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

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Date:   Tue,  7 Feb 2017 11:15:47 +0530
From:   Ravi Bangoria <ravi.bangoria@...ux.vnet.ibm.com>
To:     acme@...hat.com, linux-kernel@...r.kernel.org, mhiramat@...nel.org
Cc:     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,
        Ravi Bangoria <ravi.bangoria@...ux.vnet.ibm.com>
Subject: [PATCH v2] perf/probe: Change MAX_CMDLEN

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.

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