linux-kernel - Re: [PATCH 5/5] perf/probe: Change MAX

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Message-Id: <20170207104041.aebc2eb9ad4a6dd01f8a0f5c@kernel.org>
Date:   Tue, 7 Feb 2017 10:40:41 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Ravi Bangoria <ravi.bangoria@...ux.vnet.ibm.com>
Cc:     acme@...hat.com, alexis.berlemont@...il.com,
        linux-kernel@...r.kernel.org, peterz@...radead.org,
        mingo@...hat.com, alexander.shishkin@...ux.intel.com,
        mpe@...erman.id.au, naveen.n.rao@...ux.vnet.ibm.com,
        mhiramat@...nel.org, maddy@...ux.vnet.ibm.com
Subject: Re: [PATCH 5/5] perf/probe: Change MAX_CMDLEN

On Thu,  2 Feb 2017 16:41:43 +0530
Ravi Bangoria <ravi.bangoria@...ux.vnet.ibm.com> wrote:

> There are many SDT markers in powerpc whose uprobe definition goes
> beyond current MAX_CMDLEN, especially when target filename is long
> and sdt marker has long list of arguments. For example, definition
> of sdt marker
> 
>   method__compile__end: 8@17 8@9 8@10 -4@8 8@7 -4@6 8@5 -4@4 1@37(28)
> 
> from file
> 
>   /usr/lib/jvm/java-1.8.0-openjdk-1.8.0.91-2.b14.fc22.ppc64/jre/lib/\
>      ppc64/server/libjvm.so
> 
> is
> 
>   p:sdt_hotspot/method__compile__end /usr/lib/jvm/java-1.8.0-openjdk-\
>     1.8.0.91-2.b14.fc22.ppc64/jre/lib/ppc64/server/libjvm.so:0x4c4e00\
>     arg1=%gpr17:u64 arg2=%gpr9:u64 arg3=%gpr10:u64 arg4=%gpr8:s32\
>     arg5=%gpr7:u64 arg6=%gpr6:s32 arg7=%gpr5:u64 arg8=%gpr4:s32\
>     arg9=+37(%gpr28):u8
> 
> Perf probe fails with seg fault for such markers. As uprobe_events file
> accepts definition beyond 256 characters, increase value of MAX_CMDLEN
> to 512.

OK, actually in the kernel side, it accepts up to 4094 (+"\n\0")
so it is a good time to expand it to 4094.
(I found another buggy message in kernel... will be fixed soon)

Thank you,

> Signed-off-by: Ravi Bangoria <ravi.bangoria@...ux.vnet.ibm.com>
> ---
>  tools/perf/util/probe-event.c | 1 -
>  tools/perf/util/probe-file.c  | 2 +-
>  2 files changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
> index 2c1bca2..5f3256f 100644
> --- a/tools/perf/util/probe-event.c
> +++ b/tools/perf/util/probe-event.c
> @@ -47,7 +47,6 @@
>  #include "probe-file.h"
>  #include "session.h"
>  
> -#define MAX_CMDLEN 256
>  #define PERFPROBE_GROUP "probe"
>  
>  bool probe_event_dry_run;	/* Dry run flag */
> diff --git a/tools/perf/util/probe-file.c b/tools/perf/util/probe-file.c
> index 38eca3c..1580e26 100644
> --- a/tools/perf/util/probe-file.c
> +++ b/tools/perf/util/probe-file.c
> @@ -29,7 +29,7 @@
>  #include "session.h"
>  #include "perf_regs.h"
>  
> -#define MAX_CMDLEN 256
> +#define MAX_CMDLEN 512
>  
>  static void print_open_warning(int err, bool uprobe)
>  {
> -- 
> 2.9.3
> 


-- 
Masami Hiramatsu <mhiramat@...nel.org>