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

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Message-Id: <20250414120013.895b0cc99e52c41eb8ec3774@kernel.org>
Date: Mon, 14 Apr 2025 12:00:13 +0900
From: Masami Hiramatsu (Google) <mhiramat@...nel.org>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: Mark Brown <broonie@...nel.org>, linux-kernel@...r.kernel.org,
 linux-trace-kernel@...r.kernel.org, bpf@...r.kernel.org, Masami Hiramatsu
 <mhiramat@...nel.org>, Mark Rutland <mark.rutland@....com>, Mathieu
 Desnoyers <mathieu.desnoyers@...icios.com>, Andrew Morton
 <akpm@...ux-foundation.org>, Sven Schnelle <svens@...ux.ibm.com>, Paul
 Walmsley <paul.walmsley@...ive.com>, Palmer Dabbelt <palmer@...belt.com>,
 Albert Ou <aou@...s.berkeley.edu>, Guo Ren <guoren@...nel.org>, Donglin
 Peng <dolinux.peng@...il.com>, Zheng Yejian <zhengyejian@...weicloud.com>,
 Aishwarya.TCV@....com
Subject: Re: [PATCH v4 2/4] ftrace: Add support for function argument to
 graph tracer

On Fri, 11 Apr 2025 15:26:10 -0400
Steven Rostedt <rostedt@...dmis.org> wrote:

> 
> 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.

Hi, I could find it. Let me reply!

> 
> If you want to see the original email:
> 
>   https://lore.kernel.org/all/20250411151358.1d4fd8c7@gandalf.local.home/
> 
> -- Steve
> 
> On Fri, 11 Apr 2025 15:13:58 -0400
> Steven Rostedt <rostedt@...dmis.org> wrote:
> 
> > On Fri, 11 Apr 2025 14:31:32 -0400
> > Steven Rostedt <rostedt@...dmis.org> 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
> 


-- 
Masami Hiramatsu (Google) <mhiramat@...nel.org>