perf probe ppc64le: Fix probe location when using DWARF

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 <[e-mail]>
Acked-by: Masami Hiramatsu <[e-mail]>
Cc: Alexander Shishkin <[e-mail]>
Cc: Ananth N Mavinakayanahalli <[e-mail]>
Cc: Balbir Singh <[e-mail]>
Cc: Namhyung Kim <[e-mail]>
Cc: Naveen N. Rao <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Wang Nan <[e-mail]>
Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/perf/arch/powerpc/util/sym-handling.c

···
 #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)
···
 			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

tools/perf/util/probe-event.c

···
 	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)
···
 	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)
 {
+	int ret;
+
 	if (uprobe)
-		return add_exec_to_probe_trace_events(tevs, ntevs, module);
-
-	if (module)
+		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 */
···
 
 	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);
···
 	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)
 {
···
 	ret = find_probe_trace_events_from_cache(pev, tevs);
 	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);

tools/perf/util/probe-event.h

···
 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);
···
 
 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 */