Danilo Cezar Zanella reported broken function graph tracer in the v4.19 tree. This was caused by the backport of commit f9b58e8c7d031 ("ARM: 8800/1: use choice for kernel unwinders")

which ended in the v4.19-stable tree as of v4.19.222. It is also part of v4.14-stable since v4.14.259. It is also part of v4.9-stable since v4.9.299.

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From: Russell King rmk+kernel@armlinux.org.uk Date: Tue, 23 Apr 2019 17:09:38 +0100 Subject: [PATCH] ARM: fix function graph tracer and unwinder dependencies

Upstream commit 503621628b32782a07b2318e4112bd4372aa3401

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 Signed-off-by: Sebastian Andrzej Siewior bigeasy@linutronix.de Reported-by: Danilo Cezar Zanella danilo.zanella@iag.usp.br --- arch/arm/Kconfig | 2 +- arch/arm/Kconfig.debug | 6 +++--- 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig index d89d013f586cb..fce7e85f3ef57 100644 --- a/arch/arm/Kconfig +++ b/arch/arm/Kconfig @@ -68,7 +68,7 @@ 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_FUTEX_CMPXCHG if FUTEX select HAVE_GCC_PLUGINS diff --git a/arch/arm/Kconfig.debug b/arch/arm/Kconfig.debug index 01c760929c9e4..b931fac129a1b 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