Message-ID: <20250411151358.1d4fd8c7@gandalf.local.home>
Date: Fri, 11 Apr 2025 15:13:58 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Mark Brown <broonie@...nel.org>
Cc: 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 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 $TEST_STRING
p vfs_read \1 \2 \3 \4 \5 \6 \7 \8 \9 \10 \11 \12 \13 \14 \15 \16 \17 \18 \19 \20 \21 \22 \23 \24 \25 \26 \27 \28 \29 \30 \31 \32 \33 \34 \35 \36 \37 \38 \39 \40 \41 \42 \43 \44 \45 \46 \47 \48 \49 \50 \51 \52 \53 \54 \55 \56 \57 \58 \59 \60 \61 \62 \63 \64 \65 \66 \67 \68 \69 \70 \71 \72 \73 \74 \75 \76 \77 \78 \79 \80 \81 \82 \83 \84 \85 \86 \87 \88 \89 \90 \91 \92 \93 \94 \95 \96 \97 \98 \99 \100 \101 \102 \103 \104 \105 \106 \107 \108 \109 \110 \111 \112 \113 \114 \115 \116 \117 \118 \119 \120 \121 \122 \123 \124 \125 \126 \127 \128
# echo "$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 arg2=\2 arg3=\3 arg4=\4 arg5=\5 arg6=\6 arg7=\7 arg8=\8 arg9=\9 arg10=\10 arg11=\11 arg12=\12 arg13=\13 arg14=\14 arg15=\15 arg16=\16 arg17=\17 arg18=\18 arg19=\19 arg20=\20 arg21=\21 arg22=\22 arg23=\23 arg24=\24 arg25=\25 arg26=\26 arg27=\27 arg28=\28 arg29=\29 arg30=\30 arg31=\31 arg32=\32 arg33=\33 arg34=\34 arg35=\35 arg36=\36 arg37=\37 arg38=\38 arg39=\39 arg40=\40 arg41=\41 arg42=\42 arg43=\43 arg44=\44 arg45=\45 arg46=\46 arg47=\47 arg48=\48 arg49=\49 arg50=\50 arg51=\51 arg52=\52 arg53=\53 arg54=\54 arg55=\55 arg56=\56 arg57=\57 arg58=\58 arg59=\59 arg60=\60 arg61=\61 arg62=\62 arg63=\63 arg64=\64 arg65=\65 arg66=\66 arg67=\67 arg68=\68 arg69=\69 arg70=\70 arg71=\71 arg72=\72 arg73=\73 arg74=\74 arg75=\75 arg76=\76 arg77=\77 arg78=\78 arg79=\79 arg80=\80 arg81=\81 arg82=\82 arg83=\83 arg84=\84 arg85=\85 arg86=\86 arg87=\87 arg88=\88 arg89=\89 arg90=\90 arg91=\91 arg92=\92 arg93=\93 arg94=\94 arg95=\95 arg96=\96 arg97=\97 arg98=\98 arg99=\99 arg100=\100 arg101=\101 arg102=\102 arg103=\103 arg104=\104 arg105=\105 arg106=\106 arg107=\107 arg108=\108 arg109=\109 arg110=\110 arg111=\111 arg112=\112 arg113=\113 arg114=\114 arg115=\115 arg116=\116 arg117=\117 arg118=\118 arg119=\119 arg120=\120 arg121=\121 arg122=\122 arg123=\123 arg124=\124 arg125=\125 arg126=\126 arg127=\127 arg128=\128
-------------------------->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 	 
 
  
   8 9         8 9   ␦  9   ! " # $ % & ' 8 9 ( ) * + , - . / 8 9 0 1 2 3 4 5 6 7 8 9 8 9 : ; < = > ? 8 9 \80 \81 \82 \83 \84 \85 \86 \87 \88 \89 \90 \91 \92 \93 \94 \95 \96 \97 \98 \99 @ A B C D E F G89 H I J K L M N O 	8 	9 P Q R S T U V W 
8
# 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

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