Messages in this thread | | | Date | Tue, 23 Apr 2019 22:37:11 +0200 | From | Stefan Agner <> | Subject | Re: Kconfig dependency issue on function-graph tracer and frame pointer on arm |
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On 15.04.2019 14:28, Arnd Bergmann wrote: > On Sun, Apr 14, 2019 at 3:35 PM Russell King - ARM Linux admin > <linux@armlinux.org.uk> wrote: > >> The subsequent hunks remove the defaulting of the choice according to >> the function graph tracer - this is not a "hint" where the user can >> still choose either option irrespective of the state of the function >> graph tracer. They should only be able to select the frame pointer >> option in that case. >> >> Another way forward would be for someone to put the work in to making >> the function graph tracer work without frame pointers. > > I think Stefan was already looking into making CONFIG_FUNCTION_TRACER > work with clang. I don't know what the status of that work is, but I > think getting > FUNCTION_GRAPH_TRACER working at the same time would be best.
Function Tracer is currently blocked by buggy mcount implemention on Clang side. I do have a hacked up version which works with the buggy Clang implementation, but not something we want to merge IMHO. see also: https://bugs.llvm.org/show_bug.cgi?id=33845
> > I never noticed the Kconfig issue here, because I was using a patch to > turn off FUNCTION_TRACER on ARM with clang to make it build, and that > turns off FUNCTION_GRAPH_TRACER in the process. > >> So, how about this: >> >> diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig >> index 850b4805e2d1..9aed25a6019b 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
I think due to the fact above, we should add && !CC_IS_CLANG here too.
>> 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 > > This looks good to me in the meantime, at least if there is any > way to get the non-graph FUNCTION_TRACER to build with clang.
Looks sensible to me too.
Note that a similar issue came up a while ago on the mailing list: https://marc.info/?l=linux-arm-kernel&m=154739414703313&w=2 [added Jeremy]
Unfortunately this never really materialized in a mergeable patch.
-- Stefan
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