linux-kernel - [PATCH v3 10/10] x86/kconfig: make it easier to switch to the new ORC unwinder

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Message-Id: <41b5ab6a98fd73a1521e3defcc1388ee2bbf5fb2.1499786555.git.jpoimboe@redhat.com>
Date:   Tue, 11 Jul 2017 10:33:47 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     x86@...nel.org
Cc:     linux-kernel@...r.kernel.org, live-patching@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andy Lutomirski <luto@...nel.org>, Jiri Slaby <jslaby@...e.cz>,
        Ingo Molnar <mingo@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Mike Galbraith <efault@....de>
Subject: [PATCH v3 10/10] x86/kconfig: make it easier to switch to the new ORC unwinder

A couple of Kconfig changes which make it much easier to switch to the
new CONFIG_ORC_UNWINDER:

1) Remove x86 dependencies on CONFIG_FRAME_POINTER for lockdep,
   latencytop, and fault injection.  x86 has a 'guess' unwinder which
   just scans the stack for kernel text addresses.  It's not 100%
   accurate but in many cases it's good enough.  This allows those users
   who don't want the text overhead of the frame pointer or ORC
   unwinders to still use these features.  More importantly, this also
   makes it much more straightforward to disable frame pointers.

2) Make CONFIG_ORC_UNWINDER depend on !CONFIG_FRAME_POINTER.  While it
   would be possible to have both enabled, it doesn't really make sense
   to do so.  So enforce a sane configuration to prevent the user from
   making a dumb mistake.

With these changes, when you disable CONFIG_FRAME_POINTER, "make
oldconfig" will ask if you want to enable CONFIG_ORC_UNWINDER.

Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>
---
 arch/x86/Kconfig.debug | 7 +++----
 lib/Kconfig.debug      | 6 +++---
 2 files changed, 6 insertions(+), 7 deletions(-)

diff --git a/arch/x86/Kconfig.debug b/arch/x86/Kconfig.debug
index dc10ec6..268a318 100644
--- a/arch/x86/Kconfig.debug
+++ b/arch/x86/Kconfig.debug
@@ -357,7 +357,7 @@ config PUNIT_ATOM_DEBUG
 
 config ORC_UNWINDER
 	bool "ORC unwinder"
-	depends on X86_64
+	depends on X86_64 && !FRAME_POINTER
 	select STACK_VALIDATION
 	---help---
 	  This option enables the ORC (Oops Rewind Capability) unwinder for
@@ -365,9 +365,8 @@ config ORC_UNWINDER
 	  a simplified version of the DWARF Call Frame Information standard.
 
 	  This unwinder is more accurate across interrupt entry frames than the
-	  frame pointer unwinder.  It can also enable a 5-10% performance
-	  improvement across the entire kernel if CONFIG_FRAME_POINTER is
-	  disabled.
+	  frame pointer unwinder.  It also enables a 5-10% performance
+	  improvement across the entire kernel compared to frame pointers.
 
 	  Enabling this option will increase the kernel's runtime memory usage
 	  by roughly 2-4MB, depending on your kernel config.
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index a7abffa..325c1c5 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -1113,7 +1113,7 @@ config LOCKDEP
 	bool
 	depends on DEBUG_KERNEL && TRACE_IRQFLAGS_SUPPORT && STACKTRACE_SUPPORT && LOCKDEP_SUPPORT
 	select STACKTRACE
-	select FRAME_POINTER if !MIPS && !PPC && !ARM_UNWIND && !S390 && !MICROBLAZE && !ARC && !SCORE
+	select FRAME_POINTER if !MIPS && !PPC && !ARM_UNWIND && !S390 && !MICROBLAZE && !ARC && !SCORE && !X86
 	select KALLSYMS
 	select KALLSYMS_ALL
 
@@ -1504,7 +1504,7 @@ config FAULT_INJECTION_STACKTRACE_FILTER
 	depends on FAULT_INJECTION_DEBUG_FS && STACKTRACE_SUPPORT
 	depends on !X86_64
 	select STACKTRACE
-	select FRAME_POINTER if !MIPS && !PPC && !S390 && !MICROBLAZE && !ARM_UNWIND && !ARC && !SCORE
+	select FRAME_POINTER if !MIPS && !PPC && !S390 && !MICROBLAZE && !ARM_UNWIND && !ARC && !SCORE && !X86
 	help
 	  Provide stacktrace filter for fault-injection capabilities
 
@@ -1513,7 +1513,7 @@ config LATENCYTOP
 	depends on DEBUG_KERNEL
 	depends on STACKTRACE_SUPPORT
 	depends on PROC_FS
-	select FRAME_POINTER if !MIPS && !PPC && !S390 && !MICROBLAZE && !ARM_UNWIND && !ARC
+	select FRAME_POINTER if !MIPS && !PPC && !S390 && !MICROBLAZE && !ARM_UNWIND && !ARC && !X86
 	select KALLSYMS
 	select KALLSYMS_ALL
 	select STACKTRACE
-- 
2.7.5