /*
+ * Perform an atomic swap operation
+ *
+ * @p: Memory area to store `val' to
+ * @val: Value to write to `p'
+ *
+ * Returns the value at `p' before `val' was
+ * written
+ */
+USIZE mu_cpu_aswap(USIZE *p, USIZE val);
+
+/*
  * Halt the current processor core
  */
 void mu_cpu_halt(void);