libpayload: Rework exception hook interface

This patch makes some slight changes to the exception hook interface.
The old code provides a different handler hook for every exception
type... however, in practice all those hook functions often need to look
very similar, so this creates more boilerplate than it removes. The new
interface just allows for a single hook with the exception type passed
as an argument, and the consumer can signal whether the exception was
handled through the return value. (Right now this still only supports
one consumer, but it could easily be extended to walk through a list of
hooks if the need arises.)

Also move the excepton state from an argument to a global. This avoids a
lot of boilerplate since some consumers need to change the state from
many places, so they would have to pass the same pointer around many
times. It also removes the false suggestion that the exception state was
not global and you could have multiple copies of it (which the exception
core doesn't support for any architecture).

On the ARM side, the exception state is separated from the exception
stack for easier access. (This requires some assembly changes, and I
threw in a few comments and corrected the immediate sigils from '$' to
the official '#' while I'm there.) Since the exception state is now both
stored and loaded through an indirection pointer, this allows for some
very limited reentrance (you could point it to a different struct while
handling an exception, and while you still won't be able to return to
the outer-level exception from there, you could at least swap out the
pointer and return back to System Mode in one go).

BUG=chrome-os-partner:18390
TEST=Made sure normal exceptions still get dumped correctly on both
archs.

Original-Change-Id: I5d9a934fab7c14ccb2c9d7ee4b3465c825521fa2
Original-Signed-off-by: Julius Werner <jwerner@chromium.org>
Original-Reviewed-on: https://chromium-review.googlesource.com/202562
Original-Reviewed-by: Stefan Reinauer <reinauer@chromium.org>
(cherry picked from commit 97542110f0b385b9b8d89675866e65db8ca32aeb)
Signed-off-by: Marc Jones <marc.jones@se-eng.com>

*** Squashed to prevent build failures. ***

libpayload: align arm64 with new exception handling model

The exception handling was previously updated, however the
arm64 changes raced with hat one. Make the arm64 align with
the new model. Without these changes compilation will fail.

BUG=None
BRANCH=None
TEST=Can build libpayload for rush.

Original-Change-Id: I320b39a57b985d1f87446ea7757955664f8dba8f
Original-Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Original-Reviewed-on: https://chromium-review.googlesource.com/204402
Original-Reviewed-by: Furquan Shaikh <furquan@chromium.org>
Original-Commit-Queue: Furquan Shaikh <furquan@chromium.org>
(cherry picked from commit 0080df41b311ef20f9214b386fa4e38ee54aa1a1)
Signed-off-by: Marc Jones <marc.jones@se-eng.com>

Change-Id: I9a0bb3848cf5286f9f4bb08172a9f4a15278348e
Reviewed-on: http://review.coreboot.org/8117
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>

2 files changed, 57 insertions, 65 deletions

diff --git a/payloads/libpayload/arch/arm/exception.c b/payloads/libpayload/arch/arm/exception.c
index 45b77a7460..d100937295 100644
--- a/payloads/libpayload/arch/arm/exception.c
+++ b/payloads/libpayload/arch/arm/exception.c
@@ -33,22 +33,17 @@
 #include <libpayload.h>
 #include <stdint.h>
 
-uint8_t exception_stack[0x1000] __attribute__((aligned(8)));
-extern void *exception_stack_end;
+u32 exception_stack[0x400] __attribute__((aligned(8)));
+struct exception_state exception_state;
 
-struct exception_handler_info
-{
-	const char *name;
-	exception_hook hook;
-};
-
-static struct exception_handler_info exceptions[EXC_COUNT] = {
-	[EXC_UNDEF]  = { "_undefined_instruction" },
-	[EXC_SWI]    = { "_software_interrupt" },
-	[EXC_PABORT] = { "_prefetch_abort" },
-	[EXC_DABORT] = { "_data_abort" },
-	[EXC_IRQ]    = { "_irq" },
-	[EXC_FIQ]    = { "_fiq" },
+static exception_hook hook;
+static const char *names[EXC_COUNT] = {
+	[EXC_UNDEF]  = "Undefined Instruction",
+	[EXC_SWI]    = "Software Interrupt",
+	[EXC_PABORT] = "Prefetch Abort",
+	[EXC_DABORT] = "Data Abort",
+	[EXC_IRQ]    = "Interrupt",
+	[EXC_FIQ]    = "Fast Interrupt",
 };
 
 static void dump_stack(uintptr_t addr, size_t bytes)
@@ -66,7 +61,7 @@ static void dump_stack(uintptr_t addr, size_t bytes)
 	}
 }
 
-static void print_regs(struct exception_state *state)
+static void print_regs(void)
 {
 	int i;
 
@@ -81,30 +76,21 @@ static void print_regs(struct exception_state *state)
 			printf("IP");
 		else
 			printf("R%d", i);
-		printf(" = 0x%08x\n", state->regs[i]);
+		printf(" = 0x%08x\n", exception_state.regs[i]);
 	}
-	printf("CPSR = 0x%08x\n", state->cpsr);
+	printf("CPSR = 0x%08x\n", exception_state.cpsr);
 }
 
-void exception_dispatch(struct exception_state *state, int idx);
-void exception_dispatch(struct exception_state *state, int idx)
+void exception_dispatch(u32 idx)
 {
-	if (idx >= EXC_COUNT) {
-		printf("Bad exception index %d.\n", idx);
-	} else {
-		struct exception_handler_info *info = &exceptions[idx];
-		if (info->hook) {
-			info->hook(idx, state);
-			return;
-		}
+	die_if(idx >= EXC_COUNT || !names[idx], "Bad exception index %u!", idx);
 
-		if (info->name)
-			printf("exception %s\n", info->name);
-		else
-			printf("exception _not_used.\n");
-	}
-	print_regs(state);
-	dump_stack(state->regs[13], 512);
+	if (hook && hook(idx))
+		return;
+
+	printf("%s Exception\n", names[idx]);
+	print_regs();
+	dump_stack(exception_state.regs[13], 512);
 	halt();
 }
 
@@ -119,11 +105,13 @@ void exception_init(void)
 
 	extern uint32_t exception_table[];
 	set_vbar((uintptr_t)exception_table);
-	exception_stack_end = exception_stack + sizeof(exception_stack);
+
+	exception_stack_end = exception_stack + ARRAY_SIZE(exception_stack);
+	exception_state_ptr = &exception_state;
 }
 
-void exception_install_hook(int type, exception_hook hook)
+void exception_install_hook(exception_hook h)
 {
-	die_if(type >= EXC_COUNT, "Out of bounds exception index %d.\n", type);
-	exceptions[type].hook = hook;
+	die_if(hook, "Implement support for a list of hooks if you need it.");
+	hook = h;
 }
diff --git a/payloads/libpayload/arch/arm/exception_asm.S b/payloads/libpayload/arch/arm/exception_asm.S
index 7b722cb86f..8715955de2 100644
--- a/payloads/libpayload/arch/arm/exception_asm.S
+++ b/payloads/libpayload/arch/arm/exception_asm.S
@@ -43,72 +43,76 @@ exception_table:
 	b	8f
 
 1:
-	mov	sp, $0
+	mov	sp, #0
 	b	exception_common
 
 /* Undefined Instruction (CAREFUL: the PC offset is specific to thumb mode!) */
 2:
-	sub	lr, lr, $2
-	mov	sp, $1
+	sub	lr, lr, #2
+	mov	sp, #1
 	b	exception_common
 
 /* Software Interrupt (no PC offset necessary) */
 3:
-	mov	sp, $2
+	mov	sp, #2
 	b	exception_common
 
 /* Prefetch Abort */
 4:
-	sub	lr, lr, $4
-	mov	sp, $3
+	sub	lr, lr, #4
+	mov	sp, #3
 	b	exception_common
 
 /* Data Abort */
 5:
-	sub	lr, lr, $8
-	mov	sp, $4
+	sub	lr, lr, #8
+	mov	sp, #4
 	b	exception_common
 
 /* (not used) */
 6:
-	mov	sp, $5
+	mov	sp, #5
 	b	exception_common
 
 /* Interrupt */
 7:
-	sub	lr, lr, $4
-	mov	sp, $6
+	sub	lr, lr, #4
+	mov	sp, #6
 	b	exception_common
 
 /* Fast Interrupt */
 8:
-	sub	lr, lr, $4
-	mov	sp, $7
+	sub	lr, lr, #4
+	mov	sp, #7
 	b	exception_common
 
 exception_common:
 	str	sp, exception_idx
-	ldr	sp, exception_stack_end
-	push	{ lr }
-	stmfd	sp, { sp, lr }^
-	sub	sp, sp, $8
-	push	{ r0 - r12 }
+	ldr	sp, exception_state_ptr
+	stmia	sp!, { r0 - r12 }	/* Save regs from bottom to top */
+	stmia	sp, { sp, lr }^		/* Save banked SP/LR (no writeback) */
+	str	lr, [sp, #(4 * 2)]	/* Save PC to &regs[13] + 2 */
 	mrs	r0, SPSR
-	push	{ r0 }
-	mov	r0, sp
-	ldr	r1, exception_idx
+	str	r0, [sp, #(4 * 3)]	/* Save SPSR to &regs[13] + 3 */
+	ldr	sp, exception_stack_end	/* Point SP to the stack for C code */
+	ldr	r0, exception_idx
 	blx	exception_dispatch
-	pop	{ r0 }
-	msr	SPSR_cxsf, r0
-	pop	{ r0 - r12 }
-	add	sp, sp, $8
-	ldmfd	sp!, { pc }^
+	ldr	sp, exception_state_ptr
+	ldr	r0, [sp, #(4 * 16)]	/* Load SPSR from &regs[0] + 16... */
+	msr	SPSR_cxsf, r0		/* ...and get it out of the way */
+	ldmia	sp!, { r0 - r12 }	/* Restore regs from bottom to top */
+	ldmia	sp, { sp, lr }^		/* Restore SP/LR to banked location */
+	add	sp, sp, #8		/* Adjust SP (no writeback allowed) */
+	ldmia	sp!, { pc }^		/* Do exception return (mode switch) */
 
 
 	.align 2
 	.global exception_stack_end
 exception_stack_end:
 	.word 0
+	.global exception_state_ptr
+exception_state_ptr:
+	.word 0
 
 exception_idx:
 	.word 0