[PATCH 17/19] perf powerpc: Choose local entry point with kretprobes

[Arnaldo Carvalho de Melo]

From: "Naveen N. Rao" <naveen.n.rao at linux.vnet.ibm.com>

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 at linux.vnet.ibm.com>
Acked-by: Masami Hiramatsu <mhiramat at kernel.org>
Cc: Ananth N Mavinakayanahalli <ananth at linux.vnet.ibm.com>
Cc: Michael Ellerman <mpe at ellerman.id.au>
Cc: Steven Rostedt <rostedt at goodmis.org>
Cc: linuxppc-dev at lists.ozlabs.org
Link: http://lkml.kernel.org/r/7445b5334673ef5404ac1d12609bad4d73d2b567.1488961018.git.naveen.n.rao@linux.vnet.ibm.com
Signed-off-by: Arnaldo Carvalho de Melo <acme at redhat.com>
---
 tools/perf/arch/powerpc/util/sym-handling.c | 14 ++++++++++----
 1 file changed, 10 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..39dbe512b9fc 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)
@@ -79,13 +80,18 @@ 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) {
+#ifdef HAVE_LIBELF_SUPPORT
+		if (!kretprobe_offset_is_supported())
+#endif
+			return;
+	}
+
 	lep_offset = PPC64_LOCAL_ENTRY_OFFSET(sym->arch_sym);
 
 	if (map->dso->symtab_type == DSO_BINARY_TYPE__KALLSYMS)
-- 
2.9.3