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

[Shuah Khan]

On 4/15/25 16:58, Masami Hiramatsu (Google) wrote:
> On Mon, 14 Apr 2025 21:09:00 -0400
> Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:
>
> > From: Steven Rostedt <rostedt@xxxxxxxxxxx>
> >
> > 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@xxxxxxxxxx>

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

thanks,
-- Shuah