Re: [PATCH 2/2] perf ppc64le: Fix probe location when using DWARF
From: Masami Hiramatsu
Date: Tue Aug 09 2016 - 10:02:54 EST
On Tue, 9 Aug 2016 01:23:25 -0500
Ravi Bangoria <ravi.bangoria@xxxxxxxxxxxxxxxxxx> wrote:
> 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) ]
OK, I see.
And I'd like to add note below.
This reverts commit d5c2e2c17ae1 ("perf probe ppc64le: Prefer symbol
table lookup over DWARF").
Acked-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
for this series.
Thanks,
>
> 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
>
--
Masami Hiramatsu <mhiramat@xxxxxxxxxx>