On Mon, 14 Apr 2025 21:09:00 -0400 Steven Rostedt <[email protected]> wrote:
> From: Steven Rostedt <[email protected]> > > 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) <[email protected]> Thank you! > Fixes: 581a7b26ab364 ("selftests/ftrace: Add dynamic events argument > limitation test case") > Reported-by: Mark Brown <[email protected]> > Closes: > https://lore.kernel.org/all/[email protected]/ > Signed-off-by: Steven Rostedt (Google) <[email protected]> > --- > .../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 > -- > 2.47.2 > -- Masami Hiramatsu (Google) <[email protected]>
