| Message ID | 20250414210900.4de5e8b9@gandalf.local.home (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | selftests/ftrace: Differentiate bash and dash in dynevent_limitations.tc | expand |
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> Thank you! > 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.uk/ > 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 "$TEST_STRING" >> dynamic_events > echo > dynamic_events > -- > 2.47.2 >
On 4/15/25 16:58, Masami Hiramatsu (Google) wrote: > On Mon, 14 Apr 2025 21:09:00 -0400 > Steven Rostedt <rostedt@goodmis.org> wrote: > >> From: Steven Rostedt <rostedt@goodmis.org> >> >> bash and dash evaluate variables differently. >> dash will evaluate '\\' every time it is read whereas bash does not. >> >> TEST_STRING="$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
On Tue, 15 Apr 2025 17:03:44 -0600 Shuah Khan <skhan@linuxfoundation.org> wrote: > > Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org> > > > > Steve, do you want me to pick this up for rc3? Hi Shuah, Yes, can you please. But can you change the Closes tag to: Closes: https://lore.kernel.org/all/350786cc-9e40-4396-ab95-4f10d69122fb@sirena.org.uk/ Because the one I had was the top of the thread which is about a different bug. Mark mentioned this bug in the middle of the thread and the above link is where Mark mentioned it. -- Steve
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