* ARM: config issue with ftrace function graph tracer
@ 2019-01-12 1:01 Jeremy Fertic
2019-01-13 15:41 ` Stefan Agner
0 siblings, 1 reply; 4+ messages in thread
From: Jeremy Fertic @ 2019-01-12 1:01 UTC (permalink / raw)
To: Stefan Agner
Cc: linux-arm-kernel, rostedt, Russell King, Arnd Bergmann, linux-kernel
I'm having a problem with the ftrace function graph tracer on a 32 bit arm
board (orangepi pc). A bisect points to the following commit:
f9b58e8c7d03 ("ARM: 8800/1: use choice for kernel unwinders")
Before this commit, if I use sunxi_defconfig and then menuconfig to enable
FTRACE and FUNCTION_TRACER then the function graph tracer works. With this
commit, and as of v5.0-rc1, doing the same as above results in a broken
function graph tracer and often an oops as well. The commit introduces a
choice group and it looks like it should default to UNWINDER_FRAME_POINTER
if FUNCTION_GRAPH_TRACER is enabled. FUNCTION_GRAPH_TRACER is enabled by
default when I enable FUNCTION_TRACER but this has no effect on the choice.
The choice always defaults to the other option which is UNWINDER_ARM. If I
manually choose UNWINDER_FRAME_POINTER then the function graph tracer works
fine.
Any idea why the default behaviour has changed?
Thanks,
Jeremy
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^ permalink raw reply [flat|nested] 4+ messages in thread* Re: ARM: config issue with ftrace function graph tracer 2019-01-12 1:01 ARM: config issue with ftrace function graph tracer Jeremy Fertic @ 2019-01-13 15:41 ` Stefan Agner 2019-01-13 16:14 ` Russell King - ARM Linux 0 siblings, 1 reply; 4+ messages in thread From: Stefan Agner @ 2019-01-13 15:41 UTC (permalink / raw) To: Jeremy Fertic Cc: linux-arm-kernel, rostedt, Russell King, Arnd Bergmann, linux-kernel Hi, On 12.01.2019 02:01, Jeremy Fertic wrote: > I'm having a problem with the ftrace function graph tracer on a 32 bit arm > board (orangepi pc). A bisect points to the following commit: > > f9b58e8c7d03 ("ARM: 8800/1: use choice for kernel unwinders") > > Before this commit, if I use sunxi_defconfig and then menuconfig to enable > FTRACE and FUNCTION_TRACER then the function graph tracer works. With this > commit, and as of v5.0-rc1, doing the same as above results in a broken > function graph tracer and often an oops as well. The commit introduces a > choice group and it looks like it should default to UNWINDER_FRAME_POINTER > if FUNCTION_GRAPH_TRACER is enabled. FUNCTION_GRAPH_TRACER is enabled by > default when I enable FUNCTION_TRACER but this has no effect on the choice. > The choice always defaults to the other option which is UNWINDER_ARM. If I > manually choose UNWINDER_FRAME_POINTER then the function graph tracer works > fine. The default selection is there, but this is made at "make sunxi_defconfig" time. At this point FUNCTION_GRAPH_TRACER is not enabled, hence Kconfig uses UNWIDER_ARM. However, when enabling the FUNCTION_GRAPH_TRACER Kconfig will _not_ reconsider and switch enable UNWINDER_FRAME_POINTER. Before that commit, when enabling FUNCTION_GRAPH_TRACER, we simply also enabled FRAME_POINTER... I guess we need to make sure that FUNCTION_GRAPH_TRACER depends on the UNWINDER_FRAME_POINTER choice. There is already a similar dependency with THUMB2_KERNEL. We can cleanup that dependency since UNWINDER_FRAME_POINTER already depends on !THUMB2_KERNEL. diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig index 664e918e2624..a2ac65a8b2cc 100644 --- a/arch/arm/Kconfig +++ b/arch/arm/Kconfig @@ -69,7 +69,7 @@ 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 UNWINDER_FRAME_POINTER select HAVE_FUNCTION_TRACER if !XIP_KERNEL select HAVE_GCC_PLUGINS select HAVE_GENERIC_DMA_COHERENT diff --git a/arch/arm/Kconfig.debug b/arch/arm/Kconfig.debug index 6d6e0330930b..8341649fa71d 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, > > Any idea why the default behaviour has changed? The rational is stated in the commit message, the main reason was to disallow UNWINDER_FRAME_POINTER in case Clang is used (since Clang does not create the expected function prologue). The choice also aligns with how unwinders are selected on x86. -- Stefan _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel ^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: ARM: config issue with ftrace function graph tracer 2019-01-13 15:41 ` Stefan Agner @ 2019-01-13 16:14 ` Russell King - ARM Linux 2019-01-15 22:37 ` Stefan Agner 0 siblings, 1 reply; 4+ messages in thread From: Russell King - ARM Linux @ 2019-01-13 16:14 UTC (permalink / raw) To: Stefan Agner Cc: linux-arm-kernel, Jeremy Fertic, rostedt, Arnd Bergmann, linux-kernel On Sun, Jan 13, 2019 at 04:41:52PM +0100, Stefan Agner wrote: > Hi, > > On 12.01.2019 02:01, Jeremy Fertic wrote: > > I'm having a problem with the ftrace function graph tracer on a 32 bit arm > > board (orangepi pc). A bisect points to the following commit: > > > > f9b58e8c7d03 ("ARM: 8800/1: use choice for kernel unwinders") > > > > Before this commit, if I use sunxi_defconfig and then menuconfig to enable > > FTRACE and FUNCTION_TRACER then the function graph tracer works. With this > > commit, and as of v5.0-rc1, doing the same as above results in a broken > > function graph tracer and often an oops as well. The commit introduces a > > choice group and it looks like it should default to UNWINDER_FRAME_POINTER > > if FUNCTION_GRAPH_TRACER is enabled. FUNCTION_GRAPH_TRACER is enabled by > > default when I enable FUNCTION_TRACER but this has no effect on the choice. > > The choice always defaults to the other option which is UNWINDER_ARM. If I > > manually choose UNWINDER_FRAME_POINTER then the function graph tracer works > > fine. > > The default selection is there, but this is made at "make > sunxi_defconfig" time. At this point FUNCTION_GRAPH_TRACER is not > enabled, hence Kconfig uses UNWIDER_ARM. However, when enabling the > FUNCTION_GRAPH_TRACER Kconfig will _not_ reconsider and switch enable > UNWINDER_FRAME_POINTER. > > Before that commit, when enabling FUNCTION_GRAPH_TRACER, we simply also > enabled FRAME_POINTER... > > I guess we need to make sure that FUNCTION_GRAPH_TRACER depends on the > UNWINDER_FRAME_POINTER choice. There is already a similar dependency > with THUMB2_KERNEL. We can cleanup that dependency since > UNWINDER_FRAME_POINTER already depends on !THUMB2_KERNEL. > > diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig > index 664e918e2624..a2ac65a8b2cc 100644 > --- a/arch/arm/Kconfig > +++ b/arch/arm/Kconfig > @@ -69,7 +69,7 @@ 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 UNWINDER_FRAME_POINTER > select HAVE_FUNCTION_TRACER if !XIP_KERNEL > select HAVE_GCC_PLUGINS > select HAVE_GENERIC_DMA_COHERENT > diff --git a/arch/arm/Kconfig.debug b/arch/arm/Kconfig.debug > index 6d6e0330930b..8341649fa71d 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, This looks rather horrid - the upshot of this means that the function tracer becomes unavailable on EABI unless you know that you must change the unwinder from its default. Before the change to the choice statement, people could select the function graph tracer, and the correct unwinder would be selected for them. That's knowledge that people never required before, and I think it's really quite unfair to require them to know this to use the function graph tracer. Maybe someone can put some effort into getting the function graph tracer working with non-framepointer kernels... but as the above currently stands, I really don't like the patch and I'd much rather revert the original change to fix this regression. -- RMK's Patch system: http://www.armlinux.org.uk/developer/patches/ FTTC broadband for 0.8mile line in suburbia: sync at 12.1Mbps down 622kbps up According to speedtest.net: 11.9Mbps down 500kbps up _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel ^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: ARM: config issue with ftrace function graph tracer 2019-01-13 16:14 ` Russell King - ARM Linux @ 2019-01-15 22:37 ` Stefan Agner 0 siblings, 0 replies; 4+ messages in thread From: Stefan Agner @ 2019-01-15 22:37 UTC (permalink / raw) To: Stefan Agner Cc: Arnd Bergmann, Jeremy Fertic, Russell King - ARM Linux, rostedt, linux-kernel, linux-arm-kernel On 13.01.2019 17:14, Russell King - ARM Linux wrote: > On Sun, Jan 13, 2019 at 04:41:52PM +0100, Stefan Agner wrote: >> Hi, >> >> On 12.01.2019 02:01, Jeremy Fertic wrote: >> > I'm having a problem with the ftrace function graph tracer on a 32 bit arm >> > board (orangepi pc). A bisect points to the following commit: >> > >> > f9b58e8c7d03 ("ARM: 8800/1: use choice for kernel unwinders") >> > >> > Before this commit, if I use sunxi_defconfig and then menuconfig to enable >> > FTRACE and FUNCTION_TRACER then the function graph tracer works. With this >> > commit, and as of v5.0-rc1, doing the same as above results in a broken >> > function graph tracer and often an oops as well. The commit introduces a >> > choice group and it looks like it should default to UNWINDER_FRAME_POINTER >> > if FUNCTION_GRAPH_TRACER is enabled. FUNCTION_GRAPH_TRACER is enabled by >> > default when I enable FUNCTION_TRACER but this has no effect on the choice. >> > The choice always defaults to the other option which is UNWINDER_ARM. If I >> > manually choose UNWINDER_FRAME_POINTER then the function graph tracer works >> > fine. >> >> The default selection is there, but this is made at "make >> sunxi_defconfig" time. At this point FUNCTION_GRAPH_TRACER is not >> enabled, hence Kconfig uses UNWIDER_ARM. However, when enabling the >> FUNCTION_GRAPH_TRACER Kconfig will _not_ reconsider and switch enable >> UNWINDER_FRAME_POINTER. >> >> Before that commit, when enabling FUNCTION_GRAPH_TRACER, we simply also >> enabled FRAME_POINTER... >> >> I guess we need to make sure that FUNCTION_GRAPH_TRACER depends on the >> UNWINDER_FRAME_POINTER choice. There is already a similar dependency >> with THUMB2_KERNEL. We can cleanup that dependency since >> UNWINDER_FRAME_POINTER already depends on !THUMB2_KERNEL. >> >> diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig >> index 664e918e2624..a2ac65a8b2cc 100644 >> --- a/arch/arm/Kconfig >> +++ b/arch/arm/Kconfig >> @@ -69,7 +69,7 @@ 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 UNWINDER_FRAME_POINTER >> select HAVE_FUNCTION_TRACER if !XIP_KERNEL >> select HAVE_GCC_PLUGINS >> select HAVE_GENERIC_DMA_COHERENT >> diff --git a/arch/arm/Kconfig.debug b/arch/arm/Kconfig.debug >> index 6d6e0330930b..8341649fa71d 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, > > This looks rather horrid - the upshot of this means that the function > tracer becomes unavailable on EABI unless you know that you must change > the unwinder from its default. > > Before the change to the choice statement, people could select the > function graph tracer, and the correct unwinder would be selected > for them. That's knowledge that people never required before, and > I think it's really quite unfair to require them to know this to use > the function graph tracer. It is not ideal I agree. Searching for the symbol FUNCTION_GRAPH_TRACER in menuconfig immediately shows what dependency are missing. Also, we used to have the same situation with THUMB2_KERNEL already: You had to know that you need to disable Thumb2 Kernel in order to see FUNCTION_GRAPH_TRACER. > > Maybe someone can put some effort into getting the function graph > tracer working with non-framepointer kernels... but as the above > currently stands, I really don't like the patch and I'd much rather > revert the original change to fix this regression. I am all for that effort. Using Thumb2 on Arm32 is also getting more popular. Is known what is exactly missing/what effort would be required? -- Stefan _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel ^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2019-01-15 22:38 UTC | newest] Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2019-01-12 1:01 ARM: config issue with ftrace function graph tracer Jeremy Fertic 2019-01-13 15:41 ` Stefan Agner 2019-01-13 16:14 ` Russell King - ARM Linux 2019-01-15 22:37 ` Stefan Agner
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