From: Steven Rostedt rostedt@goodmis.org
bash and dash evaluate variables differently. dash will evaluate '\' every time it is read whereas bash does not.
TEST_STRING="$TEST_STRING \$i" echo $TEST_STRING
With i=123 On bash, that will print "\123" but on dash, that will print the escape sequence of \123 as the \ will be interpreted again in the echo.
The dynevent_limitations.tc test created a very large list of arguments to test the maximum number of arguments to pass to the dynamic events file. It had a loop of:
TEST_STRING=$1 # Acceptable for i in `seq 1 $MAX_ARGS`; do TEST_STRING="$TEST_STRING \$i" done echo "$TEST_STRING" >> dynamic_events
This worked fine on bash, but when run on dash it failed.
This was due to dash interpreting the "\$i" twice. Once when it was assigned to TEST_STRING and a second time with the echo $TEST_STRING.
bash does not process the backslash more than the first time.
To solve this, assign a double backslash to a variable "bs" and then echo it to "ts". If "ts" changes, it is dash, if not, it is bash. Then update "bs" accordingly, and use that to assign TEST_STRING.
Now this could possibly just check if "$BASH" is defined or not, but this is testing if the issue exists and not just which shell is being used.
Fixes: 581a7b26ab364 ("selftests/ftrace: Add dynamic events argument limitation test case") Reported-by: Mark Brown broonie@kernel.org Closes: https://lore.kernel.org/all/ccc40f2b-4b9e-4abd-8daf-d22fce2a86f0@sirena.org.... Signed-off-by: Steven Rostedt (Google) rostedt@goodmis.org --- .../test.d/dynevent/dynevent_limitations.tc | 23 ++++++++++++++++++- 1 file changed, 22 insertions(+), 1 deletion(-)
diff --git a/tools/testing/selftests/ftrace/test.d/dynevent/dynevent_limitations.tc b/tools/testing/selftests/ftrace/test.d/dynevent/dynevent_limitations.tc index 6b94b678741a..885631c02623 100644 --- a/tools/testing/selftests/ftrace/test.d/dynevent/dynevent_limitations.tc +++ b/tools/testing/selftests/ftrace/test.d/dynevent/dynevent_limitations.tc @@ -7,11 +7,32 @@ MAX_ARGS=128 EXCEED_ARGS=$((MAX_ARGS + 1))
+# bash and dash evaluate variables differently. +# dash will evaluate '\' every time it is read whereas bash does not. +# +# TEST_STRING="$TEST_STRING \$i" +# echo $TEST_STRING +# +# With i=123 +# On bash, that will print "\123" +# but on dash, that will print the escape sequence of \123 as the \ will +# be interpreted again in the echo. +# +# Set a variable "bs" to save a double backslash, then echo that +# to "ts" to see if $ts changed or not. If it changed, it's dash, +# if not, it's bash, and then bs can equal a single backslash. +bs='\' +ts=`echo $bs` +if [ "$ts" = '\' ]; then + # this is bash + bs='' +fi + check_max_args() { # event_header TEST_STRING=$1 # Acceptable for i in `seq 1 $MAX_ARGS`; do - TEST_STRING="$TEST_STRING \$i" + TEST_STRING="$TEST_STRING $bs$i" done echo "$TEST_STRING" >> dynamic_events echo > dynamic_events