arch/arm64/kernel/exceptions.c


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/* SPDX-License-Identifier: GPL-2.0+ */
/*
 * exceptions.c - report an abort through the console before parking,
 * so a firmware handoff bug says why it died instead of hanging quiet.
 * ESR/FAR decode follows armv8 DDI 0487, the EC and ISS fields.
 *
 * Copyright (C) 2026 Bradley Morgan <brads@mainlining.org>
 */

#include <stdint.h>
#include <debug.h>

struct exc_frame {
	uint64_t esr;
	uint64_t far;
	uint64_t lr;
};

/*
 * exception class from ESR, bits 31:26. the classes a bootloader can
 * actually hit with any frequency.
 */
static const char *exc_class_str(uint64_t esr)
{
	switch (esr >> 26) {
	case 0x04:	return "data abort, lower EL";
	case 0x05:	return "data abort, same EL";
	case 0x25:	return "data abort, same EL";
	case 0x08:	return "stack pointer misaligned";
	case 0x11:	return "instruction abort, same EL";
	case 0x16:	return "SError";
	case 0x1a:	return "unhandled exception";
	case 0x22:	return "pc alignment fault";
	case 0x24:	return "unknown trap";
	case 0x26:	return "same EL exception return";
	default:	return "unknown EC";
	}
}

/*
 * far is only meaningful for the abort and alignment classes, note it
 * for those and skip it otherwise so the report does not mislead.
 */
static int exc_far_valid(uint64_t esr)
{
	switch (esr >> 26) {
	case 0x04:
	case 0x05:
	case 0x25:
	case 0x11:
	case 0x22:
		return 1;
	default:
		return 0;
	}
}

void exc_report(uint64_t esr, uint64_t far, uint64_t lr)
{
	dprintf(CRITICAL, "tashaboot: exception %s\n", exc_class_str(esr));
	dprintf(CRITICAL, "esr %016llx lr %016llx\n",
		(unsigned long long)esr, (unsigned long long)lr);
	if (exc_far_valid(esr))
		dprintf(CRITICAL, "far %016llx\n", (unsigned long long)far);

	/* nothing recovers from an abort here, park after reporting */
}