x86/kconfig: Consolidate unwinders into multiple choice selection

There are three mutually exclusive unwinders.  Make that more obvious by
combining them into a multiple-choice selection:

  CONFIG_FRAME_POINTER_UNWINDER
  CONFIG_ORC_UNWINDER
  CONFIG_GUESS_UNWINDER (if CONFIG_EXPERT=y)

Frame pointers are still the default (for now).

The old CONFIG_FRAME_POINTER option is still used in some
arch-independent places, so keep it around, but make it
invisible to the user on x86 - it's now selected by
CONFIG_FRAME_POINTER_UNWINDER=y.

Suggested-by: Ingo Molnar <mingo@kernel.org>
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/20170725135424.zukjmgpz3plf5pmt@treble
Signed-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/Kconfig

@@ -73,7 +73,6 @@ config X86
 	select ARCH_USE_QUEUED_RWLOCKS
 	select ARCH_USE_QUEUED_SPINLOCKS
 	select ARCH_WANT_BATCHED_UNMAP_TLB_FLUSH
-	select ARCH_WANT_FRAME_POINTERS
 	select ARCH_WANTS_DYNAMIC_TASK_STRUCT
 	select ARCH_WANTS_THP_SWAP		if X86_64
 	select BUILDTIME_EXTABLE_SORT
@@ -168,7 +167,7 @@ config X86
 	select HAVE_PERF_REGS
 	select HAVE_PERF_USER_STACK_DUMP
 	select HAVE_REGS_AND_STACK_ACCESS_API
-	select HAVE_RELIABLE_STACKTRACE		if X86_64 && FRAME_POINTER && STACK_VALIDATION
+	select HAVE_RELIABLE_STACKTRACE		if X86_64 && FRAME_POINTER_UNWINDER && STACK_VALIDATION
 	select HAVE_STACK_VALIDATION		if X86_64
 	select HAVE_SYSCALL_TRACEPOINTS
 	select HAVE_UNSTABLE_SCHED_CLOCK

arch/x86/Kconfig.debug

@@ -355,9 +355,32 @@ config PUNIT_ATOM_DEBUG
 	  The current power state can be read from
 	  /sys/kernel/debug/punit_atom/dev_power_state
 
+choice
+	prompt "Choose kernel unwinder"
+	default FRAME_POINTER_UNWINDER
+	---help---
+	  This determines which method will be used for unwinding kernel stack
+	  traces for panics, oopses, bugs, warnings, perf, /proc/<pid>/stack,
+	  livepatch, lockdep, and more.
+
+config FRAME_POINTER_UNWINDER
+	bool "Frame pointer unwinder"
+	select FRAME_POINTER
+	---help---
+	  This option enables the frame pointer unwinder for unwinding kernel
+	  stack traces.
+
+	  The unwinder itself is fast and it uses less RAM than the ORC
+	  unwinder, but the kernel text size will grow by ~3% and the kernel's
+	  overall performance will degrade by roughly 5-10%.
+
+	  This option is recommended if you want to use the livepatch
+	  consistency model, as this is currently the only way to get a
+	  reliable stack trace (CONFIG_HAVE_RELIABLE_STACKTRACE).
+
 config ORC_UNWINDER
 	bool "ORC unwinder"
-	depends on X86_64 && !FRAME_POINTER
+	depends on X86_64
 	select STACK_VALIDATION
 	---help---
 	  This option enables the ORC (Oops Rewind Capability) unwinder for
@@ -371,12 +394,22 @@ config ORC_UNWINDER
 	  Enabling this option will increase the kernel's runtime memory usage
 	  by roughly 2-4MB, depending on your kernel config.
 
-config FRAME_POINTER_UNWINDER
-	def_bool y
-	depends on !ORC_UNWINDER && FRAME_POINTER
-
 config GUESS_UNWINDER
-	def_bool y
+	bool "Guess unwinder"
-	depends on !ORC_UNWINDER && !FRAME_POINTER
+	depends on EXPERT
+	---help---
+	  This option enables the "guess" unwinder for unwinding kernel stack
+	  traces.  It scans the stack and reports every kernel text address it
+	  finds.  Some of the addresses it reports may be incorrect.
+
+	  While this option often produces false positives, it can still be
+	  useful in many cases.  Unlike the other unwinders, it has no runtime
+	  overhead.
+
+endchoice
+
+config FRAME_POINTER
+	depends on !ORC_UNWINDER && !GUESS_UNWINDER
+	bool
 
 endmenu

arch/x86/configs/tiny.config

@@ -1,3 +1,5 @@
 CONFIG_NOHIGHMEM=y
 # CONFIG_HIGHMEM4G is not set
 # CONFIG_HIGHMEM64G is not set
+CONFIG_GUESS_UNWINDER=y
+# CONFIG_FRAME_POINTER_UNWINDER is not set

arch/x86/include/asm/unwind.h

@@ -16,7 +16,7 @@ struct unwind_state {
 	bool signal, full_regs;
 	unsigned long sp, bp, ip;
 	struct pt_regs *regs;
-#elif defined(CONFIG_FRAME_POINTER)
+#elif defined(CONFIG_FRAME_POINTER_UNWINDER)
 	bool got_irq;
 	unsigned long *bp, *orig_sp, ip;
 	struct pt_regs *regs;
@@ -50,7 +50,7 @@ void unwind_start(struct unwind_state *state, struct task_struct *task,
 	__unwind_start(state, task, regs, first_frame);
 }
 
-#if defined(CONFIG_ORC_UNWINDER) || defined(CONFIG_FRAME_POINTER)
+#if defined(CONFIG_ORC_UNWINDER) || defined(CONFIG_FRAME_POINTER_UNWINDER)
 static inline struct pt_regs *unwind_get_entry_regs(struct unwind_state *state)
 {
 	if (unwind_done(state))