Re: [PATCH v2 17/19] test: Add a pid-USDT test

[Kris Van Hees <kris.van.hees@oracle.com>]

On Fri, Oct 04, 2024 at 12:51:57AM -0400, eugene.loh@oracle.com wrote:
> From: Eugene Loh <eugene.loh@oracle.com>
> 
> This checks that pid entry, pid return, pid offset, USDT, and USDT
> is-enabled probes can all coexist.  Specifically, pid offset probes
> can sit on the same PCs as pid entry, USDT, and USDT is-enabled
> probes.
> 
> Note that PCs for pid return probes are apparently in the caller
> function.  I guess that's due to using uretprobe.  I'm not convinced
> yet that that isn't a bug.  It isn't what Solaris did.

This is not a bug - the implementation of uretprobe is such that it fires
*after* the return has taken place because it is implemented by means of a
trampoline function that is interposed in the return path by replacing the
real return address with the address of a uretprobe trampoline that triggers
the uretprobe firing.

The alternative would require setting a regular uprobe on every return
instruction in the function (we used to do that in our custom FBT probe
implementation in the previous version).

I would update this last paragraph to be:

	Note that PCs for pid return probes are in the caller function
	due to the uretprobe implementation in the kernel.

> Signed-off-by: Eugene Loh <eugene.loh@oracle.com>

with that ...

Reviewed-by: Kris Van Hees <kris.van.hees@oracle.com>

> ---
>  test/unittest/usdt/tst.pidprobes.r  |   1 +
>  test/unittest/usdt/tst.pidprobes.sh | 292 ++++++++++++++++++++++++++++
>  2 files changed, 293 insertions(+)
>  create mode 100644 test/unittest/usdt/tst.pidprobes.r
>  create mode 100755 test/unittest/usdt/tst.pidprobes.sh
> 
> diff --git a/test/unittest/usdt/tst.pidprobes.r b/test/unittest/usdt/tst.pidprobes.r
> new file mode 100644
> index 000000000..2e9ba477f
> --- /dev/null
> +++ b/test/unittest/usdt/tst.pidprobes.r
> @@ -0,0 +1 @@
> +success
> diff --git a/test/unittest/usdt/tst.pidprobes.sh b/test/unittest/usdt/tst.pidprobes.sh
> new file mode 100755
> index 000000000..8d18c89a4
> --- /dev/null
> +++ b/test/unittest/usdt/tst.pidprobes.sh
> @@ -0,0 +1,292 @@
> +#!/bin/bash
> +#
> +# Oracle Linux DTrace.
> +# Copyright (c) 2024, Oracle and/or its affiliates. All rights reserved.
> +# Licensed under the Universal Permissive License v 1.0 as shown at
> +# http://oss.oracle.com/licenses/upl.
> +#
> +# This test verifies that USDT and pid probes can share underlying probes.
> +
> +dtrace=$1
> +
> +# Set up test directory.
> +
> +DIRNAME=$tmpdir/pidprobes.$$.$RANDOM
> +mkdir -p $DIRNAME
> +cd $DIRNAME
> +
> +# Create test source files.
> +
> +cat > prov.d <<EOF
> +provider pyramid {
> +	probe entry(int, char, int, int);
> +};
> +EOF
> +
> +cat > main.c <<EOF
> +#include <stdio.h>
> +#include "prov.h"
> +
> +void foo() {
> +	int n = 0;
> +
> +	PYRAMID_ENTRY(2, 'a', 16, 128);
> +	if (PYRAMID_ENTRY_ENABLED())
> +		n += 2;
> +	PYRAMID_ENTRY(4, 'b', 32, 256);
> +	if (PYRAMID_ENTRY_ENABLED())
> +		n += 8;
> +	printf("my result: %d\n", n);
> +}
> +
> +int
> +main(int argc, char **argv)
> +{
> +	foo();
> +}
> +EOF
> +
> +# Build the test program.
> +
> +$dtrace -h -s prov.d
> +if [ $? -ne 0 ]; then
> +	echo "failed to generate header file" >&2
> +	exit 1
> +fi
> +cc $test_cppflags -c main.c
> +if [ $? -ne 0 ]; then
> +	echo "failed to compile test" >&2
> +	exit 1
> +fi
> +if [[ `uname -m` = "aarch64" ]]; then
> +	objdump -d main.o > disasm_foo.txt.before
> +fi
> +$dtrace -G -64 -s prov.d main.o
> +if [ $? -ne 0 ]; then
> +	echo "failed to create DOF" >&2
> +	exit 1
> +fi
> +cc $test_cppflags -o main main.o prov.o
> +if [ $? -ne 0 ]; then
> +	echo "failed to link final executable" >&2
> +	exit 1
> +fi
> +
> +# Check that the program output is 0 when the USDT probe is not enabled.
> +# That is, the PYRAMID_ENTRY_ENABLED() is-enabled checks should not pass.
> +
> +./main > main.out
> +echo "my result: 0" > main.out.expected
> +if ! diff -q main.out main.out.expected > /dev/null; then
> +	echo '"my result"' looks wrong when not using DTrace
> +	echo === got ===
> +	cat main.out
> +	echo === expected ===
> +	cat main.out.expected
> +	exit 1
> +fi
> +
> +# Run dtrace.
> +
> +$dtrace $dt_flags -q -c ./main -o dtrace.out -n '
> +p*d$target::foo:
> +{
> +	printf("%d %s:%s:%s:%s %x\n", pid, probeprov, probemod, probefunc, probename, uregs[R_PC]);
> +}' > main.out2
> +if [ $? -ne 0 ]; then
> +	echo "failed to run dtrace" >&2
> +	cat main.out2
> +	cat dtrace.out
> +	exit 1
> +fi
> +echo "my result: 10" > main.out2.expected
> +if ! diff -q main.out2 main.out2.expected > /dev/null; then
> +	echo '"my result"' looks wrong when using DTrace
> +	echo === got ===
> +	cat main.out2
> +	echo === expected ===
> +	cat main.out2.expected
> +	exit 1
> +fi
> +
> +# Check that the program output is 10 when the USDT probe is enabled.
> +# That is, the PYRAMID_ENTRY_ENABLED() is-enabled checks should pass.
> +
> +echo "my result: 10" > main.out2.expected
> +
> +if ! diff -q main.out2 main.out2.expected > /dev/null; then
> +	echo '"my result"' looks wrong
> +	echo === got ===
> +	cat main.out2
> +	echo === expected ===
> +	cat main.out2.expected
> +	exit 1
> +fi
> +
> +# Get the reported pid.
> +
> +if [ `awk 'NF != 0 { print $1 }' dtrace.out | uniq | wc -l` -ne 1 ]; then
> +	echo no unique pid
> +	cat dtrace.out
> +	exit 1
> +fi
> +pid=`awk 'NF != 0 { print $1 }' dtrace.out | uniq`
> +
> +# Disassemble foo().
> +
> +objdump -d main | awk '
> +BEGIN { use = 0 }             # start by not printing lines
> +use == 1 && NF == 0 { exit }  # if printing lines but hit a blank, then exit
> +use == 1 { print }            # print lines
> +/<foo>:/ { use = 1 }          # turn on printing when we hit "<foo>:" (without printing this line itself)
> +' > disasm_foo.txt
> +
> +# From the disassembly, get the PCs for foo()'s instructions.
> +
> +pcs=`awk '{print strtonum("0x"$1)}' disasm_foo.txt`
> +pc0=`echo $pcs | awk '{print $1}'`
> +
> +# From the disassembly, get the PCs for USDT probes.
> +# Check libdtrace/dt_link.c's arch-dependent dt_modtext() to see
> +# what sequence of instructions signal a USDT probe.
> +
> +if [[ `uname -m` = "x86_64" ]]; then
> +
> +	# It is the first of five nop instructions in a row.
> +	# So track pc[-6], pc[-5], pc[-4], pc[-3], pc[-2], pc[-1], pc[0]
> +	# as well as whether they are nop.
> +
> +	usdt_pcs_all=`awk '
> +	BEGIN {
> +		pc6 = -1; is_nop6 = 0;
> +		pc5 = -1; is_nop5 = 0;
> +		pc4 = -1; is_nop4 = 0;
> +		pc3 = -1; is_nop3 = 0;
> +		pc2 = -1; is_nop2 = 0;
> +		pc1 = -1; is_nop1 = 0;
> +	}
> +	{
> +		# pc0 is current instruction
> +		pc0 = strtonum("0x"$1);
> +
> +		# decide whether it is a nop
> +		is_nop0 = 0;
> +		if (NF == 3 &&
> +		    $2 == "90" &&
> +		    $3 == "nop")
> +			is_nop0 = 1;
> +
> +		# report if pc[-5] is a USDT instruction
> +		if (is_nop6 == 0 &&
> +		    is_nop5 == 1 &&
> +		    is_nop4 == 1 &&
> +		    is_nop3 == 1 &&
> +		    is_nop2 == 1 &&
> +		    is_nop1 == 1 &&
> +		    is_nop0 == 0)
> +			print pc5;
> +
> +		# prepare advance to next instruction
> +		pc6 = pc5;  is_nop6 = is_nop5;
> +		pc5 = pc4;  is_nop5 = is_nop4;
> +		pc4 = pc3;  is_nop4 = is_nop3;
> +		pc3 = pc2;  is_nop3 = is_nop2;
> +		pc2 = pc1;  is_nop2 = is_nop1;
> +		pc1 = pc0;  is_nop1 = is_nop0;
> +	}' disasm_foo.txt`
> +
> +	# We expect 4 USDT probes (2 USDT and 2 is-enabled).
> +	if [ `echo $usdt_pcs_all | awk '{print NF}'` -ne 4 ]; then
> +		echo ERROR: expected 4 USDT probes but got $usdt_pcs_all
> +		cat disasm_foo.txt
> +		exit 1
> +	fi
> +
> +	# Separate them into regular and is-enabled PCs.
> +	# We assume they alternate.
> +	usdt_pcs=`echo $usdt_pcs_all | awk '{ print $1, $3 }'`
> +	usdt_pcs_isenabled=`echo $usdt_pcs_all | awk '{ print $2, $4 }'`
> +
> +elif [[ `uname -m` = "aarch64" ]]; then
> +
> +	# The initial compilation of foo() makes it obvious where the
> +	# USDT probes are.  We just have to add the function offset in.
> +	usdt_pcs=`awk '/<__dtrace_pyramid___entry>/ { print strtonum("0x"$1) + '$pc0' }' disasm_foo.txt.before`
> +	usdt_pcs_isenabled=`awk '/<__dtraceenabled_pyramid___entry>/ { print strtonum("0x"$1) + '$pc0' }' disasm_foo.txt.before`
> +
> +	# We expect 4 USDT probes (2 USDT and 2 is-enabled).
> +	if [ `echo $usdt_pcs | awk '{print NF}'` -ne 2 -o \
> +	     `echo $usdt_pcs_isenabled | awk '{print NF}'` -ne 2 ]; then
> +		echo ERROR: expected 4 USDT probes but got $usdt_pcs and $usdt_pcs_isenabled
> +		cat disasm_foo.txt.before
> +		exit 1
> +	fi
> +
> +else
> +	echo ERROR unrecognized machine hardware name
> +	exit 1
> +fi
> +
> +# We expect all of the USDT probe PCs to be among the PCs in objdump output.
> +
> +for pc in $usdt_pcs $usdt_pcs_isenabled; do
> +	if echo $pcs | grep -q -vw $pc ; then
> +		echo ERROR: cannot find USDT PC $pc in $pcs
> +		exit 1
> +	fi
> +done
> +
> +# Get the PC for the pid return probe.  (Just keep it in hex.)
> +
> +pc_return=`awk '/'$pid' pid'$pid':main:foo:return/ { print $NF }' dtrace.out`
> +
> +objdump -d main | awk '
> +/^[0-9a-f]* <.*>:$/ { myfunc = $NF }         # enter a new function
> +/^ *'$pc_return'/ { print myfunc; exit(0) }  # report the function $pc_return is in
> +' > return_func.out
> +
> +echo "<main>:" > return_func.out.expected    # since we use uretprobe for pid return probes, the PC will be in the caller
> +
> +if ! diff -q return_func.out return_func.out.expected > /dev/null; then
> +	echo ERROR: return PC looks to be in the wrong function
> +	echo === got ===
> +	cat return_func.out
> +	echo === expected ===
> +	cat return_func.out.expected
> +	exit 1
> +fi
> +
> +# Build up a list of expected dtrace output:
> +# - a blank line
> +# - pid entry
> +# - pid return
> +# - pid offset
> +# - two USDT probes (ignore is-enabled probes)
> +
> +echo > dtrace.out.expected
> +printf "$pid pid$pid:main:foo:entry %x\n" $pc0 >> dtrace.out.expected
> +echo   "$pid pid$pid:main:foo:return $pc_return" >> dtrace.out.expected
> +for pc in $pcs; do
> +	printf "$pid pid$pid:main:foo:%x %x\n" $(($pc - $pc0)) $pc >> dtrace.out.expected
> +done
> +echo $usdt_pcs | awk '{printf("'$pid' pyramid'$pid':main:foo:entry %x\n", $1);}' >> dtrace.out.expected
> +echo $usdt_pcs | awk '{printf("'$pid' pyramid'$pid':main:foo:entry %x\n", $2);}' >> dtrace.out.expected
> +
> +# Sort and check.
> +
> +sort dtrace.out          > dtrace.out.sorted
> +sort dtrace.out.expected > dtrace.out.expected.sorted
> +
> +if ! diff -q dtrace.out.sorted dtrace.out.expected.sorted ; then
> +	echo ERROR: dtrace output looks wrong
> +	echo === got ===
> +	cat dtrace.out.sorted
> +	echo === expected ===
> +	cat dtrace.out.expected.sorted
> +	echo === diff ===
> +	diff dtrace.out.sorted dtrace.out.expected.sorted
> +	exit 1
> +fi
> +
> +echo success
> +exit 0
> -- 
> 2.43.5
>