linux-kernel - Re: [PATCH v2] perf/probe: Change MAX

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Date:   Tue, 21 Mar 2017 14:19:50 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Ravi Bangoria <ravi.bangoria@...ux.vnet.ibm.com>
Cc:     acme@...hat.com, linux-kernel@...r.kernel.org,
        alexis.berlemont@...il.com, peterz@...radead.org, mingo@...hat.com,
        alexander.shishkin@...ux.intel.com, mpe@...erman.id.au,
        naveen.n.rao@...ux.vnet.ibm.com, maddy@...ux.vnet.ibm.com
Subject: Re: [PATCH v2] perf/probe: Change MAX_CMDLEN

On Tue,  7 Feb 2017 11:15:47 +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 upto 4094 characters(4096 - 2 (\n\0)), increase value
> of MAX_CMDLEN to 4094.

This looks good to me.

Acked-by: Masami Hiramatsu <mhiramat@...nel.org>

Thanks,

> 
> Signed-off-by: Ravi Bangoria <ravi.bangoria@...ux.vnet.ibm.com>
> ---
> Changes in v2:
>   - Set MAX_CMDLEN to 4094 instead of 512
> 
>  tools/perf/util/probe-event.c | 1 -
>  tools/perf/util/probe-file.c  | 3 ++-
>  2 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
> index 6a6f44d..e6e3244 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..fdabe7e 100644
> --- a/tools/perf/util/probe-file.c
> +++ b/tools/perf/util/probe-file.c
> @@ -29,7 +29,8 @@
>  #include "session.h"
>  #include "perf_regs.h"
>  
> -#define MAX_CMDLEN 256
> +/* 4096 - 2 ('\n' + '\0') */
> +#define MAX_CMDLEN 4094
>  
>  static void print_open_warning(int err, bool uprobe)
>  {
> -- 
> 2.9.3
> 


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