arm64/BUG: Use BRK instruction for generic BUG traps

Currently, the minimal default BUG() implementation from asm-
generic is used for arm64.

This patch uses the BRK software breakpoint instruction to generate
a trap instead, similarly to most other arches, with the generic
BUG code generating the dmesg boilerplate.

This allows bug metadata to be moved to a separate table and
reduces the amount of inline code at BUG and WARN sites.  This also
avoids clobbering any registers before they can be dumped.

To mitigate the size of the bug table further, this patch makes
use of the existing infrastructure for encoding addresses within
the bug table as 32-bit offsets instead of absolute pointers.
(Note that this limits the kernel size to 2GB.)

Traps are registered at arch_initcall time for aarch64, but BUG
has minimal real dependencies and it is desirable to be able to
generate bug splats as early as possible.  This patch redirects
all debug exceptions caused by BRK directly to bug_handler() until
the full debug exception support has been initialised.

Signed-off-by: Dave Martin <Dave.Martin@arm.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

1 files changed, 64 insertions, 0 deletions

diff --git a/arch/arm64/include/asm/bug.h b/arch/arm64/include/asm/bug.h
new file mode 100644
index 000000000000..4a748ce9ba1a
--- /dev/null
+++ b/arch/arm64/include/asm/bug.h
@@ -0,0 +1,64 @@
+/*
+ * Copyright (C) 2015  ARM Limited
+ * Author: Dave Martin <Dave.Martin@arm.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef _ARCH_ARM64_ASM_BUG_H
+#define _ARCH_ARM64_ASM_BUG_H
+
+#include <asm/debug-monitors.h>
+
+#ifdef CONFIG_GENERIC_BUG
+#define HAVE_ARCH_BUG
+
+#ifdef CONFIG_DEBUG_BUGVERBOSE
+#define _BUGVERBOSE_LOCATION(file, line) __BUGVERBOSE_LOCATION(file, line)
+#define __BUGVERBOSE_LOCATION(file, line)				\
+		".pushsection .rodata.str,\"aMS\",@progbits,1\n"	\
+	"2:	.string \"" file "\"\n\t"				\
+		".popsection\n\t"					\
+									\
+		".long 2b - 0b\n\t"					\
+		".short " #line "\n\t"
+#else
+#define _BUGVERBOSE_LOCATION(file, line)
+#endif
+
+#define _BUG_FLAGS(flags) __BUG_FLAGS(flags)
+
+#define __BUG_FLAGS(flags) asm volatile (		\
+		".pushsection __bug_table,\"a\"\n\t"	\
+		".align 2\n\t"				\
+	"0:	.long 1f - 0b\n\t"			\
+_BUGVERBOSE_LOCATION(__FILE__, __LINE__)		\
+		".short " #flags "\n\t"			\
+		".popsection\n"				\
+							\
+	"1:	brk %[imm]"				\
+		:: [imm] "i" (BUG_BRK_IMM)		\
+)
+
+#define BUG() do {				\
+	_BUG_FLAGS(0);				\
+	unreachable();				\
+} while (0)
+
+#define __WARN_TAINT(taint) _BUG_FLAGS(BUGFLAG_TAINT(taint))
+
+#endif /* ! CONFIG_GENERIC_BUG */
+
+#include <asm-generic/bug.h>
+
+#endif /* ! _ARCH_ARM64_ASM_BUG_H */