[PATCH 2/2] perf ppc64le: Fix probe location when using DWARF

[Ravi Bangoria]

Powerpc has Global Entry Point and Local Entry Point for functions.
LEP catches call from both the GEP and the LEP. Symbol table of ELF
contains GEP and Offset from which we can calculate LEP, but debuginfo
does not have LEP info.

Currently, perf prioritize symbol table over dwarf to probe on LEP
for ppc64le. But when user tries to probe with function parameter,
we fall back to using dwarf(i.e. GEP) and when function called via
LEP, probe will never hit.

For example:
  $ objdump -d vmlinux
    ...
    do_sys_open():
    c0000000002eb4a0:       e8 00 4c 3c     addis   r2,r12,232
    c0000000002eb4a4:       60 00 42 38     addi    r2,r2,96
    c0000000002eb4a8:       a6 02 08 7c     mflr    r0
    c0000000002eb4ac:       d0 ff 41 fb     std     r26,-48(r1)

  $ sudo ./perf probe do_sys_open
  $ sudo cat /sys/kernel/debug/tracing/kprobe_events
    p:probe/do_sys_open _text+3060904

  $ sudo ./perf probe 'do_sys_open filename:string'
  $ sudo cat /sys/kernel/debug/tracing/kprobe_events
    p:probe/do_sys_open _text+3060896 filename_string=+0(%gpr4):string

For second case, perf probed on GEP. So when function will be called
via LEP, probe won't hit.

  $ sudo ./perf record -a -e probe:do_sys_open ls
    [ perf record: Woken up 1 times to write data ]
    [ perf record: Captured and wrote 0.195 MB perf.data ]

To resolve this issue, let's not prioritize symbol table, let perf
decide what it wants to use. Perf is already converting GEP to LEP
when it uses symbol table. When perf uses debuginfo, let it find
LEP offset form symbol table. This way we fall back to probe on LEP
for all cases.

After patch:
  $ sudo ./perf probe 'do_sys_open filename:string'
  $ sudo cat /sys/kernel/debug/tracing/kprobe_events
    p:probe/do_sys_open _text+3060904 filename_string=+0(%gpr4):string

  $ sudo ./perf record -a -e probe:do_sys_open ls
    [ perf record: Woken up 1 times to write data ]
    [ perf record: Captured and wrote 0.197 MB perf.data (11 samples) ]

Signed-off-by: Ravi Bangoria <ravi.bangoria@xxxxxxxxxxxxxxxxxx>
---
 tools/perf/arch/powerpc/util/sym-handling.c | 27 +++++++++++++++++----
 tools/perf/util/probe-event.c               | 37 ++++++++++++++++-------------
 tools/perf/util/probe-event.h               |  6 ++++-
 3 files changed, 49 insertions(+), 21 deletions(-)

diff --git a/tools/perf/arch/powerpc/util/sym-handling.c b/tools/perf/arch/powerpc/util/sym-handling.c
index c6d0f91..8d4dc97 100644
--- a/tools/perf/arch/powerpc/util/sym-handling.c
+++ b/tools/perf/arch/powerpc/util/sym-handling.c
@@ -54,10 +54,6 @@ int arch__compare_symbol_names(const char *namea, const char *nameb)
 #endif
 
 #if defined(_CALL_ELF) && _CALL_ELF == 2
-bool arch__prefers_symtab(void)
-{
-	return true;
-}
 
 #ifdef HAVE_LIBELF_SUPPORT
 void arch__sym_update(struct symbol *s, GElf_Sym *sym)
@@ -100,4 +96,27 @@ void arch__fix_tev_from_maps(struct perf_probe_event *pev,
 			tev->point.offset += lep_offset;
 	}
 }
+
+void arch__post_process_probe_trace_events(struct perf_probe_event *pev,
+					   int ntevs)
+{
+	struct probe_trace_event *tev;
+	struct map *map;
+	struct symbol *sym = NULL;
+	struct rb_node *tmp;
+	int i = 0;
+
+	map = get_target_map(pev->target, pev->uprobes);
+	if (!map || map__load(map, NULL) < 0)
+		return;
+
+	for (i = 0; i < ntevs; i++) {
+		tev = &pev->tevs[i];
+		map__for_each_symbol(map, sym, tmp) {
+			if (map->unmap_ip(map, sym->start) == tev->point.address)
+				arch__fix_tev_from_maps(pev, tev, map, sym);
+		}
+	}
+}
+
 #endif
diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
index 4e215e7..5efa535 100644
--- a/tools/perf/util/probe-event.c
+++ b/tools/perf/util/probe-event.c
@@ -178,7 +178,7 @@ static struct map *kernel_get_module_map(const char *module)
 	return NULL;
 }
 
-static struct map *get_target_map(const char *target, bool user)
+struct map *get_target_map(const char *target, bool user)
 {
 	/* Init maps of given executable or kernel */
 	if (user)
@@ -703,19 +703,32 @@ post_process_kernel_probe_trace_events(struct probe_trace_event *tevs,
 	return skipped;
 }
 
+void __weak
+arch__post_process_probe_trace_events(struct perf_probe_event *pev __maybe_unused,
+				      int ntevs __maybe_unused)
+{
+}
+
 /* Post processing the probe events */
-static int post_process_probe_trace_events(struct probe_trace_event *tevs,
+static int post_process_probe_trace_events(struct perf_probe_event *pev,
+					   struct probe_trace_event *tevs,
 					   int ntevs, const char *module,
 					   bool uprobe)
 {
-	if (uprobe)
-		return add_exec_to_probe_trace_events(tevs, ntevs, module);
+	int ret;
 
-	if (module)
+	if (uprobe)
+		ret = add_exec_to_probe_trace_events(tevs, ntevs, module);
+	else if (module)
 		/* Currently ref_reloc_sym based probe is not for drivers */
-		return add_module_to_probe_trace_events(tevs, ntevs, module);
+		ret = add_module_to_probe_trace_events(tevs, ntevs, module);
+	else
+		ret = post_process_kernel_probe_trace_events(tevs, ntevs);
 
-	return post_process_kernel_probe_trace_events(tevs, ntevs);
+	if (ret >= 0)
+		arch__post_process_probe_trace_events(pev, ntevs);
+
+	return ret;
 }
 
 /* Try to find perf_probe_event with debuginfo */
@@ -756,7 +769,7 @@ static int try_to_find_probe_trace_events(struct perf_probe_event *pev,
 
 	if (ntevs > 0) {	/* Succeeded to find trace events */
 		pr_debug("Found %d probe_trace_events.\n", ntevs);
-		ret = post_process_probe_trace_events(*tevs, ntevs,
+		ret = post_process_probe_trace_events(pev, *tevs, ntevs,
 						pev->target, pev->uprobes);
 		if (ret < 0 || ret == ntevs) {
 			clear_probe_trace_events(*tevs, ntevs);
@@ -2943,8 +2956,6 @@ errout:
 	return err;
 }
 
-bool __weak arch__prefers_symtab(void) { return false; }
-
 /* Concatinate two arrays */
 static void *memcat(void *a, size_t sz_a, void *b, size_t sz_b)
 {
@@ -3165,12 +3176,6 @@ static int convert_to_probe_trace_events(struct perf_probe_event *pev,
 	if (ret > 0 || pev->sdt)	/* SDT can be found only in the cache */
 		return ret == 0 ? -ENOENT : ret; /* Found in probe cache */
 
-	if (arch__prefers_symtab() && !perf_probe_event_need_dwarf(pev)) {
-		ret = find_probe_trace_events_from_map(pev, tevs);
-		if (ret > 0)
-			return ret; /* Found in symbol table */
-	}
-
 	/* Convert perf_probe_event with debuginfo */
 	ret = try_to_find_probe_trace_events(pev, tevs);
 	if (ret != 0)
diff --git a/tools/perf/util/probe-event.h b/tools/perf/util/probe-event.h
index e18ea9f..f4f45db 100644
--- a/tools/perf/util/probe-event.h
+++ b/tools/perf/util/probe-event.h
@@ -158,7 +158,6 @@ int show_line_range(struct line_range *lr, const char *module, bool user);
 int show_available_vars(struct perf_probe_event *pevs, int npevs,
 			struct strfilter *filter);
 int show_available_funcs(const char *module, struct strfilter *filter, bool user);
-bool arch__prefers_symtab(void);
 void arch__fix_tev_from_maps(struct perf_probe_event *pev,
 			     struct probe_trace_event *tev, struct map *map,
 			     struct symbol *sym);
@@ -173,4 +172,9 @@ int e_snprintf(char *str, size_t size, const char *format, ...)
 int copy_to_probe_trace_arg(struct probe_trace_arg *tvar,
 			    struct perf_probe_arg *pvar);
 
+struct map *get_target_map(const char *target, bool user);
+
+void arch__post_process_probe_trace_events(struct perf_probe_event *pev,
+					   int ntevs);
+
 #endif /*_PROBE_EVENT_H */
-- 
2.7.4