perf test buildid: Fix shell string substitutions

The perf test named “build id cache operations” skips with below error
on some distros:

  <<>>
   78: build id cache operations                                       :
  test child forked, pid 111101
  WARNING: wine not found. PE binaries will not be run.
  test binaries: /tmp/perf.ex.SHA1.PKz /tmp/perf.ex.MD5.Gt3 ./tests/shell/../pe-file.exe
  DEBUGINFOD_URLS=
  Adding 4abd406f041feb4f10ecde3fc30fd0639e1a91cb /tmp/perf.ex.SHA1.PKz: Ok
  build id: 4abd406f041feb4f10ecde3fc30fd0639e1a91cb
  ./tests/shell/buildid.sh: 69: ./tests/shell/buildid.sh: Bad substitution
  test child finished with -2
  build id cache operations: Skip
  <<>>

The test script "tests/shell/buildid.sh" uses some of the string
substitution ways which are supported in bash, but not in "sh" or other
shells. Above error on line number 69 that reports "Bad substitution"
is:

  <<>>
  link=${build_id_dir}/.build-id/${id:0:2}/${id:2}
  <<>>

Here the way of getting first two characters from id ie, ${id:0:2} and
similarly expressions like ${id:2} is not recognised in "sh". So the
line errors and instead of hitting failure, the test gets skipped as
shown in logs.  So the syntax issue causes test not to be executed in
such cases. Similarly usage : "${@: -1}" [ to pick last argument passed
to a function] in “test_record” doesn’t work in all distros.

Fix this by using alternative way with shell substitution to pick
required characters from the string. Also fix the usage of “${@: -1}” to
work in all cases.

Another usage in “test_record” is:

  <<>>
  ${perf} record --buildid-all -o ${data} $@ &> ${log}
  <<>>

This causes the 'perf record' to start in background and Results in the
data file not being created by the time "check" function is invoked.
Below log shows 'perf record' result getting displayed after the call to
"check" function.

  <<>>
  running: perf record /tmp/perf.ex.SHA1.EAU
  build id: 4abd406f041feb4f10ecde3fc30fd0639e1a91cb
  link: /tmp/perf.debug.mLT/.build-id/4a/bd406f041feb4f10ecde3fc30fd0639e1a91cb
  failed: link /tmp/perf.debug.mLT/.build-id/4a/bd406f041feb4f10ecde3fc30fd0639e1a91cb does not exist
  test child finished with -1
  build id cache operations: FAILED!
  root@machine:~/athira/linux/tools/perf# Couldn't synthesize bpf events.
  [ perf record: Woken up 1 times to write data ]
  [ perf record: Captured and wrote 0.010 MB /tmp/perf.data.bFF ]
  <<>>

Fix this by redirecting output instead of using “&” which starts the
command in background.
Reviewed-by: David Laight <David.Laight@ACULAB.COM>
Signed-off-by: Athira Jajeev <atrajeev@linux.vnet.ibm.com>
Tested-by: Disha Goel <disgoel@linux.ibm.com>
Acked-by: Ian Rogers <irogers@google.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: James Clark <james.clark@arm.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kajol Jain <kjain@linux.ibm.com>
Cc: Madhavan Srinivasan <maddy@linux.ibm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Nageswara R Sastry <rnsastry@linux.ibm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: linuxppc-dev@lists.ozlabs.org
Link: https://lore.kernel.org/r/20230119142719.32628-1-atrajeev@linux.vnet.ibm.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/tests/shell/buildid.sh

@@ -66,7 +66,9 @@ check()
 	esac
 	echo "build id: ${id}"
 
-	link=${build_id_dir}/.build-id/${id:0:2}/${id:2}
+	id_file=${id#??}
+	id_dir=${id%$id_file}
+	link=$build_id_dir/.build-id/$id_dir/$id_file
 	echo "link: ${link}"
 
 	if [ ! -h $link ]; then
@@ -74,7 +76,7 @@ check()
 		exit 1
 	fi
 
-	file=${build_id_dir}/.build-id/${id:0:2}/`readlink ${link}`/elf
+	file=${build_id_dir}/.build-id/$id_dir/`readlink ${link}`/elf
 	echo "file: ${file}"
 
 	# Check for file permission of original file
@@ -130,20 +132,22 @@ test_record()
 {
 	data=$(mktemp /tmp/perf.data.XXX)
 	build_id_dir=$(mktemp -d /tmp/perf.debug.XXX)
-	log=$(mktemp /tmp/perf.log.XXX)
+	log_out=$(mktemp /tmp/perf.log.out.XXX)
+	log_err=$(mktemp /tmp/perf.log.err.XXX)
 	perf="perf --buildid-dir ${build_id_dir}"
 
 	echo "running: perf record $@"
-	${perf} record --buildid-all -o ${data} $@ &> ${log}
+	${perf} record --buildid-all -o ${data} $@ 1>${log_out} 2>${log_err}
 	if [ $? -ne 0 ]; then
 		echo "failed: record $@"
-		echo "see log: ${log}"
+		echo "see log: ${log_err}"
 		exit 1
 	fi
 
-	check ${@: -1}
+	args="$*"
+	check ${args##* }
 
-	rm -f ${log}
+	rm -f ${log_out} ${log_err}
 	rm -rf ${build_id_dir}
 	rm -rf ${data}
 }