[PATCH 4.19 44/56] ARM: 8800/1: use choice for kernel unwinders

Greg Kroah-Hartman
2021-12-20T14:45:57Z

From: Stefan Agner <stefan@agner.ch>

commit f9b58e8c7d031b0daa5c9a9ee27f5a4028ba53ac upstream.

While in theory multiple unwinders could be compiled in, it does
not make sense in practise. Use a choice to make the unwinder
selection mutually exclusive and mandatory.

Already before this commit it has not been possible to deselect
FRAME_POINTER. Remove the obsolete comment.

Furthermore, to produce a meaningful backtrace with FRAME_POINTER
enabled the kernel needs a specific function prologue:
mov ip, sp
stmfd sp!, {fp, ip, lr, pc}
sub fp, ip, #4

To get to the required prologue gcc uses apcs and no-sched-prolog.
This compiler options are not available on clang, and clang is not
able to generate the required prologue. Make the FRAME_POINTER
config symbol depending on !clang.

Suggested-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Stefan Agner <stefan@agner.ch>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Anders Roxell <anders.roxell@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
arch/arm/Kconfig.debug | 44 ++++++++++++++++++++++++++++----------------
lib/Kconfig.debug | 6 +++---
2 files changed, 31 insertions(+), 19 deletions(-)

--- a/arch/arm/Kconfig.debug
+++ b/arch/arm/Kconfig.debug
@@ -45,30 +45,42 @@ config DEBUG_WX

If in doubt, say "Y".

-# RMK wants arm kernels compiled with frame pointers or stack unwinding.
-# If you know what you are doing and are willing to live without stack
-# traces, you can get a slightly smaller kernel by setting this option to
-# n, but then RMK will have to kill you ;).
-config FRAME_POINTER
- bool
- depends on !THUMB2_KERNEL
- default y if !ARM_UNWIND || FUNCTION_GRAPH_TRACER
+choice
+ prompt "Choose kernel unwinder"
+ default UNWINDER_ARM if AEABI && !FUNCTION_GRAPH_TRACER
+ default UNWINDER_FRAME_POINTER if !AEABI || FUNCTION_GRAPH_TRACER
help
- If you say N here, the resulting kernel will be slightly smaller and
- faster. However, if neither FRAME_POINTER nor ARM_UNWIND are enabled,
- when a problem occurs with the kernel, the information that is
- reported is severely limited.
+ 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 ARM_UNWIND
- bool "Enable stack unwinding support (EXPERIMENTAL)"
+config UNWINDER_FRAME_POINTER
+ bool "Frame pointer unwinder"
+ depends on !THUMB2_KERNEL && !CC_IS_CLANG
+ select ARCH_WANT_FRAME_POINTERS
+ select FRAME_POINTER
+ help
+ This option enables the frame pointer unwinder for unwinding
+ kernel stack traces.
+
+config UNWINDER_ARM
+ bool "ARM EABI stack unwinder"
depends on AEABI
- default y
+ select ARM_UNWIND
help
This option enables stack unwinding support in the kernel
using the information automatically generated by the
compiler. The resulting kernel image is slightly bigger but
the performance is not affected. Currently, this feature
- only works with EABI compilers. If unsure say Y.
+ only works with EABI compilers.
+
+endchoice
+
+config ARM_UNWIND
+ bool
+
+config FRAME_POINTER
+ bool

config OLD_MCOUNT
bool
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -1178,7 +1178,7 @@ config LOCKDEP
bool
depends on DEBUG_KERNEL && LOCK_DEBUGGING_SUPPORT
select STACKTRACE
- select FRAME_POINTER if !MIPS && !PPC && !ARM_UNWIND && !S390 && !MICROBLAZE && !ARC && !X86
+ select FRAME_POINTER if !MIPS && !PPC && !ARM && !S390 && !MICROBLAZE && !ARC && !X86
select KALLSYMS
select KALLSYMS_ALL

@@ -1589,7 +1589,7 @@ 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 && !X86
+ select FRAME_POINTER if !MIPS && !PPC && !S390 && !MICROBLAZE && !ARM && !ARC && !X86
help
Provide stacktrace filter for fault-injection capabilities

@@ -1598,7 +1598,7 @@ 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 && !X86
+ select FRAME_POINTER if !MIPS && !PPC && !S390 && !MICROBLAZE && !ARM && !ARC && !X86
select KALLSYMS
select KALLSYMS_ALL
select STACKTRACE