[PATCH v2] powerpc/64: BE option to use ELFv2 ABI for big endian kernels

Nicholas Piggin npiggin at gmail.com
Tue May 4 19:13:39 AEST 2021


Excerpts from Michal Suchánek's message of May 4, 2021 6:17 am:
> On Mon, May 03, 2021 at 11:34:25AM +0200, Michal Suchánek wrote:
>> On Mon, May 03, 2021 at 09:11:16AM +0200, Michal Suchánek wrote:
>> > On Mon, May 03, 2021 at 10:58:33AM +1000, Nicholas Piggin wrote:
>> > > Excerpts from Michal Suchánek's message of May 3, 2021 2:57 am:
>> > > > On Tue, Apr 28, 2020 at 09:25:17PM +1000, Nicholas Piggin wrote:
>> > > >> Provide an option to use ELFv2 ABI for big endian builds. This works on
>> > > >> GCC and clang (since 2014). It is less well tested and supported by the
>> > > >> GNU toolchain, but it can give some useful advantages of the ELFv2 ABI
>> > > >> for BE (e.g., less stack usage). Some distros even build BE ELFv2
>> > > >> userspace.
>> > > > 
>> > > > Fixes BTFID failure on BE for me and the ELF ABIv2 kernel boots.
>> > > 
>> > > What's the BTFID failure? Anything we can do to fix it on the v1 ABI or 
>> > > at least make it depend on BUILD_ELF_V2?
>> > 
>> > Looks like symbols are prefixed with a dot in ABIv1 and BTFID tool is
>> > not aware of that. It can be disabled on ABIv1 easily.
>> > 
>> > Thanks
>> > 
>> > Michal
>> > 
>> > diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
>> > index 678c13967580..e703c26e9b80 100644
>> > --- a/lib/Kconfig.debug
>> > +++ b/lib/Kconfig.debug
>> > @@ -305,6 +305,7 @@ config DEBUG_INFO_BTF
>> >  	bool "Generate BTF typeinfo"
>> >  	depends on !DEBUG_INFO_SPLIT && !DEBUG_INFO_REDUCED
>> >  	depends on !GCC_PLUGIN_RANDSTRUCT || COMPILE_TEST
>> > +	depends on !PPC64 || BUILD_ELF_V2
>> >  	help
>> >  	  Generate deduplicated BTF type information from DWARF debug info.
>> >  	  Turning this on expects presence of pahole tool, which will convert
>> > 
>> > > 
>> > > > 
>> > > > Tested-by: Michal Suchánek <msuchanek at suse.de>
>> > > > 
>> > > > Also can we enable mprofile on BE now?
>> > > > 
>> > > > I don't see anything endian-specific in the mprofile code at a glance
>> > > > but don't have any idea how to test it.
>> > > 
>> > > AFAIK it's just a different ABI for the _mcount call so just running
>> > > some ftrace and ftrace with call graph should test it reasonably well.
>> 
>> It does not crash and burn but there are some regressions from LE to BE
>> on the ftrace kernel selftest:
>> 
>> --- ftraceLE.txt	2021-05-03 11:19:14.830000000 +0200
>> +++ ftraceBE.txt	2021-05-03 11:27:24.770000000 +0200
>> @@ -7,8 +7,8 @@
>>  [n] Change the ringbuffer size	[PASS]
>>  [n] Snapshot and tracing setting	[PASS]
>>  [n] trace_pipe and trace_marker	[PASS]
>> -[n] Test ftrace direct functions against tracers	[UNRESOLVED]
>> -[n] Test ftrace direct functions against kprobes	[UNRESOLVED]
>> +[n] Test ftrace direct functions against tracers	[FAIL]
>> +[n] Test ftrace direct functions against kprobes	[FAIL]
>>  [n] Generic dynamic event - add/remove kprobe events	[PASS]
>>  [n] Generic dynamic event - add/remove synthetic events	[PASS]
>>  [n] Generic dynamic event - selective clear (compatibility)	[PASS]
>> @@ -16,10 +16,10 @@
>>  [n] event tracing - enable/disable with event level files	[PASS]
>>  [n] event tracing - restricts events based on pid notrace filtering	[PASS]
>>  [n] event tracing - restricts events based on pid	[PASS]
>> -[n] event tracing - enable/disable with subsystem level files	[PASS]
>> +[n] event tracing - enable/disable with subsystem level files	[FAIL]
>>  [n] event tracing - enable/disable with top level files	[PASS]
>> -[n] Test trace_printk from module	[UNRESOLVED]
>> -[n] ftrace - function graph filters with stack tracer	[PASS]
>> +[n] Test trace_printk from module	[FAIL]
>> +[n] ftrace - function graph filters with stack tracer	[FAIL]
>>  [n] ftrace - function graph filters	[PASS]
>>  [n] ftrace - function trace with cpumask	[PASS]
>>  [n] ftrace - test for function event triggers	[PASS]
>> @@ -27,7 +27,7 @@
>>  [n] ftrace - function pid notrace filters	[PASS]
>>  [n] ftrace - function pid filters	[PASS]
>>  [n] ftrace - stacktrace filter command	[PASS]
>> -[n] ftrace - function trace on module	[UNRESOLVED]
>> +[n] ftrace - function trace on module	[FAIL]
>>  [n] ftrace - function profiler with function tracing	[PASS]
>>  [n] ftrace - function profiling	[PASS]
>>  [n] ftrace - test reading of set_ftrace_filter	[PASS]
>> @@ -44,10 +44,10 @@
>>  [n] Kprobe event argument syntax	[PASS]
>>  [n] Kprobe dynamic event with arguments	[PASS]
>>  [n] Kprobes event arguments with types	[PASS]
>> -[n] Kprobe event user-memory access	[UNSUPPORTED]
>> +[n] Kprobe event user-memory access	[FAIL]
>>  [n] Kprobe event auto/manual naming	[PASS]
>>  [n] Kprobe dynamic event with function tracer	[PASS]
>> -[n] Kprobe dynamic event - probing module	[UNRESOLVED]
>> +[n] Kprobe dynamic event - probing module	[FAIL]
>>  [n] Create/delete multiprobe on kprobe event	[PASS]
>>  [n] Kprobe event parser error log check	[PASS]
>>  [n] Kretprobe dynamic event with arguments	[PASS]
>> @@ -57,11 +57,11 @@
>>  [n] Kprobe events - probe points	[PASS]
>>  [n] Kprobe dynamic event - adding and removing	[PASS]
>>  [n] Uprobe event parser error log check	[PASS]
>> -[n] test for the preemptirqsoff tracer	[UNSUPPORTED]
>> -[n] Meta-selftest: Checkbashisms	[UNRESOLVED]
>> +[n] test for the preemptirqsoff tracer	[FAIL]
>> +[n] Meta-selftest: Checkbashisms	[FAIL]
>>  [n] Test wakeup RT tracer	[PASS]
>>  [n] Test wakeup tracer	[PASS]
>> -[n] event trigger - test inter-event histogram trigger expected fail actions	[XFAIL]
>> +[n] event trigger - test inter-event histogram trigger expected fail actions	[FAIL]
>>  [n] event trigger - test field variable support	[PASS]
>>  [n] event trigger - test inter-event combined histogram trigger	[PASS]
>>  [n] event trigger - test multiple actions on hist trigger	[PASS]
>> @@ -96,7 +96,8 @@
>>  [n] (instance)  event tracing - enable/disable with event level files	[PASS]
>>  [n] (instance)  event tracing - restricts events based on pid notrace filtering	[PASS]
>>  [n] (instance)  event tracing - restricts events based on pid	[PASS]
>> -[n] (instance)  event tracing - enable/disable with subsystem level files	[PASS]
>> +[n] (instance)  event tracing - enable/disable with subsystem level files	[FAIL]
>> +rmdir: failed to remove '/sys/kernel/tracing/instances/ftracetest.mceByV': Device or resource busy
>>  [n] (instance)  ftrace - test for function event triggers	[PASS]
>>  [n] (instance)  ftrace - function pid notrace filters	[PASS]
>>  [n] (instance)  ftrace - function pid filters	[PASS]
>> 
>> I needed to add a test timeout to get this far because
>> "event tracing - enable/disable with subsystem level files" gets stuck.
> 
> There is some regression from mprofile on BE ABIv2
> 
> --- ftraceBEv2.txt	2021-05-03 18:11:01.100000000 +0200
> +++ ftraceBE.mprofile.txt	2021-05-03 11:27:24.770000000 +0200
> @@ -19,7 +19,7 @@
>  [n] event tracing - enable/disable with subsystem level files	[FAIL]
>  [n] event tracing - enable/disable with top level files	[PASS]
>  [n] Test trace_printk from module	[FAIL]
> -[n] ftrace - function graph filters with stack tracer	[PASS]
> +[n] ftrace - function graph filters with stack tracer	[FAIL]
>  [n] ftrace - function graph filters	[PASS]
>  [n] ftrace - function trace with cpumask	[PASS]
>  [n] ftrace - test for function event triggers	[PASS]
> @@ -31,7 +31,7 @@
>  [n] ftrace - function profiler with function tracing	[PASS]
>  [n] ftrace - function profiling	[PASS]
>  [n] ftrace - test reading of set_ftrace_filter	[PASS]
> -[n] ftrace - Max stack tracer	[PASS]
> +[n] ftrace - Max stack tracer	[FAIL]
>  [n] ftrace - test for function traceon/off triggers	[PASS]
>  [n] ftrace - test tracing error log support	[PASS]
>  [n] Test creation and deletion of trace instances while setting an event	[PASS]

Hmm, I don't see an obvious case where the stack layout is based on
BE when it should be using ELF ABI version, or ftrace_64_mprofile.S
depends on LE. +Naveen

> 
> but generally the ftrace on BE is broken overall. The test
> "event tracing - enable/disable with subsystem level files" gets stuck
> and has to be killed by timeout. Running the testsuite twice the test
> "Basic test for tracers" locks up the machine regardless of using
> mprofile. The ABIV1 is even much worse with the exception of
> "(instance)  event tracing - enable/disable with subsystem level files"
> which regresses on BE ABIv2 in general.

Wow it has fixed quite a few! That event tracing one hardly looks like
a difficult test, hopefully should be something trivial.

Thanks for testing.

Thanks,
Nick

> 
> --- ftraceBEv1.txt	2021-05-03 22:09:10.690000000 +0200
> +++ ftraceBEv2.txt	2021-05-03 18:11:01.100000000 +0200
> @@ -9,10 +9,10 @@
>  [n] trace_pipe and trace_marker	[PASS]
>  [n] Test ftrace direct functions against tracers	[FAIL]
>  [n] Test ftrace direct functions against kprobes	[FAIL]
> -[n] Generic dynamic event - add/remove kprobe events	[FAIL]
> +[n] Generic dynamic event - add/remove kprobe events	[PASS]
>  [n] Generic dynamic event - add/remove synthetic events	[PASS]
> -[n] Generic dynamic event - selective clear (compatibility)	[FAIL]
> -[n] Generic dynamic event - generic clear event	[FAIL]
> +[n] Generic dynamic event - selective clear (compatibility)	[PASS]
> +[n] Generic dynamic event - generic clear event	[PASS]
>  [n] event tracing - enable/disable with event level files	[PASS]
>  [n] event tracing - restricts events based on pid notrace filtering	[PASS]
>  [n] event tracing - restricts events based on pid	[PASS]
> @@ -23,39 +23,39 @@
>  [n] ftrace - function graph filters	[PASS]
>  [n] ftrace - function trace with cpumask	[PASS]
>  [n] ftrace - test for function event triggers	[PASS]
> -[n] ftrace - function glob filters	[FAIL]
> +[n] ftrace - function glob filters	[PASS]
>  [n] ftrace - function pid notrace filters	[PASS]
>  [n] ftrace - function pid filters	[PASS]
>  [n] ftrace - stacktrace filter command	[PASS]
>  [n] ftrace - function trace on module	[FAIL]
>  [n] ftrace - function profiler with function tracing	[PASS]
>  [n] ftrace - function profiling	[PASS]
> -[n] ftrace - test reading of set_ftrace_filter	[FAIL]
> +[n] ftrace - test reading of set_ftrace_filter	[PASS]
>  [n] ftrace - Max stack tracer	[PASS]
>  [n] ftrace - test for function traceon/off triggers	[PASS]
>  [n] ftrace - test tracing error log support	[PASS]
>  [n] Test creation and deletion of trace instances while setting an event	[PASS]
>  [n] Test creation and deletion of trace instances	[PASS]
> -[n] Kprobe dynamic event - adding and removing	[FAIL]
> -[n] Kprobe dynamic event - busy event check	[FAIL]
> -[n] Kprobe dynamic event with arguments	[FAIL]
> -[n] Kprobe event with comm arguments	[FAIL]
> -[n] Kprobe event string type argument	[FAIL]
> -[n] Kprobe event symbol argument	[FAIL]
> -[n] Kprobe event argument syntax	[FAIL]
> -[n] Kprobes event arguments with types	[FAIL]
> +[n] Kprobe dynamic event - adding and removing	[PASS]
> +[n] Kprobe dynamic event - busy event check	[PASS]
> +[n] Kprobe event with comm arguments	[PASS]
> +[n] Kprobe event string type argument	[PASS]
> +[n] Kprobe event symbol argument	[PASS]
> +[n] Kprobe event argument syntax	[PASS]
> +[n] Kprobe dynamic event with arguments	[PASS]
> +[n] Kprobes event arguments with types	[PASS]
>  [n] Kprobe event user-memory access	[FAIL]
>  [n] Kprobe event auto/manual naming	[PASS]
> -[n] Kprobe dynamic event with function tracer	[FAIL]
> +[n] Kprobe dynamic event with function tracer	[PASS]
>  [n] Kprobe dynamic event - probing module	[FAIL]
> -[n] Create/delete multiprobe on kprobe event	[FAIL]
> -[n] Kprobe event parser error log check	[FAIL]
> -[n] Kretprobe dynamic event with arguments	[FAIL]
> -[n] Kretprobe dynamic event with maxactive	[FAIL]
> -[n] Kretprobe %return suffix test	[FAIL]
> -[n] Register/unregister many kprobe events	[FAIL]
> -[n] Kprobe events - probe points	[FAIL]
> -[n] Kprobe dynamic event - adding and removing	[FAIL]
> +[n] Create/delete multiprobe on kprobe event	[PASS]
> +[n] Kprobe event parser error log check	[PASS]
> +[n] Kretprobe dynamic event with arguments	[PASS]
> +[n] Kretprobe dynamic event with maxactive	[PASS]
> +[n] Kretprobe %return suffix test	[PASS]
> +[n] Register/unregister many kprobe events	[PASS]
> +[n] Kprobe events - probe points	[PASS]
> +[n] Kprobe dynamic event - adding and removing	[PASS]
>  [n] Uprobe event parser error log check	[PASS]
>  [n] test for the preemptirqsoff tracer	[FAIL]
>  [n] Meta-selftest: Checkbashisms	[FAIL]
> @@ -96,7 +96,8 @@
>  [n] (instance)  event tracing - enable/disable with event level files	[PASS]
>  [n] (instance)  event tracing - restricts events based on pid notrace filtering	[PASS]
>  [n] (instance)  event tracing - restricts events based on pid	[PASS]
> -[n] (instance)  event tracing - enable/disable with subsystem level files	[PASS]
> +[n] (instance)  event tracing - enable/disable with subsystem level files	[FAIL]
> +rmdir: failed to remove '/sys/kernel/tracing/instances/ftracetest.lxCI5k': Device or resource busy
>  [n] (instance)  ftrace - test for function event triggers	[PASS]
>  [n] (instance)  ftrace - function pid notrace filters	[PASS]
>  [n] (instance)  ftrace - function pid filters	[PASS]
> 
> 
> Thanks
> 
> Michal
> 


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