x86/unwind: Add the ORC unwinder

Add the new ORC unwinder which is enabled by CONFIG_ORC_UNWINDER=y.
It plugs into the existing x86 unwinder framework.

It relies on objtool to generate the needed .orc_unwind and
.orc_unwind_ip sections.

For more details on why ORC is used instead of DWARF, see
Documentation/x86/orc-unwinder.txt - but the short version is
that it's a simplified, fundamentally more robust debugninfo
data structure, which also allows up to two orders of magnitude
faster lookups than the DWARF unwinder - which matters to
profiling workloads like perf.

Thanks to Andy Lutomirski for the performance improvement ideas:
splitting the ORC unwind table into two parallel arrays and creating a
fast lookup table to search a subset of the unwind table.

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Jiri Slaby <jslaby@suse.cz>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: live-patching@vger.kernel.org
Link: http://lkml.kernel.org/r/0a6cbfb40f8da99b7a45a1a8302dc6aef16ec812.1500938583.git.jpoimboe@redhat.com
[ Extended the changelog. ]
Signed-off-by: Ingo Molnar <mingo@kernel.org>

include/asm-generic/vmlinux.lds.h

@@ -680,6 +680,31 @@
 #define BUG_TABLE
 #endif
 
+#ifdef CONFIG_ORC_UNWINDER
+#define ORC_UNWIND_TABLE						\
+	. = ALIGN(4);							\
+	.orc_unwind_ip : AT(ADDR(.orc_unwind_ip) - LOAD_OFFSET) {	\
+		VMLINUX_SYMBOL(__start_orc_unwind_ip) = .;		\
+		KEEP(*(.orc_unwind_ip))					\
+		VMLINUX_SYMBOL(__stop_orc_unwind_ip) = .;		\
+	}								\
+	. = ALIGN(6);							\
+	.orc_unwind : AT(ADDR(.orc_unwind) - LOAD_OFFSET) {		\
+		VMLINUX_SYMBOL(__start_orc_unwind) = .;			\
+		KEEP(*(.orc_unwind))					\
+		VMLINUX_SYMBOL(__stop_orc_unwind) = .;			\
+	}								\
+	. = ALIGN(4);							\
+	.orc_lookup : AT(ADDR(.orc_lookup) - LOAD_OFFSET) {		\
+		VMLINUX_SYMBOL(orc_lookup) = .;				\
+		. += (((SIZEOF(.text) + LOOKUP_BLOCK_SIZE - 1) /	\
+			LOOKUP_BLOCK_SIZE) + 1) * 4;			\
+		VMLINUX_SYMBOL(orc_lookup_end) = .;			\
+	}
+#else
+#define ORC_UNWIND_TABLE
+#endif
+
 #ifdef CONFIG_PM_TRACE
 #define TRACEDATA							\
 	. = ALIGN(4);							\
@@ -866,7 +891,7 @@
 		DATA_DATA						\
 		CONSTRUCTORS						\
 	}								\
-	BUG_TABLE
+	BUG_TABLE							\
 
 #define INIT_TEXT_SECTION(inittext_align)				\
 	. = ALIGN(inittext_align);					\