add gecko-{gosub,return}; only load once from memory card

ReadFile-C2.s

@@ -0,0 +1,80 @@
+	.file	"ReadFile.c"
+	.machine ppc
+	.section	".text"
+	.globl onReadOptionBlock
+	.type	onReadOptionBlock, @function
+onReadOptionBlock:
+.LFB0:
+	stwu 1,-32(1)
+	#mflr 0
+	stmw 27,12(1)
+	lis 29,0x817f
+	ori 29,29,0xe800
+	lis 28,0xabcd
+	lwz 9,0(29)
+	ori 28,28,0x1234
+	#stw 0,36(1)
+	mr 30,3
+	cmpw 0,9,28
+	mr 31,4
+	beq- 0,.L3
+	lis 9,mount_@ha
+	li 4,1
+	la 9,mount_@l(9)
+	mtctr 9
+	bctrl
+	cmpwi 0,3,0
+	bne- 0,.L3
+	lis 9,CARDOpen@ha
+	la 9,CARDOpen@l(9)
+	lwz 3,0(30)
+	mr 5,31
+	bl .LC0
+	.string	"gct"
+	.section	".text"
+	.align 2
+.LC0: mflr 4
+	mtctr 9
+	bctrl
+	cmpwi 0,3,0
+	bne- 0,.L3
+	lis 27,0x817f
+	lis 9,CARDRead@ha
+	la 9,CARDRead@l(9)
+	ori 27,27,0xa800
+	li 6,0
+	li 5,16384
+	mr 4,27
+	mr 3,31
+	mtctr 9
+	bctrl
+	cmpwi 0,3,0
+	bne- 0,.L5
+	lwz 9,0(27)
+	xoris 10,9,0xff2f
+	cmpwi 0,10,-16162
+	bne 0,.L5
+	lis 10,0x817f
+	ori 10,10,0xa804
+	lwz 10,0(10)
+	cmpw 0,10,9
+	bne+ 0,.L5
+	stw 28,0(29)
+.L5:
+	lis 9,CARDClose@ha
+	mr 3,31
+	la 9,CARDClose@l(9)
+	mtctr 9
+	bctrl
+.L3:
+	lis 9,open_@ha
+	mr 4,31
+	la 9,open_@l(9)
+	mr 3,30
+	mtctr 9
+	bctrl
+	lmw 27,12(1)
+	addi 1,1,32
+.LFE0:
+	.size	onReadOptionBlock, .-onReadOptionBlock
+	.ident	"GCC: (devkitPPC release 41) 12.1.0"

ReadFile.c

@@ -1,3 +1,5 @@
+#include <stdint.h>
+
 typedef struct {
   char pad[20];
 } CARDFileInfo;
@@ -24,10 +26,16 @@ int CARDRead(CARDFileInfo *fileInfo, void *buf, unsigned long size, unsigned lon
 int CARDClose(CARDFileInfo *fileInfo);
 
 #define fileName "gct"
-#define dst ((void*)0x817F0000)
-#define size 0xE000 // 7 blocks
+#define dst ((void*)0x817FA800)
+#define size 0x4000 // 2 blocks
+#define magicAddr (dst+size)
+#define magic 0xabcd1234
 int onReadOptionBlock(TCardManager *this, CARDFileInfo *fileInfo) {
   int rc;
+
+  // if magic is correct -> already loaded -> do not load again
+  if (*(unsigned int*)(magicAddr) == magic) goto orig;
+
   // mount
   if ((rc = mount_(this, 1))) goto orig;
 
@@ -44,7 +52,11 @@ int onReadOptionBlock(TCardManager *this, CARDFileInfo *fileInfo) {
   } else {
     // everything is good => apply gecko code
     // TODO entry
-    ((void(*)())0x817f4000)();
+    // ((void(*)())0x817f4000)();
+    if (*(uint32_t*)(dst) == 0x00d0c0de && *(uint32_t*)(dst+4) == 0x00d0c0de) {
+      // is gct
+      *(uint32_t*)(magicAddr) = magic; // set magic to enable gecko code
+    }
   }
 
   // close file

ReadFile.ld

@@ -1,4 +1,4 @@
-$$ = 0x817eff00;
+$$ = 0;
 
 /* TCardManager::cmdLoop() */
-$bl$onReadOptionBlock = 0x801069f4;
+$C2$onReadOptionBlock = 0x801069f4;

gecko-gosub.s

@@ -0,0 +1,10 @@
+.set dst, 0x817fa800
+
+## backup r15 (pointer to current gecko instruction) at dst-4
+  add r0, r15, r4
+  lis r3, dst-4@ha
+  stwu r0, dst-4@l(r3)
+## update r15 = dst + 8(header) - r4(this C0 code size)
+  addi r15, r3, 4+8
+  sub r15, r15, r4
+  blr

gecko-return.s

@@ -0,0 +1,8 @@
+.set dst, 0x817fa800
+
+## restore r15 (pointer to current gecko instruction) from dst-4
+  lis r3, dst-4@ha
+  lwz r15, dst-4@l(r3)
+## update r15 = restored r15 - r4(this C0 code size)
+  sub r15, r15, r4
+  blr