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arm64: Print a char to UART early in exception handler 

Over time our printk() seems to acquire more and more features... which
is nice, but it also makes it a little less robust when something goes
wrong. If the wrong global is trampled by some buffer overflow, it
suddenly doesn't print anymore. It would be nice to have at least some
way to tell that we triggered a real exception in that case.

With this patch, arm64 exceptions will print a '!' straight to the UART
before trying any of the more fancy printk() stuff. It's not much but it
should tell the difference between an exception and a hang and hopefully
help someone dig in the right direction sooner. This violates loglevels
(which is part of the point), but presumably when you have a fatal
exception you shouldn't care about that anymore.

Change-Id: I3b08ab86beaee55263786011caa5588d93bbc720
Signed-off-by: Julius Werner <jwerner@chromium.org>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/37465
Reviewed-by: Hung-Te Lin <hungte@chromium.org>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
This commit is contained in:
Julius Werner 2019-12-03 23:29:26 -08:00 committed by Patrick Georgi
parent 2e0bca011a
commit 51359d6c84
1 changed files with 8 additions and 2 deletions
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10
src/arch/arm64/armv8/exception.c
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@ -34,6 +34,7 @@
#include <arch/exception.h> #include <arch/exception.h>
#include <arch/transition.h> #include <arch/transition.h>
#include <console/console.h> #include <console/console.h>
#include <console/uart.h>
#include <arch/lib_helpers.h> #include <arch/lib_helpers.h>
uint8_t exception_stack[2*KiB] __attribute__((aligned(16))); uint8_t exception_stack[2*KiB] __attribute__((aligned(16)));
@ -131,8 +132,13 @@ int exception_handler_unregister(uint64_t vid, struct exception_handler *h)
static void print_exception_info(struct exc_state *state, uint64_t idx) static void print_exception_info(struct exc_state *state, uint64_t idx)
{ {
if (idx < NUM_EXC_VIDS) /* Poor man's sign of life in case printk() is shot. */
printk(BIOS_DEBUG, "exception %s\n", exception_names[idx]); __uart_tx_byte('\r');
__uart_tx_byte('\n');
__uart_tx_byte('!');
printk(BIOS_DEBUG, "\nexception %s\n",
idx < NUM_EXC_VIDS ? exception_names[idx] : "_unknown");
print_regs(state); print_regs(state);
/* Few words below SP in case we need state from a returned function. */ /* Few words below SP in case we need state from a returned function. */