Re: [PATCH perf/core 3/3] perf-probe: Fix to probe on gcc generated functions in modules

[Arnaldo Carvalho de Melo <acme@kernel.org>]

Em Wed, Jan 04, 2017 at 12:31:39PM +0900, Masami Hiramatsu escreveu:
> Fix to probe on gcc generated functions on modules. Since
> probing on a module is based on its symbol name, it should
> be adjusted on actual symbols.
> 
> E.g. without this fix, perf probe shows probe definition
> on non-exist symbol as below.
>   -----
>   $ perf probe -m build-x86_64/net/netfilter/nf_nat.ko -F in_range*
>   in_range.isra.12
>   $ perf probe -m build-x86_64/net/netfilter/nf_nat.ko -D in_range
>   p:probe/in_range nf_nat:in_range+0
>   -----
> With this fix, perf probe correctly shows a probe on
> gcc-generated symbol.
>   -----
>   $ perf probe -m build-x86_64/net/netfilter/nf_nat.ko -D in_range
>   p:probe/in_range nf_nat:in_range.isra.12+0
>   -----

Tested this one on a x86-64 fedora25 system, applied all three.

As always, please take a look at the patch when sent to Ingo, I usually
put some committer notes there, in this case I put the test steps I
performed, using e1000e.ko and e1000_flash_cycle_ich8lan.constprop.22

BTW, it would be cool if...

Oops, I retract that, while I was testing what I was went to ask you to
implement, I saw that this last patch broke this use case:

[root@jouet ~]# perf probe -m e1000e e1000_xmit_frame
Failed to get ELF symbols for e1000e
Probe point 'e1000_xmit_frame' not found.
  Error: Failed to add events.
[root@jouet ~]#

If I remove it, I get it back:

[root@jouet ~]# perf probe -m e1000e e1000_xmit_frame
Added new event:
  probe:e1000_xmit_frame (on e1000_xmit_frame in e1000e)

You can now use it in all perf tools, such as:

	perf record -e probe:e1000_xmit_frame -aR sleep 1

[root@jouet ~]# perf probe -l
  probe:e1000_xmit_frame (on e1000_get_link_up_info_80003es2lan:7@intel/e1000e/80003es2lan.c in e1000e)
[root@jouet ~]#

BTW, what I would find cool, besides fixing this new problem, would be that:

  perf probe e1000_xmit_frame

worked, as we can get the module name from kallsyms:

[acme@jouet linux]$ grep e1000_xmit_frame /proc/kallsyms 
ffffffffc046fc10 t e1000_xmit_frame	[e1000e]
[acme@jouet linux]$ 

I applied the first two patches, and now I'm preparing a pull req to Ingo,

Thanks!

- Arnaldo
 
> Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
> ---
>  tools/perf/util/probe-event.c  |   38 +++++++++++++++++++++++---------------
>  tools/perf/util/probe-finder.c |    2 +-
>  tools/perf/util/probe-finder.h |    2 ++
>  3 files changed, 26 insertions(+), 16 deletions(-)
> 
> diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
> index 4a57c8a..f75c99a 100644
> --- a/tools/perf/util/probe-event.c
> +++ b/tools/perf/util/probe-event.c
> @@ -682,15 +682,19 @@ static int add_exec_to_probe_trace_events(struct probe_trace_event *tevs,
>  	return ret;
>  }
>  
> -static int add_module_to_probe_trace_events(struct probe_trace_event *tevs,
> -					    int ntevs, const char *module)
> +static int
> +post_process_module_probe_trace_events(struct probe_trace_event *tevs,
> +				       int ntevs, const char *module,
> +				       struct debuginfo *dinfo)
>  {
> +	Dwarf_Addr text_offs;
>  	int i, ret = 0;
>  	char *mod_name = NULL;
>  
>  	if (!module)
>  		return 0;
>  
> +	debuginfo__get_text_offset(dinfo, &text_offs);
>  	mod_name = find_module_name(module);
>  
>  	for (i = 0; i < ntevs; i++) {
> @@ -700,9 +704,15 @@ static int add_module_to_probe_trace_events(struct probe_trace_event *tevs,
>  			ret = -ENOMEM;
>  			break;
>  		}
> +		/* kernel module needs a special care to adjust addresses */
> +		tevs[i].point.address -= (unsigned long)text_offs;
>  	}
>  
>  	free(mod_name);
> +
> +	if (!ret)
> +		ret = post_process_offline_probe_trace_events(tevs, ntevs,
> +								module);
>  	return ret;
>  }
>  
> @@ -760,7 +770,7 @@ arch__post_process_probe_trace_events(struct perf_probe_event *pev __maybe_unuse
>  static int post_process_probe_trace_events(struct perf_probe_event *pev,
>  					   struct probe_trace_event *tevs,
>  					   int ntevs, const char *module,
> -					   bool uprobe)
> +					   bool uprobe, struct debuginfo *dinfo)
>  {
>  	int ret;
>  
> @@ -768,7 +778,8 @@ static int post_process_probe_trace_events(struct perf_probe_event *pev,
>  		ret = add_exec_to_probe_trace_events(tevs, ntevs, module);
>  	else if (module)
>  		/* Currently ref_reloc_sym based probe is not for drivers */
> -		ret = add_module_to_probe_trace_events(tevs, ntevs, module);
> +		ret = post_process_module_probe_trace_events(tevs, ntevs,
> +							     module, dinfo);
>  	else
>  		ret = post_process_kernel_probe_trace_events(tevs, ntevs);
>  
> @@ -812,30 +823,27 @@ static int try_to_find_probe_trace_events(struct perf_probe_event *pev,
>  		}
>  	}
>  
> -	debuginfo__delete(dinfo);
> -
>  	if (ntevs > 0) {	/* Succeeded to find trace events */
>  		pr_debug("Found %d probe_trace_events.\n", ntevs);
>  		ret = post_process_probe_trace_events(pev, *tevs, ntevs,
> -						pev->target, pev->uprobes);
> +					pev->target, pev->uprobes, dinfo);
>  		if (ret < 0 || ret == ntevs) {
> +			pr_debug("Post processing failed or all events are skipped. (%d)\n", ret);
>  			clear_probe_trace_events(*tevs, ntevs);
>  			zfree(tevs);
> +			ntevs = 0;
>  		}
> -		if (ret != ntevs)
> -			return ret < 0 ? ret : ntevs;
> -		ntevs = 0;
> -		/* Fall through */
>  	}
>  
> +	debuginfo__delete(dinfo);
> +
>  	if (ntevs == 0)	{	/* No error but failed to find probe point. */
>  		pr_warning("Probe point '%s' not found.\n",
>  			   synthesize_perf_probe_point(&pev->point));
>  		return -ENOENT;
> -	}
> -	/* Error path : ntevs < 0 */
> -	pr_debug("An error occurred in debuginfo analysis (%d).\n", ntevs);
> -	if (ntevs < 0) {
> +	} else if (ntevs < 0) {
> +		/* Error path : ntevs < 0 */
> +		pr_debug("An error occurred in debuginfo analysis (%d).\n", ntevs);
>  		if (ntevs == -EBADF)
>  			pr_warning("Warning: No dwarf info found in the vmlinux - "
>  				"please rebuild kernel with CONFIG_DEBUG_INFO=y.\n");
> diff --git a/tools/perf/util/probe-finder.c b/tools/perf/util/probe-finder.c
> index df4debe..6dede24 100644
> --- a/tools/perf/util/probe-finder.c
> +++ b/tools/perf/util/probe-finder.c
> @@ -1501,7 +1501,7 @@ int debuginfo__find_available_vars_at(struct debuginfo *dbg,
>  }
>  
>  /* For the kernel module, we need a special code to get a DIE */
> -static int debuginfo__get_text_offset(struct debuginfo *dbg, Dwarf_Addr *offs)
> +int debuginfo__get_text_offset(struct debuginfo *dbg, Dwarf_Addr *offs)
>  {
>  	int n, i;
>  	Elf32_Word shndx;
> diff --git a/tools/perf/util/probe-finder.h b/tools/perf/util/probe-finder.h
> index f1d8558..1e03bbb 100644
> --- a/tools/perf/util/probe-finder.h
> +++ b/tools/perf/util/probe-finder.h
> @@ -46,6 +46,8 @@ int debuginfo__find_trace_events(struct debuginfo *dbg,
>  int debuginfo__find_probe_point(struct debuginfo *dbg, unsigned long addr,
>  				struct perf_probe_point *ppt);
>  
> +int debuginfo__get_text_offset(struct debuginfo *dbg, Dwarf_Addr *offs);
> +
>  /* Find a line range */
>  int debuginfo__find_line_range(struct debuginfo *dbg, struct line_range *lr);
>