ARM: 8800/1: use choice for kernel unwinders

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>

diff --git a/arch/arm/Kconfig.debug b/arch/arm/Kconfig.debug
index c155b11e2e872f47408704d0ae746e625ea1dde3..a810fa8ba4041f3d6333aef30c28c2c32c00ec5d 100644 (file)
--- 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
+         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 UNWINDER_FRAME_POINTER
+       bool "Frame pointer unwinder"
+       depends on !THUMB2_KERNEL && !CC_IS_CLANG
+       select ARCH_WANT_FRAME_POINTERS
+       select FRAME_POINTER
        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 option enables the frame pointer unwinder for unwinding
+         kernel stack traces.
 
-config ARM_UNWIND
-       bool "Enable stack unwinding support (EXPERIMENTAL)"
+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 DEBUG_USER
        bool "Verbose user fault messages"

diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 613316724c6af63ea9f93fccffb6b6010cdde82e..25188b322326a7bdfd12d88af281a806384de7db 100644 (file)
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -1179,7 +1179,7 @@ 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
 
@@ -1590,7 +1590,7 @@ 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
 
@@ -1599,7 +1599,7 @@ 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