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

From: Josh Poimboeuf
Date: Tue Jul 11 2017 - 11:34:31 EST


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@xxxxxxxxxx>
---
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