4 files changed, 174 insertions, 0 deletions
diff --git a/src/base/coro/coro.c b/src/base/coro/coro.c
new file mode 100644
index 0000000..2255c99
--- /dev/null
+++ b/src/base/coro/coro.c
@@ -0,0 +1,43 @@
+#include "internal.h"
+
+/* Co-routine context */
+Coro*
+coro·make(uintptr stk, uintptr (*func)(Coro*, uintptr))
+{
+    if (!func) return nil;
+    if (stk == 0) stk = 8192;
+
+    byte *block = malloc(stk);
+    Coro *co    = (Coro*)&block[stk - sizeof(Coro)];
+    co->bp      = block;
+    co->size    = stk;
+
+    _newcoro(co, func, co);
+    return co;
+}
+
+error
+coro·free(Coro *co)
+{
+    enum 
+    {
+        NIL,
+        GOOD,
+        EMPTY,
+        LOST,
+    };
+
+    if (!co)           return NIL;
+    if (!co->bp)       return LOST;
+    if (co->size == 0) return EMPTY;
+
+    free(co->bp);
+
+    return GOOD;
+}
+
+uintptr
+coro·yield(Coro *c, uintptr arg)
+{
+    return _coroyield(c, arg);
+}
diff --git a/src/base/coro/internal.h b/src/base/coro/internal.h
new file mode 100644
index 0000000..f57d27b
--- /dev/null
+++ b/src/base/coro/internal.h
@@ -0,0 +1,15 @@
+#pragma once
+
+#include <u.h>
+#include <base.h>
+
+extern void    _newcoro(Coro *co, uintptr (*func)(Coro*, uintptr), void *stk);
+extern uintptr _coroyield(Coro *co, uintptr arg);
+
+struct Coro
+{
+    void   *sp;
+    void   *bp;
+    uintptr size;
+    void   *user;
+};
diff --git a/src/base/coro/rules.mk b/src/base/coro/rules.mk
new file mode 100644
index 0000000..c2ee89f
--- /dev/null
+++ b/src/base/coro/rules.mk
@@ -0,0 +1,3 @@
+SRCS_$(d)+=\
+	$(d)/coro/coro.c\
+	$(d)/coro/unix_x64.s\
diff --git a/src/base/coro/unix_x64.s b/src/base/coro/unix_x64.s
new file mode 100644
index 0000000..d7de2a2
--- /dev/null
+++ b/src/base/coro/unix_x64.s
@@ -0,0 +1,113 @@
+; Nicholas Noll 2019
+;
+; ===================================================================
+%use altreg
+
+    bits 64
+    default rel
+    global _newcoro
+    global _coroyield
+
+; ===================================================================
+    section .text
+; -------------------------------------------------------------------
+
+%assign L.coro  -8
+%assign L.func  -16
+
+coroinit:
+    mov     R7, [RBP + L.coro]
+    mov     R6, R0 
+    call    [RBP + L.func]
+
+rerun:
+    mov     R7, [RBP + L.coro]
+    mov     R6, R0
+    call    _coroyield
+    jmp     rerun
+
+; -------------------------------------------------------------------
+; # Register Mapping
+; 
+; R0   R1   R2   R3   R4   R5   R6   R7   R8  ...
+; RAX  RCX  RDX  RBX  RSP  RBP  RSI  RDI  R8  ...
+; 
+; # Sys V calling convention
+; func(R7, R6, R2, R1, R8, R9, Z0-7): R0
+;
+; # Stack layout of an in-flight coro
+; *coro
+; *func
+; *bp (base pointer of stack)
+; ....... STACK .........
+; Saved Clobbers
+;
+; ###
+; Stack layout of an init coro
+; Stores the func pointer to init 
+; Stores the clobber registers.
+;
+; L.coro        [8] 
+; L.func        [7]
+; coroinit      [6]
+; RBP           [5]
+; R3            [4]
+; R12           [3]
+; R13           [2]
+; R14           [1]
+; R15           [0]
+
+%define WORDSZ 8
+%define NSAVES 9 
+
+; coro *coro·new(co *coro, fn func, bp *stack)
+_newcoro:
+    lea     R0, [coroinit]              ; Store address of init function
+    lea     R1, [R2 - NSAVES*WORDSZ]    ; Store offset address of stack
+    
+    mov     [R1 + 8*WORDSZ], R7         ; Store context pointer
+    mov     [R1 + 7*WORDSZ], R6         ; Store function pointer
+    mov     [R1 + 6*WORDSZ], R0         ; Store initializer pointer
+    mov     [R1 + 5*WORDSZ], R2         ; Store stack base pointer
+
+    xor     R0, R0
+
+    ; Start of mutable stack
+    ; Blank out the clobbers
+    mov     [R1 + 4*WORDSZ], R0 ; R3
+    mov     [R1 + 3*WORDSZ], R0 ; R12
+    mov     [R1 + 2*WORDSZ], R0 ; R13
+    mov     [R1 + 1*WORDSZ], R0 ; R14
+    mov     [R1 + 0*WORDSZ], R0 ; R15
+
+    mov     [R7], R1
+    ret
+
+; Saves register state
+%macro pushclobs 0
+    push     RBP
+    push     R3
+    push     R12
+    push     R13
+    push     R14
+    push     R15
+%endmacro
+
+; Restores register state
+%macro popclobs 0
+    pop      R15
+    pop      R14
+    pop      R13
+    pop      R12
+    pop      R3
+    pop      RBP
+%endmacro
+
+; uintptr coro.yield(co *coro, data uintptr)
+_coroyield:
+    pushclobs
+    mov     R0, R6      ; Move return value into return register.
+    xchg    RSP, [R7]   ; Atomically swap the stack pointer with the yieldee. 
+    popclobs
+
+    ret