[PATCH 4/6] perf annotate: fix it for non-prelinked *.so

Kirill Smelkov
2010-01-08T12:50:33Z

The problem was we were incorrectly calculating objdump addresses for
sym->start and sym->end, look:

For simple ET_DYN type DSO (*.so) with one function, objdump -dS output
is something like this:

000004ac <my_strlen>:
int my_strlen(const char *s)
4ac: 55 push %ebp
4ad: 89 e5 mov %esp,%ebp
4af: 83 ec 10 sub $0x10,%esp
{

i.e. we have relative-to-dso-mapping IPs (=RIP) there.

For ET_EXEC type and probably for prelinked libs as well (sorry can't
test - I don't use prelink) objdump outputs absolute IPs, e.g.

08048604 <zz_strlen>:
extern "C"
int zz_strlen(const char *s)
8048604: 55 push %ebp
8048605: 89 e5 mov %esp,%ebp
8048607: 83 ec 10 sub $0x10,%esp
{

So, if sym->start is always relative to dso mapping(*), we'll have to
unmap it for ET_EXEC like cases, and leave as is for ET_DYN cases.

(*) and it is - we've explicitely made it relative. Look for
adjust_symbols handling in dso__load_sym()

Previously we were always unmapping sym->start and for ET_DYN dsos
resulting addresses were wrong, and so objdump output was empty.

The end result was that perf annotate output for symbols from
non-prelinked *.so had always 0.00% percents only, which is wrong.

----

To fix it, let's introduce a helper for converting rip to objdump
address, and also let's document what map_ip() and unmap_ip() do -- I
had to study sources for several hours to understand it.

Signed-off-by: Kirill Smelkov <kirr@landau.phys.spbu.ru>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Mike Galbraith <efault@gmx.de>
---
tools/perf/builtin-annotate.c | 4 ++--
tools/perf/util/map.c | 14 ++++++++++++++
tools/perf/util/map.h | 9 +++++++++
3 files changed, 25 insertions(+), 2 deletions(-)

diff --git a/tools/perf/builtin-annotate.c b/tools/perf/builtin-annotate.c
index 117bbae..117301a 100644
--- a/tools/perf/builtin-annotate.c
+++ b/tools/perf/builtin-annotate.c
@@ -195,7 +195,7 @@ static int parse_line(FILE *file, struct hist_entry *he, u64 len)
line_ip = -1;
}

- start = he->map->unmap_ip(he->map, sym->start);
+ start = map__rip_2objdump(he->map, sym->start);

if (line_ip != -1) {
const char *path = NULL;
@@ -405,7 +405,7 @@ static void annotate_sym(struct hist_entry *he)
dso, dso->long_name, sym, sym->name);

sprintf(command, "objdump --start-address=0x%016Lx --stop-address=0x%016Lx -dS %s|grep -v %s",
- map->unmap_ip(map, sym->start), map->unmap_ip(map, sym->end),
+ map__rip_2objdump(map, sym->start), map__rip_2objdump(map, sym->end),
filename, filename);

if (verbose >= 3)
diff --git a/tools/perf/util/map.c b/tools/perf/util/map.c
index c4d55a0..d6da969 100644
--- a/tools/perf/util/map.c
+++ b/tools/perf/util/map.c
@@ -201,3 +201,17 @@ size_t map__fprintf(struct map *self, FILE *fp)
return fprintf(fp, " %Lx-%Lx %Lx %s\n",
self->start, self->end, self->pgoff, self->dso->name);
}
+
+
+
+/*
+ * objdump wants/reports absolute IPs for ET_EXEC, and RIPs for ET_DYN.
+ * map->dso->adjust_symbols==1 for ET_EXEC-like cases.
+ */
+u64 map__rip_2objdump(struct map *map, u64 rip)
+{
+ u64 addr = map->dso->adjust_symbols ?
+ map->unmap_ip(map, rip) : /* RIP -> IP */
+ rip;
+ return addr;
+}
diff --git a/tools/perf/util/map.h b/tools/perf/util/map.h
index 72f0b6a..39fa478 100644
--- a/tools/perf/util/map.h
+++ b/tools/perf/util/map.h
@@ -24,8 +24,12 @@ struct map {
u64 end;
enum map_type type;
u64 pgoff;
+
+ /* ip -> dso rip */
u64 (*map_ip)(struct map *, u64);
+ /* dso rip -> ip */
u64 (*unmap_ip)(struct map *, u64);
+
struct dso *dso;
};

@@ -44,6 +48,11 @@ static inline u64 identity__map_ip(struct map *map __used, u64 ip)
return ip;
}

+
+/* rip -> addr suitable for passing to `objdump --start-address=` */
+u64 map__rip_2objdump(struct map *map, u64 rip);
+
+
struct symbol;
struct mmap_event;

--
1.6.6.79.gd514e.dirty