Message-ID: <03a8fcbe-4f35-757a-b3f6-b3fdaa22966c@foss.arm.com>
Date:   Tue, 4 Jan 2022 15:15:27 +0000
From:   Carsten Haitzler <carsten.haitzler@...s.arm.com>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Leo Yan <leo.yan@...aro.org>
Cc:     linux-kernel@...r.kernel.org, coresight@...ts.linaro.org,
        suzuki.poulose@....com, mathieu.poirier@...aro.org,
        mike.leach@...aro.org, inux-perf-users@...r.kernel.org
Subject: Re: [PATCH 04/12] perf test: Add beginning of test infra + test to
 exercise coresight



On 12/21/21 20:40, Arnaldo Carvalho de Melo wrote:
> Em Tue, Dec 21, 2021 at 11:03:49PM +0800, Leo Yan escreveu:
>> Hi Carsten,
>>
>> On Wed, Dec 15, 2021 at 04:03:55PM +0000, carsten.haitzler@...s.arm.com wrote:
>>> From: Carsten Haitzler <carsten.haitzler@....com>
>>>
>>> This adds the initial test harness to run perf record and examine the
>>> resuling output when coresight is enabled on arm64 and check the
>>> resulting quality of the output as part of perf test.
>>>
>>> Signed-off-by: Carsten Haitzler <carsten.haitzler@....com>
>>> ---
>>>   MAINTAINERS                                   |   3 +
>>>   tools/perf/Makefile.perf                      |  14 +-
>>>   .../tests/shell/coresight_asm_pure_loop.sh    |  18 +++
>>>   tools/perf/tests/shell/lib/coresight.sh       | 130 ++++++++++++++++++
>>>   tools/perf/tests/shell/tools/Makefile         |  26 ++++
>>>   .../perf/tests/shell/tools/coresight/Makefile |  27 ++++
>>>   .../shell/tools/coresight/Makefile.miniconfig |  23 ++++
>>>   .../tools/coresight/asm_pure_loop/Makefile    |  30 ++++
>>>   .../coresight/asm_pure_loop/asm_pure_loop.S   |  28 ++++
>>>   9 files changed, 297 insertions(+), 2 deletions(-)
>>>   create mode 100755 tools/perf/tests/shell/coresight_asm_pure_loop.sh
>>>   create mode 100644 tools/perf/tests/shell/lib/coresight.sh
>>>   create mode 100644 tools/perf/tests/shell/tools/Makefile
>>>   create mode 100644 tools/perf/tests/shell/tools/coresight/Makefile
>>>   create mode 100644 tools/perf/tests/shell/tools/coresight/Makefile.miniconfig
>>>   create mode 100644 tools/perf/tests/shell/tools/coresight/asm_pure_loop/Makefile
>>>   create mode 100644 tools/perf/tests/shell/tools/coresight/asm_pure_loop/asm_pure_loop.S
>>
>> The folder naming is okay for me, but it is cyclic with the format:
>> "tools/.../tools/".  So I am wandering if below two pathes are better?
>>
>>    tools/perf/tests/shell/prog/coresight/
>>    or
>>    tools/perf/tests/shell/coresight/
> 
> The later, its descriptive enough, I think, and the shortest variant so
> far.

Sure - no problem. I can change that. Once no one has any more comments 
and a few of the pending thnigs I've marked to resolve are solved, I'll 
submit a new patch set.

> - Arnaldo
>   
>> I'd like to leave this question for Arnaldo / Jiri for the folder
>> layout.
>>
>>> diff --git a/MAINTAINERS b/MAINTAINERS
>>> index 13f9a84a617e..d46e8469c467 100644
>>> --- a/MAINTAINERS
>>> +++ b/MAINTAINERS
>>> @@ -1894,6 +1894,9 @@ F:	tools/perf/arch/arm/util/auxtrace.c
>>>   F:	tools/perf/arch/arm/util/cs-etm.c
>>>   F:	tools/perf/arch/arm/util/cs-etm.h
>>>   F:	tools/perf/arch/arm/util/pmu.c
>>> +F:	tools/perf/tests/shell/coresight_*
>>> +F:	tools/perf/tests/shell/tools/Makefile
>>> +F:	tools/perf/tests/shell/tools/coresight/*
>>>   F:	tools/perf/util/cs-etm-decoder/*
>>>   F:	tools/perf/util/cs-etm.*
>>>   
>>> diff --git a/tools/perf/Makefile.perf b/tools/perf/Makefile.perf
>>> index 80522bcfafe0..26467a2c71f4 100644
>>> --- a/tools/perf/Makefile.perf
>>> +++ b/tools/perf/Makefile.perf
>>> @@ -630,7 +630,15 @@ sync_file_range_tbls := $(srctree)/tools/perf/trace/beauty/sync_file_range.sh
>>>   $(sync_file_range_arrays): $(linux_uapi_dir)/fs.h $(sync_file_range_tbls)
>>>   	$(Q)$(SHELL) '$(sync_file_range_tbls)' $(linux_uapi_dir) > $@
>>>   
>>> -all: shell_compatibility_test $(ALL_PROGRAMS) $(LANG_BINDINGS) $(OTHER_PROGRAMS)
>>> +TESTS_TOOLS_DIR := $(srctree)/tools/perf/tests/shell/tools
>>> +
>>> +tests-tools-targets: FORCE
>>> +	$(Q)$(MAKE) -C $(TESTS_TOOLS_DIR)
>>> +
>>> +tests-tools-targets-clean:
>>> +	$(Q)$(MAKE) -C $(TESTS_TOOLS_DIR) clean
>>> +
>>> +all: shell_compatibility_test $(ALL_PROGRAMS) $(LANG_BINDINGS) $(OTHER_PROGRAMS) tests-tools-targets
>>>   
>>>   # Create python binding output directory if not already present
>>>   _dummy := $(shell [ -d '$(OUTPUT)python' ] || mkdir -p '$(OUTPUT)python')
>>> @@ -1020,6 +1028,7 @@ install-tests: all install-gtk
>>>   		$(INSTALL) tests/shell/*.sh '$(DESTDIR_SQ)$(perfexec_instdir_SQ)/tests/shell'; \
>>>   		$(INSTALL) -d -m 755 '$(DESTDIR_SQ)$(perfexec_instdir_SQ)/tests/shell/lib'; \
>>>   		$(INSTALL) tests/shell/lib/*.sh '$(DESTDIR_SQ)$(perfexec_instdir_SQ)/tests/shell/lib'
>>> +	$(Q)$(MAKE) -C tests/shell/tools install-tests
>>>   
>>>   install-bin: install-tools install-tests install-traceevent-plugins
>>>   
>>> @@ -1088,7 +1097,7 @@ endif # BUILD_BPF_SKEL
>>>   bpf-skel-clean:
>>>   	$(call QUIET_CLEAN, bpf-skel) $(RM) -r $(SKEL_TMP_OUT) $(SKELETONS)
>>>   
>>> -clean:: $(LIBTRACEEVENT)-clean $(LIBAPI)-clean $(LIBBPF)-clean $(LIBSUBCMD)-clean $(LIBPERF)-clean fixdep-clean python-clean bpf-skel-clean
>>> +clean:: $(LIBTRACEEVENT)-clean $(LIBAPI)-clean $(LIBBPF)-clean $(LIBSUBCMD)-clean $(LIBPERF)-clean fixdep-clean python-clean bpf-skel-clean tests-tools-targets-clean
>>>   	$(call QUIET_CLEAN, core-objs)  $(RM) $(LIBPERF_A) $(OUTPUT)perf-archive $(OUTPUT)perf-with-kcore $(OUTPUT)perf-iostat $(LANG_BINDINGS)
>>>   	$(Q)find $(if $(OUTPUT),$(OUTPUT),.) -name '*.o' -delete -o -name '\.*.cmd' -delete -o -name '\.*.d' -delete
>>>   	$(Q)$(RM) $(OUTPUT).config-detected
>>> @@ -1155,5 +1164,6 @@ FORCE:
>>>   .PHONY: shell_compatibility_test please_set_SHELL_PATH_to_a_more_modern_shell
>>>   .PHONY: $(GIT-HEAD-PHONY) TAGS tags cscope FORCE prepare
>>>   .PHONY: libtraceevent_plugins archheaders
>>> +.PHONY: $(TESTS_TOOLS_TARGETS)
>>>   
>>>   endif # force_fixdep
>>> diff --git a/tools/perf/tests/shell/coresight_asm_pure_loop.sh b/tools/perf/tests/shell/coresight_asm_pure_loop.sh
>>> new file mode 100755
>>> index 000000000000..542d4a37e349
>>> --- /dev/null
>>> +++ b/tools/perf/tests/shell/coresight_asm_pure_loop.sh
>>> @@ -0,0 +1,18 @@
>>> +#!/bin/sh -e
>>> +# Coresight / ASM Pure Loop
>>> +
>>> +# SPDX-License-Identifier: GPL-2.0
>>> +# Carsten Haitzler <carsten.haitzler@....com>, 2021
>>> +
>>> +TEST="asm_pure_loop"
>>> +. $(dirname $0)/lib/coresight.sh
>>> +ARGS=""
>>> +DATV="out"
>>> +DATA="$DATD/perf-$TEST-$DATV.data"
>>> +
>>> +perf record $PERFRECOPT -o "$DATA" "$BIN" $ARGS
>>
>> Is $ARGS redundant and can be removed?
>>
>>> +perf_dump_aux_verify "$DATA" 2601 334 334
>>
>> These three magic numbers "2601 334 334" would be hard to understand.
>> One way is the code can dynamically calculate these values based on the
>> loop times (the loop is is predefined in asm_pure_loop.S), or it's
>> good to give explanation in comments for these values.
>>
>>> +
>>> +err=$?
>>> +exit $err
>>> diff --git a/tools/perf/tests/shell/lib/coresight.sh b/tools/perf/tests/shell/lib/coresight.sh
>>> new file mode 100644
>>> index 000000000000..cd6c1283e6f5
>>> --- /dev/null
>>> +++ b/tools/perf/tests/shell/lib/coresight.sh
>>> @@ -0,0 +1,130 @@
>>> +# SPDX-License-Identifier: GPL-2.0
>>> +# Carsten Haitzler <carsten.haitzler@....com>, 2021
>>> +
>>> +# This is sourced from a driver script so no need for #!/bin... etc. at the
>>> +# top - the assumption below is that it runs as part of sourcing after the
>>> +# test sets up some basic env vars to say what it is.
>>> +
>>> +# perf record options for the perf tests to use
>>> +PERFRECMEM="-m ,128M"
>>
>> We must use 128Mb for the AUX trace buffer?  The big buffer size is
>> not friendly for embedded system.
>>
>>> +PERFRECOPT="$PERFRECMEM -e cs_etm//u"
>>> +
>>> +# These tests need to be run as root or coresight won't allow large buffers
>>> +# and will not collect proper data
>>> +UID=`id -u`
>>> +if test "$UID" -ne 0; then
>>> +	echo "Not running as root... skip"
>>> +	exit 2
>>> +fi
>>> +
>>> +TOOLS=$(dirname $0)/tools
>>> +DIR="$TOOLS/coresight/$TEST"
>>> +BIN="$DIR/$TEST"
>>> +# If the test tool/binary does not exist and is executable then skip the test
>>> +if ! test -x "$BIN"; then exit 2; fi
>>> +DATD="."
>>
>> It's blur to set DATD and STATD to ".".  If the user doesn't specify
>> the envs, it's not clear it will point to which folder.
>>
>>> +# If the data dir env is set then make the data dir use that instead of ./
>>> +if test -n "$PERF_TEST_CORESIGHT_DATADIR"; then
>>> +	DATD="$PERF_TEST_CORESIGHT_DATADIR";
>>> +fi
>>> +# If the stat dir env is set then make the data dir use that instead of ./
>>> +STATD="."
>>> +if test -n "$PERF_TEST_CORESIGHT_STATDIR"; then
>>> +	STATD="$PERF_TEST_CORESIGHT_STATDIR";
>>> +fi
>>> +
>>> +# Called if the test fails - error code 2
>>> +err() {
>>> +	echo "$1"
>>> +	exit 1
>>> +}
>>> +
>>> +# Check that some statistics from our perf
>>> +check_val_min() {
>>> +	STATF="$4"
>>> +	if test "$2" -lt "$3"; then
>>> +		echo ", FAILED" >> "$STATF"
>>> +		err "Sanity check number of $1 is too low ($2 < $3)"
>>> +	fi
>>> +}
>>> +
>>> +perf_dump_aux_verify() {
>>> +	# Some basic checking that the AUX chunk contains some sensible data
>>> +	# to see that we are recording something and at least a minimum
>>> +	# amount of it. We should almost always see F3 atoms in just about
>>> +	# anything but certainly we will see some trace info and async atom
>>> +	# chunks.
>>> +	DUMP="$DATD/perf-tmp-aux-dump.txt"
>>> +	perf report --stdio --dump -i "$1" | \
>>> +		grep -o -e I_ATOM_F3 -e I_ASYNC -e I_TRACE_INFO > "$DUMP"
>>> +	# Simply count how many of these atoms we find to see that we are
>>> +	# producing a reasonable amount of data - exact checks are not sane
>>> +	# as this is a lossy  process where we may lose some blocks and the
>>> +	# compiler may produce different code depending on the compiler and
>>> +	# optimization options, so this is rough  just to see if we're
>>> +	# either missing almost all the data or all of it
>>> +	ATOM_F3_NUM=`grep I_ATOM_F3 "$DUMP" | wc -l`
>>> +	ATOM_ASYNC_NUM=`grep I_ASYNC "$DUMP" | wc -l`
>>> +	ATOM_TRACE_INFO_NUM=`grep I_TRACE_INFO "$DUMP" | wc -l`
>>> +	rm -f "$DUMP"
>>> +
>>> +	# Arguments provide minimums for a pass
>>> +	CHECK_F3_MIN="$2"
>>> +	CHECK_ASYNC_MIN="$3"
>>> +	CHECK_TRACE_INFO_MIN="$4"
>>> +
>>> +	# Write out statistics, so over time you can track results to see if
>>> +	# there is a pattern - for example we have less "noisy" results that
>>> +	# produce more consistent amounts of data each run, to see if over
>>> +	# time any techinques to  minimize data loss are having an effect or
>>> +	# not
>>> +	STATF="$STATD/stats-$TEST-$DATV.csv"
>>> +	if ! test -f "$STATF"; then
>>> +		echo "ATOM F3 Count, Minimum, ATOM ASYNC Count, Minimum, TRACE INFO Count, Minimum" > "$STATF"
>>> +	fi
>>> +	echo -n "$ATOM_F3_NUM, $CHECK_F3_MIN, $ATOM_ASYNC_NUM, $CHECK_ASYNC_MIN, $ATOM_TRACE_INFO_NUM, $CHECK_TRACE_INFO_MIN" >> "$STATF"
>>> +
>>> +	# Actually check to see if we passed or failed.
>>> +	check_val_min "ATOM_F3" "$ATOM_F3_NUM" "$CHECK_F3_MIN" "$STATF"
>>> +	check_val_min "ASYNC" "$ATOM_ASYNC_NUM" "$CHECK_ASYNC_MIN" "$STATF"
>>> +	check_val_min "TRACE_INFO" "$ATOM_TRACE_INFO_NUM" "$CHECK_TRACE_INFO_MIN" "$STATF"
>>> +	echo ", Ok" >> "$STATF"
>>> +}
>>> +
>>> +perf_dump_aux_tid_verify() {
>>
>> This function is not used in the test contained in this patch.
>>
>>> +	# Specifically crafted test will produce a list of Tread ID's to
>>> +	# stdout that need to be checked to  see that they have had trace
>>> +	# info collected in AUX blocks in the perf data. This will go
>>> +	# through all the TID's that are listed as CID=0xabcdef and see
>>> +	# that all the Thread IDs the test tool reports are  in the perf
>>> +	# data AUX chunks
>>> +
>>> +	# The TID test tools will print a TID per stdout line that are being
>>> +	# tested
>>> +	TIDS=`cat "$2"`
>>> +	# Scan the perf report to find the TIDs that are actually CID in hex
>>> +	# and build a list of the ones found
>>> +	FOUND_TIDS=`perf report --stdio --dump -i "$1" | \
>>> +			grep -o "CID=0x[0-9a-z]\+" | sed 's/CID=//g' | \
>>> +			uniq | sort | uniq`
>>> +
>>> +	# Iterate over the list of TIDs that the test says it has and find
>>> +	# them in the TIDs found in the perf report
>>> +	MISSING=""
>>> +	for TID2 in $TIDS; do
>>> +		FOUND=""
>>> +		for TIDHEX in $FOUND_TIDS; do
>>> +			TID=`printf "%i" $TIDHEX`
>>> +			if test "$TID" -eq "$TID2"; then
>>> +				FOUND="y"
>>> +				break
>>> +			fi
>>> +		done
>>> +		if test -z "$FOUND"; then
>>> +			MISSING="$MISSING $TID"
>>> +		fi
>>> +	done
>>> +	if test -n "$MISSING"; then
>>> +		err "Thread IDs $MISSING not found in perf AUX data"
>>> +	fi
>>> +}
>>> diff --git a/tools/perf/tests/shell/tools/Makefile b/tools/perf/tests/shell/tools/Makefile
>>> new file mode 100644
>>> index 000000000000..c7ada20922fd
>>> --- /dev/null
>>> +++ b/tools/perf/tests/shell/tools/Makefile
>>> @@ -0,0 +1,26 @@
>>> +# SPDX-License-Identifier: GPL-2.0-only
>>> +# Carsten Haitzler <carsten.haitzler@....com>, 2021
>>> +include ../../../../../tools/scripts/Makefile.include
>>> +include ../../../../../tools/scripts/Makefile.arch
>>> +include ../../../../../tools/scripts/utilities.mak
>>
>> To be honest, I don't understand well for perf's build and config
>> system.  Seems to me, a good example for building program is jevents.
>>
>> Please take a look for the code:
>> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/tools/perf/Makefile.perf#n667
>>
>> If follow the same method with jevents for building test programs,
>> I can see one benefit is we don't need to create a Makefile, on the
>> other hand, we can reuse the perf's build system and simply create a
>> Build file under the folder tools/perf/tests/shell/.../coresight/.
>>
>>> +
>>> +SUBDIRS = \
>>> +	coresight
>>> +
>>> +all: $(SUBDIRS)
>>> +$(SUBDIRS):
>>> +	$(Q)$(MAKE) -C $@
>>> +
>>> +INSTALLDIRS = $(SUBDIRS:%=install-%)
>>> +
>>> +install-tests: all $(INSTALLDIRS)
>>> +$(INSTALLDIRS):
>>> +	$(Q)$(MAKE) -C $(@:install-%=%) install-tests
>>> +
>>> +CLEANDIRS = $(SUBDIRS:%=clean-%)
>>> +
>>> +clean: $(CLEANDIRS)
>>> +$(CLEANDIRS):
>>> +	$(Q)$(MAKE) -C $(@:clean-%=%) O=$(OUTPUT) clean >/dev/null
>>> +
>>> +.PHONY: all clean install-tests $(SUBDIRS) $(CLEANDIRS) $(INSTALLDIRS)
>>> diff --git a/tools/perf/tests/shell/tools/coresight/Makefile b/tools/perf/tests/shell/tools/coresight/Makefile
>>> new file mode 100644
>>> index 000000000000..723006ea827c
>>> --- /dev/null
>>> +++ b/tools/perf/tests/shell/tools/coresight/Makefile
>>> @@ -0,0 +1,27 @@
>>> +# SPDX-License-Identifier: GPL-2.0-only
>>> +# Carsten Haitzler <carsten.haitzler@....com>, 2021
>>> +include ../../../../../../tools/scripts/Makefile.include
>>> +include ../../../../../../tools/scripts/Makefile.arch
>>> +include ../../../../../../tools/scripts/utilities.mak
>>> +
>>> +SUBDIRS = \
>>> +	asm_pure_loop
>>> +
>>> +all: $(SUBDIRS)
>>> +$(SUBDIRS):
>>> +	$(Q)$(MAKE) -C $@
>>> +
>>> +INSTALLDIRS = $(SUBDIRS:%=install-%)
>>> +
>>> +install-tests: $(INSTALLDIRS)
>>> +$(INSTALLDIRS):
>>> +	$(Q)$(MAKE) -C $(@:install-%=%) install-tests
>>> +
>>> +CLEANDIRS = $(SUBDIRS:%=clean-%)
>>> +
>>> +clean: $(CLEANDIRS)
>>> +$(CLEANDIRS):
>>> +	$(Q)$(MAKE) -C $(@:clean-%=%) clean >/dev/null
>>> +
>>> +.PHONY: all clean $(SUBDIRS) $(CLEANDIRS) $(INSTALLDIRS)
>>> +
>>> diff --git a/tools/perf/tests/shell/tools/coresight/Makefile.miniconfig b/tools/perf/tests/shell/tools/coresight/Makefile.miniconfig
>>> new file mode 100644
>>> index 000000000000..cedd26c6a0eb
>>> --- /dev/null
>>> +++ b/tools/perf/tests/shell/tools/coresight/Makefile.miniconfig
>>> @@ -0,0 +1,23 @@
>>> +# SPDX-License-Identifier: GPL-2.0-only
>>> +# Carsten Haitzler <carsten.haitzler@....com>, 2021
>>> +
>>> +ifndef DESTDIR
>>> +prefix ?= $(HOME)
>>> +endif
>>> +
>>> +DESTDIR_SQ = $(subst ','\'',$(DESTDIR))
>>> +perfexecdir = libexec/perf-core
>>> +perfexec_instdir = $(perfexecdir)
>>> +
>>> +ifneq ($(filter /%,$(firstword $(perfexecdir))),)
>>> +perfexec_instdir = $(perfexecdir)
>>> +else
>>> +perfexec_instdir = $(prefix)/$(perfexecdir)
>>> +endif
>>> +
>>> +perfexec_instdir_SQ = $(subst ','\'',$(perfexec_instdir))
>>> +INSTALL = install
>>> +
>>> +include ../../../../../../scripts/Makefile.include
>>> +include ../../../../../../scripts/Makefile.arch
>>> +include ../../../../../../scripts/utilities.mak
>>
>> As suggested above, if we refer the building method of jevent, I think
>> this Makefile.miniconfig is not needed anymore.
>>
>>> diff --git a/tools/perf/tests/shell/tools/coresight/asm_pure_loop/Makefile b/tools/perf/tests/shell/tools/coresight/asm_pure_loop/Makefile
>>> new file mode 100644
>>> index 000000000000..10c5a60cb71c
>>> --- /dev/null
>>> +++ b/tools/perf/tests/shell/tools/coresight/asm_pure_loop/Makefile
>>> @@ -0,0 +1,30 @@
>>> +# SPDX-License-Identifier: GPL-2.0
>>> +# Carsten Haitzler <carsten.haitzler@....com>, 2021
>>> +
>>> +include ../Makefile.miniconfig
>>> +
>>> +BIN=asm_pure_loop
>>> +LIB=
>>> +
>>> +all: $(BIN)
>>> +
>>> +$(BIN): $(BIN).S
>>> +ifdef CORESIGHT
>>> +ifeq ($(ARCH),arm64)
>>> +	$(Q)$(CC) $(BIN).S -nostdlib -static -o $(BIN) $(LIB)
>>> +endif
>>> +endif
>>> +
>>> +install-tests: all
>>> +ifdef CORESIGHT
>>> +ifeq ($(ARCH),arm64)
>>> +	$(call QUIET_INSTALL, tests) \
>>> +		$(INSTALL) -d -m 755 '$(DESTDIR_SQ)$(perfexec_instdir_SQ)/tests/shell/tools/$(BIN)'; \
>>> +		$(INSTALL) $(BIN) '$(DESTDIR_SQ)$(perfexec_instdir_SQ)/tests/shell/tools/$(BIN)/$(BIN)'
>>> +endif
>>> +endif
>>> +
>>> +clean:
>>> +	$(Q)$(RM) -f $(BIN)
>>> +
>>> +.PHONY: all clean install-tests
>>> diff --git a/tools/perf/tests/shell/tools/coresight/asm_pure_loop/asm_pure_loop.S b/tools/perf/tests/shell/tools/coresight/asm_pure_loop/asm_pure_loop.S
>>> new file mode 100644
>>> index 000000000000..262876451021
>>> --- /dev/null
>>> +++ b/tools/perf/tests/shell/tools/coresight/asm_pure_loop/asm_pure_loop.S
>>> @@ -0,0 +1,28 @@
>>> +/* SPDX-License-Identifier: GPL-2.0 */
>>> +/* Tamas Zsoldos <tamas.zsoldos@....com>, 2021 */
>>> +
>>> +.globl _start
>>> +_start:
>>> +	mov	x0, 0x000fffff
>>> +	mov	x1, xzr
>>> +loop:
>>> +	nop
>>> +	nop
>>> +	cbnz	x1, noskip
>>> +	nop
>>> +	nop
>>> +	adrp	x2, skip
>>> +	add 	x2, x2, :lo12:skip
>>> +	br	x2
>>> +	nop
>>> +	nop
>>> +noskip:
>>> +	nop
>>> +	nop
>>> +skip:
>>> +	sub	x0, x0, 1
>>> +	cbnz	x0, loop
>>> +
>>> +	mov	x0, #0
>>> +	mov	x8, #93 // __NR_exit syscall
>>> +	svc	#0
>>
>> I verified this code on Arm64 machine and it works!
>>
>> I am a bit worry about the code for using the hard code number for
>> system call.  Another option is to use the inline assembly
>> in C code, I think you have considered for this approach, this might
>> introduce noise for extra branch instructions during the testing,
>> but it can allow us to program standard C program (and don't worry
>> about the program exiting).
>>
>> If you think using assembly code is better than inline assembly, it
>> would be fine for me.  Eventually, the system call number is very
>> seldomly to be changed.
>>
>> Thanks,
>> Leo
> 

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