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

[Shuah Khan <skhan@linuxfoundation.org>]

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