ARM: fix function graph tracer and unwinder dependencies

Naresh Kamboju recently reported that the function-graph tracer crashes
on ARM. The function-graph tracer assumes that the kernel is built with
frame pointers.

We explicitly disabled the function-graph tracer when building Thumb2,
since the Thumb2 ABI doesn't have frame pointers.

We recently changed the way the unwinder method was selected, which
seems to have made it more likely that we can end up with the function-
graph tracer enabled but without the kernel built with frame pointers.

Fix up the function graph tracer dependencies so the option is not
available when we have no possibility of having frame pointers, and
adjust the dependencies on the unwinder option to hide the non-frame
pointer unwinder options if the function-graph tracer is enabled.

Reviewed-by: Masami Hiramatsu <mhiramat@kernel.org>
Tested-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>

2 files changed, 4 insertions, 4 deletions

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 054ead960f98..5bd8d781b9ff 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -73,7 +73,7 @@ config ARM
         select HAVE_EFFICIENT_UNALIGNED_ACCESS if (CPU_V6 || CPU_V6K || CPU_V7) && MMU
         select HAVE_EXIT_THREAD
         select HAVE_FTRACE_MCOUNT_RECORD if !XIP_KERNEL
-        select HAVE_FUNCTION_GRAPH_TRACER if !THUMB2_KERNEL
+        select HAVE_FUNCTION_GRAPH_TRACER if !THUMB2_KERNEL && !CC_IS_CLANG
         select HAVE_FUNCTION_TRACER if !XIP_KERNEL
         select HAVE_GCC_PLUGINS
         select HAVE_HW_BREAKPOINT if PERF_EVENTS && (CPU_V6 || CPU_V6K || CPU_V7)
diff --git a/arch/arm/Kconfig.debug b/arch/arm/Kconfig.debug
index 6d6e0330930b..e388af4594a6 100644
--- a/arch/arm/Kconfig.debug
+++ b/arch/arm/Kconfig.debug
@@ -47,8 +47,8 @@ config DEBUG_WX
 
 choice
         prompt "Choose kernel unwinder"
-        default UNWINDER_ARM if AEABI && !FUNCTION_GRAPH_TRACER
-        default UNWINDER_FRAME_POINTER if !AEABI || FUNCTION_GRAPH_TRACER
+        default UNWINDER_ARM if AEABI
+        default UNWINDER_FRAME_POINTER if !AEABI
         help
           This determines which method will be used for unwinding kernel stack
           traces for panics, oopses, bugs, warnings, perf, /proc/<pid>/stack,
@@ -65,7 +65,7 @@ config UNWINDER_FRAME_POINTER
 
 config UNWINDER_ARM
         bool "ARM EABI stack unwinder"
-        depends on AEABI
+        depends on AEABI && !FUNCTION_GRAPH_TRACER
         select ARM_UNWIND
         help
           This option enables stack unwinding support in the kernel