selftests/ftrace: Use printf for backslash included command

Since the built-in echo has different behavior in POSIX shell
(dash) and bash, kprobe_syntax_errors.tc can fail on dash which
interpret backslash escape automatically.

To fix this issue, we explicitly use printf "%s" (not interpret
backslash escapes) if the command string can include backslash.

Reported-by: Liu Yiding <[email protected]>
Suggested-by: Xiao Yang <[email protected]>
Signed-off-by: Masami Hiramatsu <[email protected]>
Signed-off-by: Shuah Khan <[email protected]>

Author: mhiramat

tools/testing/selftests/ftrace/test.d/functions

@@ -119,12 +119,14 @@ yield() {
     ping $LOCALHOST -c 1 || sleep .001 || usleep 1 || sleep 1
 }
 
+# Since probe event command may include backslash, explicitly use printf "%s"
+# to NOT interpret it.
 ftrace_errlog_check() { # err-prefix command-with-error-pos-by-^ command-file
-    pos=$(echo -n "${2%^*}" | wc -c) # error position
-    command=$(echo "$2" | tr -d ^)
+    pos=$(printf "%s" "${2%^*}" | wc -c) # error position
+    command=$(printf "%s" "$2" | tr -d ^)
     echo "Test command: $command"
     echo > error_log
-    (! echo "$command" >> "$3" ) 2> /dev/null
+    (! printf "%s" "$command" >> "$3" ) 2> /dev/null
     grep "$1: error:" -A 3 error_log
     N=$(tail -n 1 error_log | wc -c)
     # "  Command: " and "^\n" => 13

tools/testing/selftests/ftrace/test.d/kprobe/kprobe_syntax_errors.tc

@@ -91,7 +91,9 @@ esac
 if grep -q "Create/append/" README && grep -q "imm-value" README; then
 echo 'p:kprobes/testevent _do_fork' > kprobe_events
 check_error '^r:kprobes/testevent do_exit'	# DIFF_PROBE_TYPE
-echo 'p:kprobes/testevent _do_fork abcd=\1' > kprobe_events
+
+# Explicitly use printf "%s" to not interpret \1
+printf "%s" 'p:kprobes/testevent _do_fork abcd=\1' > kprobe_events
 check_error 'p:kprobes/testevent _do_fork ^bcd=\1'	# DIFF_ARG_TYPE
 check_error 'p:kprobes/testevent _do_fork ^abcd=\1:u8'	# DIFF_ARG_TYPE
 check_error 'p:kprobes/testevent _do_fork ^abcd=\"foo"'	# DIFF_ARG_TYPE