Re: [PATCH] selftests/ftrace: Differentiate bash and dash in dynevent_limitations.tc

On 4/15/25 16:58, Masami Hiramatsu (Google) wrote:

On Mon, 14 Apr 2025 21:09:00 -0400 Steven Rostedt rostedt@goodmis.org wrote:

...

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.

Thanks for fixing this issue!

Acked-by: Masami Hiramatsu (Google) mhiramat@kernel.org

Steve, do you want me to pick this up for rc3?

thanks, -- Shuah