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SubjectRe: [RFC PATCH] perf tools: allow map files to specify DSO
Em Tue, Apr 24, 2018 at 02:49:09PM -0400, Josh Hunt escreveu:
> Add the ability to specify a DSO in the /tmp/perf-<PID>.map file.
> The DSO should be the first line in the file and readable by the
> running user. If a valid DSO is found all other contents of the
> file will be ignored. This allows things like callchain unwinding
> with DWARF to work.

Pekka, Andi, Stephane, do you guys see any problems with this?

If this flies, tools/perf/Documentation/jit-interface.txt needs
updating.

- Arnaldo

> Suggested-by: Wang Nan <wangnan0@huawei.com>
> Signed-off-by: Josh Hunt <johunt@akamai.com>
>
> ---
> We have an application which uses huge pages for its text section, but
> still needs the ability to do callchain unwinding with DWARF. We use
> the perf-<PID>.map file setup to do symbol resolution and that works
> great, but callchain unwinding fails.
>
> A few months ago I mentioned this to Wang Nan and he suggested a way
> around this problem could be to specify the path of the DSO in the map
> file. The attached patch is my initial hack at this. Running with this
> patch I can now get full callchain unwinding with DWARF.
>
> FWIW LBR + map file works with callchains, but unfortunately there are
> some cases where we still need DWARF.
>
> I was hoping to get feedback on whether this is the right way to solve
> this problem, and if not what should I do to get this working? If the
> idea is OK I will clean this up and resubmit an official patch. Current
> patch is against 4.14 stable.
>
> Thanks!
> ---
> tools/perf/util/map.c | 32 ++++++++++++++++++++++++++++++++
> 1 file changed, 32 insertions(+)
>
> diff --git a/tools/perf/util/map.c b/tools/perf/util/map.c
> index 4e7bd2750122..98d6af2c854d 100644
> --- a/tools/perf/util/map.c
> +++ b/tools/perf/util/map.c
> @@ -143,12 +143,37 @@ void map__init(struct map *map, enum map_type type,
> RB_CLEAR_NODE(&map->rb_node);
> map->groups = NULL;
> map->erange_warned = false;
> refcount_set(&map->refcnt, 1);
> }
>
> +static bool replace_anon(char *mapfilename)
> +{
> + FILE *file = NULL;
> + bool ret = false;
> +
> + file = fopen(mapfilename, "r");
> + if (file != NULL) {
> + char *line;
> + size_t line_len, linesz=0;
> +
> + line_len = getline(&line, &linesz, file);
> + if (line_len > 0) {
> + line[--line_len] = '\0';
> + if (!access(line, R_OK)) {
> + strlcpy(mapfilename, line, line_len+1);
> + ret = true;
> + }
> + free(line);
> + }
> + fclose(file);
> + }
> +
> + return ret;
> +}
> +
> struct map *map__new(struct machine *machine, u64 start, u64 len,
> u64 pgoff, u32 d_maj, u32 d_min, u64 ino,
> u64 ino_gen, u32 prot, u32 flags, char *filename,
> enum map_type type, struct thread *thread)
> {
> struct map *map = malloc(sizeof(*map));
> @@ -174,12 +199,19 @@ struct map *map__new(struct machine *machine, u64 start, u64 len,
> nsi = nsinfo__get(thread->nsinfo);
>
> if ((anon || no_dso) && nsi && type == MAP__FUNCTION) {
> snprintf(newfilename, sizeof(newfilename),
> "/tmp/perf-%d.map", nsi->pid);
> filename = newfilename;
> + /*
> + * Check to see if map file references DSO to use, if so, use it.
> + */
> + if (anon && replace_anon(newfilename)) {
> + anon = 0;
> + filename = newfilename;
> + }
> }
>
> if (android) {
> if (replace_android_lib(filename, newfilename))
> filename = newfilename;
> }
> --
> 1.9.1

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