arm64: Add ASM_BUG()

Currently. we can only use BUG() from C code, though there are
situations where we would like an equivalent mechanism in assembly code.

This patch refactors our BUG() definition such that it can be used in
either C or assembly, in the form of a new ASM_BUG().

The refactoring requires the removal of escape sequences, such as '\n'
and '\t', but these aren't strictly necessary as we can use ';' to
terminate assembler statements.

The low-level assembly is factored out into <asm/asm-bug.h>, with
<asm/bug.h> retained as the C wrapper.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Dave Martin <dave.martin@arm.com>
Cc: James Morse <james.morse@arm.com>
Cc: Will Deacon <will.deacon@arm.com>

arch/arm64/include/asm/asm-bug.h

@@ -0,0 +1,54 @@
+#ifndef __ASM_ASM_BUG_H
+/*
+ * Copyright (C) 2017  ARM Limited
+ *
+ * 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/>.
+ */
+#define __ASM_ASM_BUG_H
+
+#include <asm/brk-imm.h>
+
+#ifdef CONFIG_DEBUG_BUGVERBOSE
+#define _BUGVERBOSE_LOCATION(file, line) __BUGVERBOSE_LOCATION(file, line)
+#define __BUGVERBOSE_LOCATION(file, line)			\
+		.pushsection .rodata.str,"aMS",@progbits,1;	\
+	2:	.string file;					\
+		.popsection;					\
+								\
+		.long 2b - 0b;					\
+		.short line;
+#else
+#define _BUGVERBOSE_LOCATION(file, line)
+#endif
+
+#ifdef CONFIG_GENERIC_BUG
+
+#define __BUG_ENTRY(flags) 				\
+		.pushsection __bug_table,"aw";		\
+		.align 2;				\
+	0:	.long 1f - 0b;				\
+_BUGVERBOSE_LOCATION(__FILE__, __LINE__)		\
+		.short flags; 				\
+		.popsection;				\
+	1:
+#else
+#define __BUG_ENTRY(flags)
+#endif
+
+#define ASM_BUG_FLAGS(flags)				\
+	__BUG_ENTRY(flags)				\
+	brk	BUG_BRK_IMM
+
+#define ASM_BUG()	ASM_BUG_FLAGS(0)
+
+#endif /* __ASM_ASM_BUG_H */