interrupts: save caller-saved registers in main handler

This is an obvious requirement for the interrupt routine, which was
forgotten and only surfaced when I used a timer callback started with
multiplications in an innocent add-in. r0..r7 are saved automatically,
which leaves pr, gbr, mach et macl susceptible to corruption by the
interrupt handler.

include/gint/gint.h

@@ -97,21 +97,24 @@ int gint_intlevel(int intid, int level);
    list of event codes and their associated interrupts.
 
    The handler function must be an interrupt handler: it must not raise
-   exceptions, must end with 'rte', and it will use the kernel register bank.
+   exceptions, must end with 'rts', and it will use the kernel register bank.
+   You read that right, it must end with rts because gint's main handler saves
+   registers besides the automated r0..r7. Do *not* use 'rte' in the handler.
    For convenience I allow any block size to be loaded as an interrupt handler,
    but it should really be a multiple of 0x20 bytes and not override other
    handlers. If it's not written in assembler, then you're likely doing
-   something wrong, even with __attribute__((interrupt_handler)).
+   something wrong, especially with __attribute__((interrupt_handler)) which
+   uses rte.
 
    It is common for interrupt handlers to have a few bytes of data, such as the
    address of a callback function. gint often stores this data in the last
-   bytes of the block. This function returns the VBR address of the block to
-   allow the caller to edit the parameters.
+   bytes of the block. This function returns the VBR address of the block which
+   has just been installed, to allow the caller to edit the parameters later.
 
    @event_code  Identifier of the interrupt block
    @handler     Address of handler function
    @size        How many bytes to copy
    Returns the VBR address where the handlers was installed. */
-void *gint_inthandler(int event_code, const void *handler, size_t size);
+void *gint_inthandler(int event_code, void const *handler, size_t size);
 
 #endif /* GINT_GINT */

src/core/exch.c

@@ -3,6 +3,7 @@
 #include <gint/clock.h>
 #include <gint/mpu/dma.h>
 #include <gint/defs/attributes.h>
+#include <gint/hardware.h>
 
 #define dprint(x, y, ...) dprint(x, y, C_BLACK, C_NONE, __VA_ARGS__)
 #define dtext(x, y, str)  dtext (x, y, str, C_BLACK, C_NONE)
@@ -16,6 +17,9 @@ GNORETURN static void gint_default_panic(GUNUSED uint32_t code)
 	uint32_t PC;
 	__asm__("stc spc, %0" : "=r"(PC));
 
+	uint32_t SGR = 0xffffffff;
+	if(isSH4()) __asm__("stc sgr, %0" : "=r"(SGR));
+
 	dfont(NULL);
 	dclear(C_WHITE);
 
@@ -42,6 +46,7 @@ GNORETURN static void gint_default_panic(GUNUSED uint32_t code)
 	dprint(1, 17, " PC :%08x", PC);
 	dprint(1, 25, "TEA :%08x", TEA);
 	dprint(1, 33, "TRA :%08x", TRA);
+	if(isSH4()) dprint(1, 41, "SGR :%08x", SGR);
 
 	dtext(1, 49, "The add-in crashed.");
 	dtext(1, 57, "Please reset the calc");

src/core/gint.c

@@ -58,6 +58,6 @@ void *gint_inthandler(int event_code, const void *handler, size_t size)
 	/* Prevent overriding the entry gate */
 	if(event_code < 0) return NULL;
 
-	void *dest = (void *)&gint_vbr + event_code + 0x620;
+	void *dest = (void *)&gint_vbr + event_code + 0x640;
 	return memcpy(dest, handler, size);
 }

src/core/inth.S

@@ -54,9 +54,16 @@ _gint_inth_7305:
 1:	.long	0xff000028
 #endif
 
-/* SH7305-TYPE INTERRUPT HANDLER ENTRY - 20 BYTES */
+/* SH7305-TYPE INTERRUPT HANDLER ENTRY - 40 BYTES */
 
 _gint_inth_7305:
+	/* Save caller-saved registers which might currently be in use by the
+	   interrupted function, as we don't know what the callback will do */
+	sts.l	pr, @-r15
+	stc.l	gbr, @-r15
+	sts.l	mach, @-r15
+	sts.l	macl, @-r15
+
 	/* Get the event code from the INTEVT register */
 	mov.l	1f, r0
 	mov.l	@r0, r0
@@ -66,19 +73,34 @@ _gint_inth_7305:
 	shll8	r1
 	sub	r1, r0
 
-	/* Add the distance to the first entry and jump */
-	add	#16, r0
-	braf	r0
+	/* Add the distance to the first entry and jump as a subroutine */
+	add	#40, r0
+	bsrf	r0
 	nop
 
-	.zero	12
+	/* Restore caller-saved registers */
+	lds.l	@r15+, macl
+	lds.l	@r15+, mach
+	ldc.l	@r15+, gbr
+	lds.l	@r15+, pr
+
+	rte
+	nop
+
+	.zero	24
 1:	.long	0xff000028
 
 #ifdef FX9860G
 
-/* SH7705-TYPE INTERRUT HANDLER ENTRY - 32 BYTES */
+/* SH7705-TYPE INTERRUT HANDLER ENTRY - 52 BYTES */
 
 _gint_inth_7705:
+	/* Save caller-saved registers as before */
+	sts.l	pr, @-r15
+	stc.l	gbr, @-r15
+	sts.l	mach, @-r15
+	sts.l	macl, @-r15
+
 	/* Get the event code from the INTEVT2 register */
 	mov.l	1f, r0
 	mov.l	@r0, r0		/* r0 = old_code */
@@ -93,10 +115,20 @@ _gint_inth_7705:
 	shld	r3, r0		/* r0 = new_code - 0x400 */
 
 	/* Add the distance between nop and the first entry, and jump */
-	add	#8, r0
-	braf	r0
+	add	#32, r0
+	bsrf	r0
 	nop
 
+	/* Restore saved registers */
+	lds.l	@r15+, mach
+	lds.l	@r15+, macl
+	ldc.l	@r15+, gbr
+	lds.l	@r15+, pr
+
+	rte
+	nop
+
+	.zero 12
 1:	.long	0xa4000000	/* INTEVT2 register */
 2:	.long	_inth_remap
 

src/core/setup.c

@@ -85,7 +85,7 @@ void gint_install(void)
 	/* Load the event handler entry points into memory */
 	memcpy(vbr + 0x100, gint_exch_tlbh, exch_tlbh_size);
 	memcpy(vbr + 0x400, gint_exch_tlbh, exch_tlbh_size);
-	memcpy(vbr + 0x600, inth_entry, 32);
+	memcpy(vbr + 0x600, inth_entry, 64);
 
 	/* Time to switch VBR and roll! */
 	system_vbr = gint_setvbr((uint32_t)vbr, lock);

src/dma/inth.s

@@ -25,7 +25,7 @@ _inth_dma_te:
 	and	r2, r0
 	mov.w	r0, @r1
 
-	rte
+	rts
 	nop
 
 1:	.long 0			/* CHCR, set dynamically */

src/rtc/inth.s

@@ -54,7 +54,7 @@ _inth_rtc_pri_helper:
 
 .end:
 	lds.l	@r15+, pr
-	rte
+	rts
 	nop
 
 	.zero 8

src/tmu/inth.s

@@ -81,7 +81,7 @@ _inth_tmu_1:
 
 .end:
 	lds.l	@r15+, pr
-	rte
+	rts
 	nop
 
 	.zero	12
@@ -176,7 +176,7 @@ _inth_etmu_help:
 	nop
 
 	lds.l	@r15+, pr
-	rte
+	rts
 	nop
 
 	.zero	18
@@ -199,10 +199,10 @@ _inth_etmux:
 
 	/* Offset from VBR where extra timer 2 is located:
 	   - 0x600 to reach the interrupt handlers
-	   - 0x020 to jump over the entry gate
+	   - 0x040 to jump over the entry gate
 	   - 0x840 to reach the handler of ETMU2
 	   - 0x004 to skip its first instructions (the size is hardcoded) */
-1:	.long	0xe64
+1:	.long	0xe84
 
 .id_etmux:
 	.long	0		/* Timer ID */