armv7: Support stack dump after exceptions

This patch enhances the armv7 exception handlers in Coreboot and
libpayload to show the correct SP and LR registers from the aborted
context, and also dump a part of the current stack. Since we cannot
access the banked registers of SVC mode from a different exception mode,
it changes Coreboot (and its payloads) to run in System mode instead. As
both modes can execute all privileged instructions, this should not have
any noticeable effect on firmware operation (please correct me if I'm
wrong!).

Change-Id: I0e04f47619e55308f7da4a3a99c9cae6ae35cc30
Signed-off-by: Julius Werner <jwerner@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/170045
Reviewed-by: Gabe Black <gabeblack@chromium.org>
Reviewed-by: Vincent Palatin <vpalatin@chromium.org>
(cherry picked from commit d0db2f5e938200e3f5899c5e1f1606ab2dd5b334)
Signed-off-by: Isaac Christensen <isaac.christensen@se-eng.com>
Reviewed-on: http://review.coreboot.org/6538
Tested-by: build bot (Jenkins)
Reviewed-by: Ronald G. Minnich <rminnich@gmail.com>

2 files changed, 27 insertions, 7 deletions

diff --git a/payloads/libpayload/arch/armv7/exception.c b/payloads/libpayload/arch/armv7/exception.c
index 9efc312833..8d8b50b175 100644
--- a/payloads/libpayload/arch/armv7/exception.c
+++ b/payloads/libpayload/arch/armv7/exception.c
@@ -43,20 +43,32 @@ void exception_not_used(uint32_t *);
 void exception_irq(uint32_t *);
 void exception_fiq(uint32_t *);
 
+static void dump_stack(uintptr_t addr, size_t bytes)
+{
+	int i, j;
+	const int line = 8;
+	uint32_t *ptr = (uint32_t *)(addr & ~(line * sizeof(*ptr) - 1));
+
+	printf("Dumping stack:\n");
+	for (i = bytes / sizeof(*ptr); i >= 0; i -= line) {
+		printf("%p: ", ptr + i);
+		for (j = i; j < i + line; j++)
+			printf("%08x ", *(ptr + j));
+		printf("\n");
+	}
+}
+
 static void print_regs(uint32_t *regs)
 {
 	int i;
-	/* Don't print the link register and stack pointer since we don't have their
-	 * actual value. They are hidden by the 'shadow' registers provided
-	 * by the trap hardware.
-	 */
+
 	for (i = 0; i < 16; i++) {
 		if (i == 15)
 			printf("PC");
 		else if (i == 14)
-			continue; /* LR */
+			printf("LR");
 		else if (i == 13)
-			continue; /* SP */
+			printf("SP");
 		else if (i == 12)
 			printf("IP");
 		else
@@ -69,6 +81,7 @@ void exception_undefined_instruction(uint32_t *regs)
 {
 	printf("exception _undefined_instruction\n");
 	print_regs(regs);
+	dump_stack(regs[13], 512);
 	halt();
 }
 
@@ -76,6 +89,7 @@ void exception_software_interrupt(uint32_t *regs)
 {
 	printf("exception _software_interrupt\n");
 	print_regs(regs);
+	dump_stack(regs[13], 512);
 	halt();
 }
 
@@ -83,6 +97,7 @@ void exception_prefetch_abort(uint32_t *regs)
 {
 	printf("exception _prefetch_abort\n");
 	print_regs(regs);
+	dump_stack(regs[13], 512);
 	halt();
 }
 
@@ -94,6 +109,7 @@ void exception_data_abort(uint32_t *regs)
 	} else {
 		printf("exception _data_abort\n");
 		print_regs(regs);
+		dump_stack(regs[13], 512);
 	}
 	halt();
 }
@@ -102,6 +118,7 @@ void exception_not_used(uint32_t *regs)
 {
 	printf("exception _not_used\n");
 	print_regs(regs);
+	dump_stack(regs[13], 512);
 	halt();
 }
 
@@ -109,6 +126,7 @@ void exception_irq(uint32_t *regs)
 {
 	printf("exception _irq\n");
 	print_regs(regs);
+	dump_stack(regs[13], 512);
 	halt();
 }
 
@@ -116,6 +134,7 @@ void exception_fiq(uint32_t *regs)
 {
 	printf("exception _fiq\n");
 	print_regs(regs);
+	dump_stack(regs[13], 512);
 	halt();
 }
 
diff --git a/payloads/libpayload/arch/armv7/exception_asm.S b/payloads/libpayload/arch/armv7/exception_asm.S
index e46f4bcf6b..163fdbd52a 100644
--- a/payloads/libpayload/arch/armv7/exception_asm.S
+++ b/payloads/libpayload/arch/armv7/exception_asm.S
@@ -79,6 +79,7 @@ exception_common:
 	str	sp, exception_handler
 	ldr	sp, exception_stack_end
 	push	{ lr }
+	stmfd	sp, { sp, lr }^
 	sub	sp, sp, $8
 	push	{ r0 - r12 }
 	mov	r0, sp
@@ -86,7 +87,7 @@ exception_common:
 	ldr	pc, exception_handler
 	pop	{ r0 - r12 }
 	add	sp, sp, $8
-	ldm	sp!, { pc }^
+	ldmfd	sp!, { pc }^
 
 
 _undefined_instruction:	.word exception_undefined_instruction