kernel: tentative stack overflow panic, 14 kiB stack on G-III

I saw a crash with the 12 kB stack. Added an error message to diagnose
further similar issues, and bumbed the stack to 14 kB. That's a lot of
space just for BFile but stability is queen... :x

src/kernel/exch.c

@@ -50,6 +50,7 @@ GNORETURN static void gint_default_panic(GUNUSED uint32_t code)
 	if(code == 0x1020) name = "DMA address error";
 	if(code == 0x1040) name = "Add-in too large";
 	if(code == 0x1060) name = "Memory init failed";
+	if(code == 0x1080) name = "Stack overflow";
 
 	if(name[0]) dtext(1, 9, name);
 	else dprint(1, 9, "%03x", code);
@@ -82,6 +83,7 @@ GNORETURN static void gint_default_panic(GUNUSED uint32_t code)
 	if(code == 0x1020) name = "DMA address error";
 	if(code == 0x1040) name = "Add-in not fully mapped (too large)";
 	if(code == 0x1060) name = "Memory initialization failed (heap)";
+	if(code == 0x1080) name = "Stack overflow during world switch";
 
 	dprint(6, 25, "%03x %s", code, name);
 

src/kernel/kernel.c

@@ -9,6 +9,7 @@
 #include <gint/mpu/intc.h>
 #include <gint/kmalloc.h>
 #include <gint/cpu.h>
+#include <gint/exc.h>
 
 #include <string.h>
 #include <stdlib.h>
@@ -28,6 +29,9 @@ gint_world_t gint_world_addin = NULL;
 /* Dynamic flags for all drivers */
 uint8_t *gint_driver_flags = NULL;
 
+/* Top of the stack */
+void *gint_stack_top = NULL;
+
 //---
 //	Initialization and unloading
 //---
@@ -45,9 +49,12 @@ void kinit(void)
 	   expanded region. */
 	uint32_t uram_end = (uint32_t)mmu_uram() + mmu_uram_size();
 
-	/* Stack space on SH4. 12 kB is a lot, but BFile is known to overflow
+	/* Stack space on SH4. 14 kB is a lot, but Fugue's BFile has been seen
-	   from the previous 8 kB design */
+	   overflowing both 8 kB and 12 kB */
-	if(isSH4()) uram_end -= 0x3000;
+	if(isSH4()) {
+		uram_end -= (gint[HWFS] == HWFS_FUGUE) ? 0x3800 : 0x2000;
+		gint_stack_top = (void *)uram_end;
+	}
 
 	/* VBR is advanced 0x100 bytes because of an unused gap */
 	uram_end -= (isSH3() ? 0x600 : 0x1100);
@@ -61,6 +68,7 @@ void kinit(void)
 	   leave 16 kB. */
 	VBR = (uint32_t)mmu_uram();
 	uint32_t uram_end = (uint32_t)mmu_uram() + mmu_uram_size() - 0x4000;
+	gint_stack_top = (void *)uram_end;
 	#endif
 
 	/* Event handler entry points */
@@ -93,10 +101,7 @@ void kinit(void)
 	gint_driver_flags = malloc(gint_driver_count());
 
 	if(!gint_world_os || !gint_world_addin || !gint_driver_flags)
-	{
-		extern void gint_panic(uint32_t code);
 		gint_panic(0x1060);
-	}
 
 	/* Initialize drivers */
 	for(int i = 0; i < gint_driver_count(); i++)

src/kernel/world.c

@@ -1,6 +1,7 @@
 #include <gint/drivers.h>
 #include <gint/cpu.h>
 #include <gint/gint.h>
+#include <gint/exc.h>
 #include <gint/defs/call.h>
 
 #include <stdlib.h>
@@ -126,8 +127,24 @@ void gint_world_switch_out(gint_world_t world_addin, gint_world_t world_os)
 
 int gint_world_switch(gint_call_t call)
 {
+	extern void *gint_stack_top;
 	gint_world_switch_out(gint_world_addin, gint_world_os);
+
+	/* Watch out for stack overflows */
+	uint32_t *canary = gint_stack_top;
+	if(canary)
+		*canary = 0xb7c0ffee;
+
 	int rc = call.function ? gint_call(call) : 0;
+
+	/* The canary check needs to occur before switching in the gint world;
+	   otherwise we just crash due to the overflow. gint_panic() isn't
+	   really designed to work from the OS world, but it does fine on the
+	   fx-9860G series and sometimes also on the fx-CG series; better crash
+	   attempting to show a panic message than just crash */
+	if(canary && *canary != 0xb7c0ffee)
+		gint_panic(0x1080);
+
 	gint_world_switch_in(gint_world_os, gint_world_addin);
 	return rc;
 }