Re: [PATCH v4 2/4] ftrace: Add support for function argument to graph tracer

[Steven Rostedt]

Replying to my email as it appears gmail blocked it. Probably due to all
the escape characters my output had. Resending with that cut out.

Masami, I was sent a message from gmail that it blocked this from you.

If you want to see the original email:

  https://lore.kernel.org/all/20250411151358.1d4fd8c7@xxxxxxxxxxxxxxxxxx/

-- Steve

On Fri, 11 Apr 2025 15:13:58 -0400
Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:

> On Fri, 11 Apr 2025 14:31:32 -0400
> Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:
> 
> > Hmm, I just tested this, and it fails on my box too (I test on a debian VM).
> > 
> > It fails with and without setting it to bash. I'll take a look too.  
> 
> Hmm, maybe it is a bashism.
> 
> The test has this:
> 
>   # Max arguments limitation
>   MAX_ARGS=128
>   EXCEED_ARGS=$((MAX_ARGS + 1))
> 
>   check_max_args() { # event_header
>     TEST_STRING=$1
>     # Acceptable
>     for i in `seq 1 $MAX_ARGS`; do
>       TEST_STRING="$TEST_STRING \\$i"
>     done
>     echo "$TEST_STRING" >> dynamic_events
>     echo > dynamic_events
>     # Error
>     TEST_STRING="$TEST_STRING \\$EXCEED_ARGS"
>     ! echo "$TEST_STRING" >> dynamic_events
>     return 0
>   }
> 
>   # Kprobe max args limitation
>   if grep -q "kprobe_events" README; then
>     check_max_args "p vfs_read"
>   fi
> 
> So I tried manually executing this in bash:
> 
> --------------------------8<--------------------------
> # TEST_STRING='p vfs_read'
> # for i in `seq 1 128`; do TEST_STRING="$TEST_STRING \\$i" ; done
> # echo $TEST_STRING
> p vfs_read \1 \2

[ This  is cut out to see if it doesn't trigger gmail blocking it again! ]

> # echo "$TEST_STRING" >> /sys/kernel/tracing/dynamic_events
> # echo $?
> 0
> # cat /sys/kernel/tracing/dynamic_events
> p:kprobes/p_vfs_read_0 vfs_read arg1=\1

[ This  is cut out to see if it doesn't trigger gmail blocking it again! ]

> -------------------------->8--------------------------  
> 
> Doing the same in dash:
> 
> --------------------------8<--------------------------
> # dash
> # TEST_STRING='p vfs_read'
> # for i in `seq 1 128`; do TEST_STRING="$TEST_STRING \\$i" ; done
> # echo $TEST_STRING
> p vfs_read         \8 \9 	 

[ This  is cut out to see if it doesn't trigger gmail blocking it again! ]

> # echo "$TEST_STRING" >> /sys/kernel/tracing/dynamic_events
> dash: 8: echo: echo: I/O error
> -------------------------->8--------------------------  
> 
> Looks like dash will translate those "\#" into the ASCII equivalent,
> whereas bash does not.
> 
> This patch seems to fix it:
> 
> 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..ebe2a34cbf92 100644
> --- a/tools/testing/selftests/ftrace/test.d/dynevent/dynevent_limitations.tc
> +++ b/tools/testing/selftests/ftrace/test.d/dynevent/dynevent_limitations.tc
> @@ -11,7 +11,7 @@ check_max_args() { # event_header
>    TEST_STRING=$1
>    # Acceptable
>    for i in `seq 1 $MAX_ARGS`; do
> -    TEST_STRING="$TEST_STRING \\$i"
> +    TEST_STRING="$TEST_STRING \\\\$i"
>    done
>    echo "$TEST_STRING" >> dynamic_events
>    echo > dynamic_events
> 
> 
> Masami, you just recently added this test (it's dated March 27th 2025), did
> you mean to write in the ASCII characters? Why the backslash?
> 
> -- Steve