Message-ID: <4fad02f2-6460-0726-f33b-0e2dc3df05ca@foss.arm.com>
Date:   Tue, 4 Jan 2022 15:14:15 +0000
MIME-Version: 1.0
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Subject: Re: [PATCH 04/12] perf test: Add beginning of test infra + test to
 exercise coresight
Content-Language: en-US
To:     Leo Yan <leo.yan@linaro.org>
Cc:     linux-kernel@vger.kernel.org, coresight@lists.linaro.org,
        suzuki.poulose@arm.com, mathieu.poirier@linaro.org,
        mike.leach@linaro.org, inux-perf-users@vger.kernel.org,
        acme@kernel.org
References: <20211215160403.69264-1-carsten.haitzler@foss.arm.com>
 <20211215160403.69264-4-carsten.haitzler@foss.arm.com>
 <20211221150349.GB41974@leoy-ThinkPad-X240s>
From:   Carsten Haitzler <carsten.haitzler@foss.arm.com>
Organization: Arm Ltd.
In-Reply-To: <20211221150349.GB41974@leoy-ThinkPad-X240s>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit
Precedence: bulk


On 12/21/21 15:03, Leo Yan wrote:
> Hi Carsten,
> 
> On Wed, Dec 15, 2021 at 04:03:55PM +0000, carsten.haitzler@foss.arm.com wrote:
>> From: Carsten Haitzler <carsten.haitzler@arm.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@arm.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/
> 
> I'd like to leave this question for Arnaldo / Jiri for the folder
> layout.

Personally - I'm not fussed. :) So whatever you think is best.

>> 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@arm.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 $err
>> diff --git a/tools/perf/tests/shell/lib/coresight.sh b/tools/perf/tests/shell/lib/coresight.sh
>> new file mode 100644
>> index 000000000000..cd6c1283e6f5
>> --- /dev/null
>> +++ b/tools/perf/tests/shell/lib/coresight.sh
>> @@ -0,0 +1,130 @@
>> +# SPDX-License-Identifier: GPL-2.0
>> +# Carsten Haitzler <carsten.haitzler@arm.com>, 2021
>> +
>> +# This is sourced from a driver script so no need for #!/bin... etc. at the
>> +# top - the assumption below is that it runs as part of sourcing after the
>> +# test sets up some basic env vars to say what it is.
>> +
>> +# perf record options for the perf tests to use
>> +PERFRECMEM="-m ,128M"
> 
> We must use 128Mb for the AUX trace buffer?  The big buffer size is
> not friendly for embedded system.
> 
>> +PERFRECOPT="$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@arm.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@arm.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@arm.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@arm.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@arm.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