implement switching using the Stackman submodule

.gitmodules

@@ -0,0 +1,3 @@
+[submodule "Include/internal/stackman"]
+	path = Include/internal/stackman
+	url = ssh://git@github.com/kristjanvalur/stackman

Include/internal/slp_platformselect.h

@@ -5,6 +5,16 @@
  * Platform Selection for Stackless
  */
 
+/* First, see if stackman an implementation without external
+ * assembler, use that if possible
+ */
+#define STACKMAN_OPTIONAL
+#include "stackman/src/stackman.h"
+#if defined(STACKMAN_PLATFORM) && !defined(STACKMAN_EXTERNAL_ASM)
+#include "internal/slp_switch_stackman.h"
+
+#else  /* use traditional stackless switching */
+
 #if   defined(MS_WIN32) && !defined(MS_WIN64) && defined(_M_IX86)
 #include "internal/slp_switch_x86_msvc.h" /* MS Visual Studio on X86 */
 #elif defined(MS_WIN64) && defined(_M_X64)
@@ -32,6 +42,7 @@
 #elif defined(SN_TARGET_PS3)
 #include "internal/slp_switch_ps3_SNTools.h" /* Sony PS3 */
 #endif
+#endif
 
 /* default definitions if not defined in above files */
 

Include/internal/slp_switch_stackman.h

@@ -0,0 +1,66 @@
+/*
+ * this is the internal transfer function, using
+ * the stackman platform library.
+ * We create a wrapper callback that employs the existing
+ * stack macros.
+ * At some later point in time, the callback could be
+ * written directly.
+ *
+ */
+
+#define SLP_STACK_REFPLUS 1
+
+#ifdef SLP_EVAL
+#define SLP_STACK_MAGIC 0
+
+
+/* need a special function arount SLP_SAVE_STATE() because
+ * the macro has a built-in return of 0 or -1.  Must catch
+ * that.
+ */
+static int slp_stackman_cb_save(void *sp, intptr_t *pdiff)
+{
+    intptr_t diff;
+    SLP_SAVE_STATE(sp, diff);
+    *pdiff = diff;
+    return 1;
+}
+
+static void *slp_stackman_cb(void *_ctxt, int opcode, void *sp)
+{
+    int *error = (int*)_ctxt;
+    intptr_t stsizediff;
+    if (opcode == STACKMAN_OP_SAVE)
+    {
+        int ret = slp_stackman_cb_save(sp, &stsizediff);
+        if (ret == 1) {
+            /* regular switch */
+            return (void*)((char*)sp + stsizediff);
+        } 
+        if (ret == -1)
+        {
+            *error = -1;
+        }
+        /* error or save only, no change in sp */
+        return sp;
+    }
+    else
+    {
+        if (*error != -1)
+            SLP_RESTORE_STATE();
+        return sp;
+    }
+}
+
+static int
+slp_switch(void)
+{
+    /* this can be on the stack, because if there isn't a switch
+     * then it is intact. (error or save only) */
+    int error = 0;
+    stackman_switch(&slp_stackman_cb, &error);
+    return error;
+}
+
+#include "stackman/src/stackman_impl.h"
+#endif