linux-kernel - [PATCH v4 3/3] perf: powerpc: choose local entry point with kretprobes

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Message-Id: <9de477aa0064e0a066146be5b3629615b8957960.1488475783.git.naveen.n.rao@linux.vnet.ibm.com>
Date:   Thu,  2 Mar 2017 23:25:07 +0530
From:   "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org,
        Ananth N Mavinakayanahalli <ananth@...ux.vnet.ibm.com>,
        Michael Ellerman <mpe@...erman.id.au>
Subject: [PATCH v4 3/3] perf: powerpc: choose local entry point with kretprobes

perf now uses an offset from _text/_stext for kretprobes if the kernel
supports it, rather than the actual function name. As such, let's choose
the LEP for powerpc ABIv2 so as to ensure the probe gets hit. Do it only
if the kernel supports specifying offsets with kretprobes.

Signed-off-by: Naveen N. Rao <naveen.n.rao@...ux.vnet.ibm.com>
---
 tools/perf/arch/powerpc/util/sym-handling.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/tools/perf/arch/powerpc/util/sym-handling.c b/tools/perf/arch/powerpc/util/sym-handling.c
index 1030a6e504bb..cc7c2697c036 100644
--- a/tools/perf/arch/powerpc/util/sym-handling.c
+++ b/tools/perf/arch/powerpc/util/sym-handling.c
@@ -10,6 +10,7 @@
 #include "symbol.h"
 #include "map.h"
 #include "probe-event.h"
+#include "probe-file.h"
 
 #ifdef HAVE_LIBELF_SUPPORT
 bool elf__needs_adjust_symbols(GElf_Ehdr ehdr)
@@ -79,11 +80,12 @@ void arch__fix_tev_from_maps(struct perf_probe_event *pev,
 	 * However, if the user specifies an offset, we fall back to using the
 	 * GEP since all userspace applications (objdump/readelf) show function
 	 * disassembly with offsets from the GEP.
-	 *
-	 * In addition, we shouldn't specify an offset for kretprobes.
 	 */
-	if (pev->point.offset || (!pev->uprobes && pev->point.retprobe) ||
-	    !map || !sym)
+	if (pev->point.offset || !map || !sym)
+		return;
+
+	/* For kretprobes, add an offset only if the kernel supports it */
+	if (!pev->uprobes && pev->point.retprobe && !kretprobe_offset_is_supported())
 		return;
 
 	lep_offset = PPC64_LOCAL_ENTRY_OFFSET(sym->arch_sym);
-- 
2.11.1