linux-kernel - [PATCH] perf uretprobe ppc64le: Fix probe location

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Message-Id: <1475576865-6562-1-git-send-email-ravi.bangoria@linux.vnet.ibm.com>
Date:   Tue,  4 Oct 2016 15:57:45 +0530
From:   Ravi Bangoria <ravi.bangoria@...ux.vnet.ibm.com>
To:     linux-kernel@...r.kernel.org, acme@...nel.org
Cc:     peterz@...radead.org, mingo@...hat.com,
        alexander.shishkin@...ux.intel.com,
        naveen.n.rao@...ux.vnet.ibm.com, bsingharora@...il.com,
        mhiramat@...nel.org,
        Ravi Bangoria <ravi.bangoria@...ux.vnet.ibm.com>
Subject: [PATCH] perf uretprobe ppc64le: Fix probe location

Perf uretprobe probes on GEP(Glabal Entry Point) which fails to record
all function calls via LEP(Local Entry Point). Fix that by probing on LEP.

Objdump:
  00000000100005f0 <doit>:
      100005f0:   02 10 40 3c     lis     r2,4098
      100005f4:   00 7f 42 38     addi    r2,r2,32512
      100005f8:   a6 02 08 7c     mflr    r0
      100005fc:   10 00 01 f8     std     r0,16(r1)
      10000600:   f8 ff e1 fb     std     r31,-8(r1)

Before applying patch:
  $ cat /sys/kernel/debug/tracing/uprobe_events
    r:probe_uprobe_test/doit /home/ravi/uprobe_test:0x00000000000005f0

After applying patch:
  $ cat /sys/kernel/debug/tracing/uprobe_events
    r:probe_uprobe_test/doit /home/ravi/uprobe_test:0x00000000000005f8

This is not the case with kretprobe because kernel itself finds LEP
and probes on it.

Signed-off-by: Ravi Bangoria <ravi.bangoria@...ux.vnet.ibm.com>
---
 tools/perf/arch/powerpc/util/sym-handling.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/tools/perf/arch/powerpc/util/sym-handling.c b/tools/perf/arch/powerpc/util/sym-handling.c
index ed9d5d1..1030a6e 100644
--- a/tools/perf/arch/powerpc/util/sym-handling.c
+++ b/tools/perf/arch/powerpc/util/sym-handling.c
@@ -82,7 +82,8 @@ void arch__fix_tev_from_maps(struct perf_probe_event *pev,
 	 *
 	 * In addition, we shouldn't specify an offset for kretprobes.
 	 */
-	if (pev->point.offset || pev->point.retprobe || !map || !sym)
+	if (pev->point.offset || (!pev->uprobes && pev->point.retprobe) ||
+	    !map || !sym)
 		return;
 
 	lep_offset = PPC64_LOCAL_ENTRY_OFFSET(sym->arch_sym);
-- 
2.7.4