libpayload: arm64: Make exception handling closer to arm32

This patch reworks the arm64 exception handling to be more similar to
how it works on arm32. This includes a bunch of features like actually
saving and restoring more exception state in the exception_state
structure and supporting the same sort of partial reentrancy that is
useful for GDB. Since there's no instruction to directly load into or
store out of SP on arm64, we can't do quite the same thing where we use
that to read an exception_state_ptr variable right after exception entry
when no other register is available. But we can do something very
similar by (ab-)using the "high" stack pointer (SP_EL2) as a pointer to
the exception_state struct and providing a function to change it.

Change-Id: Ia16a1124be1824392a309ae1f4cb031547d184c1
Signed-off-by: Julius Werner <jwerner@chromium.org>
Reviewed-on: https://review.coreboot.org/29018
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>

1 files changed, 8 insertions, 7 deletions

diff --git a/payloads/libpayload/arch/arm64/exception.c b/payloads/libpayload/arch/arm64/exception.c
index a84daf1563..a5e55163a8 100644
--- a/payloads/libpayload/arch/arm64/exception.c
+++ b/payloads/libpayload/arch/arm64/exception.c
@@ -31,6 +31,8 @@
 #include <libpayload.h>
 #include <stdint.h>
 
+u64 exception_stack[0x200] __attribute__((aligned(16)));
+u64 *exception_stack_end = exception_stack + ARRAY_SIZE(exception_stack);
 extern unsigned int test_exc;
 
 struct exception_handler_info
@@ -39,7 +41,7 @@ struct exception_handler_info
 };
 
 static exception_hook hook;
-struct exception_state *exception_state;
+struct exception_state exception_state;
 
 static struct exception_handler_info exceptions[EXC_COUNT] = {
 	[EXC_SYNC_SP0] = { "_sync_sp_el0" },
@@ -88,14 +90,12 @@ static void print_regs(struct exception_state *state)
 		       i, state->regs[i], i + 1, state->regs[i + 1]);
 	}
 	printf("X30 = 0x%016llx          SP = 0x%016llx\n",
-	       state->regs[30], raw_read_sp_el0());
+	       state->regs[30], state->sp);
 }
 
 void exception_dispatch(struct exception_state *state, int idx);
 void exception_dispatch(struct exception_state *state, int idx)
 {
-	exception_state = state;
-
 	if (idx >= EXC_COUNT) {
 		printf("Bad exception index %d.\n", idx);
 	} else {
@@ -110,7 +110,7 @@ void exception_dispatch(struct exception_state *state, int idx)
 	}
 	print_regs(state);
 	/* Few words below SP in case we need state from a returned function. */
-	dump_stack(raw_read_sp_el0() - 32, 512);
+	dump_stack(state->sp - 32, 512);
 
 	if (test_exc) {
 		state->elr += 4;
@@ -123,8 +123,9 @@ void exception_dispatch(struct exception_state *state, int idx)
 
 void exception_init(void)
 {
-	extern void* exception_table;
-	set_vbar(&exception_table);
+	extern uint64_t exception_table[];
+	raw_write_vbar_el2((uintptr_t)exception_table);
+	exception_set_state_ptr(&exception_state);
 }
 
 void exception_install_hook(exception_hook h)