From 4442d27b620570c1f788d867ccbdc79d686f34ce Mon Sep 17 00:00:00 2001
From: Yann MAGNIN <yann.magnin@protonmail.com>
Date: Tue, 1 Apr 2025 15:03:23 +0200
Subject: [PATCH] world: new gint_world_enter() and gint_world_leave()
 primitives

---
 include/gint/gint.h |  9 ++++++++
 src/kernel/exch.c   |  2 ++
 src/kernel/world.c  | 53 +++++++++++++++++++++++++++++++++++++++++++--
 3 files changed, 62 insertions(+), 2 deletions(-)

diff --git a/include/gint/gint.h b/include/gint/gint.h
index 2c4ed09..3cbddb8 100644
--- a/include/gint/gint.h
+++ b/include/gint/gint.h
@@ -41,6 +41,15 @@ int gint_world_switch(gint_call_t function);
 __attribute__((deprecated("Use gint_world_switch() instead")))
 void gint_switch(void (*function)(void));
 
+#define GINT_WORLD_ADDIN    1
+#define GINT_WORLD_OS       0
+
+/* gint_world_enter(): Enter in a new world */
+void gint_world_enter(int world);
+
+/* gint_world_leave(): Leave a world set by gint_world_enter() */
+void gint_world_leave(void);
+
 /* gint_world_sync(): Synchronize asynchronous drivers
 
    This function waits for asynchronous tasks to complete by unbinding all
diff --git a/src/kernel/exch.c b/src/kernel/exch.c
index 5f79567..86458aa 100644
--- a/src/kernel/exch.c
+++ b/src/kernel/exch.c
@@ -81,6 +81,7 @@ GNORETURN static void gint_default_panic(GUNUSED uint32_t code)
 	if(code == 0x1080) name = "Stack overflow";
 	if(code == 0x10a0) name = "UBC in bank 1 code";
 	// if(code == 0x10c0) name = "Missing syscall"; // not on FX
+	if(code == 0x1100) name = "World-switch error";
 
 	if(name[0]) dtext(1, 9, name);
 	else dprint(1, 9, "%03x", code);
@@ -124,6 +125,7 @@ GNORETURN static void gint_default_panic(GUNUSED uint32_t code)
 	if(code == 0x10a0) name = "UBC break in register bank 1 code";
 	if(code == 0x10c0) name = "Missing syscall for this OS version";
 	if(code == 0x10e0) name = "I2C (touch-screen) error";
+	if(code == 0x1100) name = "World-switch error";
 
 	dprint(6, 25, "%03x %s", code, name);
 
diff --git a/src/kernel/world.c b/src/kernel/world.c
index 6a39d27..a984768 100644
--- a/src/kernel/world.c
+++ b/src/kernel/world.c
@@ -3,6 +3,7 @@
 #include <gint/gint.h>
 #include <gint/exc.h>
 #include <gint/defs/call.h>
+#include <gint/defs/util.h>
 #include <gint/hardware.h>
 #include <gint/display.h>
 #include "kernel.h"
@@ -146,10 +147,58 @@ void gint_world_switch_out(gint_world_t world_addin, gint_world_t world_os)
 	cpu_atomic_end();
 }
 
+#ifndef WORLD_SWITCH_STACK_SIZE
+# define WORLD_SWITCH_STACK_SIZE 8
+#endif
+
+static struct {
+    u8 stack[WORLD_SWITCH_STACK_SIZE];
+    int idx;
+} world_switch_stack = {
+    .stack = { GINT_WORLD_ADDIN },
+    .idx = 0,
+};
+
+// FIXME: support CPU atomic operation
+void gint_world_enter(int world)
+{
+    GAUTOTYPE wss = &world_switch_stack;
+
+    if (world != GINT_WORLD_OS && world != GINT_WORLD_ADDIN)
+        gint_panic(0x1100);
+    if (wss->idx >= WORLD_SWITCH_STACK_SIZE)
+        gint_panic(0x1100);
+    if (world != wss->stack[wss->idx])
+    {
+        if (world == GINT_WORLD_OS)
+            gint_world_switch_out(gint_world_addin, gint_world_os);
+        if (world == GINT_WORLD_ADDIN)
+            gint_world_switch_in(gint_world_os, gint_world_addin);
+    }
+    wss->stack[++(wss->idx)] = world;
+}
+
+// FIXME: support CPU atomic operation
+void gint_world_leave(void)
+{
+    GAUTOTYPE wss = &world_switch_stack;
+
+    if (wss->idx == 0)
+        gint_panic(0x1100);
+    if (wss->stack[wss->idx - 0] != wss->stack[wss->idx - 1])
+    {
+        if (wss->stack[wss->idx] == GINT_WORLD_OS)
+            gint_world_switch_in(gint_world_os, gint_world_addin);
+        if (wss->stack[wss->idx] == GINT_WORLD_ADDIN)
+            gint_world_switch_out(gint_world_addin, gint_world_os);
+    }
+    wss->idx -= 1;
+}
+
 int gint_world_switch(gint_call_t call)
 {
 	extern void *gint_stack_top;
-	gint_world_switch_out(gint_world_addin, gint_world_os);
+    gint_world_enter(GINT_WORLD_OS);
 
 	void *ILRAM = (void *)0xe5200000;
 	void *XRAM  = (void *)0xe500e000;
@@ -194,7 +243,7 @@ int gint_world_switch(gint_call_t call)
 	if(canary && *canary != 0xb7c0ffee)
 		gint_panic(0x1080);
 
-	gint_world_switch_in(gint_world_os, gint_world_addin);
+	gint_world_leave();
 	return rc;
 }