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Subject[tip:x86/asm] x86/kconfig: Consolidate unwinders into multiple choice selection
Commit-ID:  81d387190039c14edac8de2b3ec789beb899afd9
Gitweb: http://git.kernel.org/tip/81d387190039c14edac8de2b3ec789beb899afd9
Author: Josh Poimboeuf <jpoimboe@redhat.com>
AuthorDate: Tue, 25 Jul 2017 08:54:24 -0500
Committer: Ingo Molnar <mingo@kernel.org>
CommitDate: Wed, 26 Jul 2017 14:05:36 +0200

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 | 3 +--
arch/x86/Kconfig.debug | 47 ++++++++++++++++++++++++++++++++++++-------
arch/x86/configs/tiny.config | 2 ++
arch/x86/include/asm/unwind.h | 4 ++--
4 files changed, 45 insertions(+), 11 deletions(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 7ccf26a..9b30212 100644
--- a/arch/x86/Kconfig
+++ b/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
diff --git a/arch/x86/Kconfig.debug b/arch/x86/Kconfig.debug
index 268a318..93bbb31 100644
--- a/arch/x86/Kconfig.debug
+++ b/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
- depends on !ORC_UNWINDER && !FRAME_POINTER
+ bool "Guess unwinder"
+ 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
diff --git a/arch/x86/configs/tiny.config b/arch/x86/configs/tiny.config
index 4b429df..550cd50 100644
--- a/arch/x86/configs/tiny.config
+++ b/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
diff --git a/arch/x86/include/asm/unwind.h b/arch/x86/include/asm/unwind.h
index 25b8d31a..e9f793e 100644
--- a/arch/x86/include/asm/unwind.h
+++ b/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))
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