linux-kernel - Re: [PATCH] perf probe: Fix module probing with shortname

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Date:	Wed, 23 Sep 2015 22:50:08 -0300
From:	Arnaldo Carvalho de Melo <acme@...nel.org>
To:	"Wangnan (F)" <wangnan0@...wei.com>
Cc:	linux-kernel@...r.kernel.org, lizefan@...wei.com, pi3orama@....com,
	Namhyung Kim <namhyung@...nel.org>,
	Jiri Olsa <jolsa@...hat.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
Subject: Re: [PATCH] perf probe: Fix module probing with shortname

Em Wed, Sep 23, 2015 at 01:03:19PM -0300, Arnaldo Carvalho de Melo escreveu:
> Em Tue, Sep 22, 2015 at 11:49:02PM -0300, Arnaldo Carvalho de Melo escreveu:
> > Em Wed, Sep 23, 2015 at 09:14:44AM +0800, Wangnan (F) escreveu:
> > > On 2015/9/22 21:35, Arnaldo Carvalho de Melo wrote:
> > > >Em Tue, Sep 22, 2015 at 03:34:32AM +0000, Wang Nan escreveu:
> > > >>This is caused by a misunderstood of dso->kernel in kernel_get_module_dso()
> > > >>that, for kernel module, dso->kernel is DSO_TYPE_USER. dso->kernel is DSO_TYPE_KERNEL
> > > >>iff dso is vmlinux.
> > > >Kernel modules having DSO_TYPE_USER seems to be the bug, no? I'll try to
> > > >check that...

> > > I also noticed this problem when I working on commit
> > > 1f121b03d058dd07199d8924373d3c52a207f63b ("perf tools: Deal with
> > > kernel module names in '[]' correctly") ;)

> > Thanks for working on this, it is an area that needs cleaning up, too
> > many ways to say what a dso is, will study your findings and try to come
> > up with a patch proposal tomorrow.
> > > So care must be taken.
> 
> So, yes, there are multiple uses for this dso->kernel thing, we need to
> look at each one and go on clarifying it so that this gets corrected and
> sane, but I think we need some helpers to clarify all this, namely:
> 
> 	Adding DSO_TYPE_KMODULE and DSO_TYPE_GUEST_KMODULE, setting
> dso->kernel with it when loading host and guest kernel modules and
> adding:
> 
> 	bool dso__is_host_kernel(struct dso *dso)
> 	bool dso__is_host_kmodule(struct dso *dso)
> 
> 	bool dso__is_guest_kernel(struct dso *dso)

So I tried this, ended up basically using __map__is_kernel(), in several
places, which I think is right, and I've stashed in my tmp.perf/core
branch so that you can take a look.

But then I realized that we already have a better way to achieve what is
needed in that function, see the patch below, fixed things for me:

diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
index 2b78e8f19b45..7fb0533ab18c 100644
--- a/tools/perf/util/probe-event.c
+++ b/tools/perf/util/probe-event.c
@@ -269,12 +269,13 @@ static int kernel_get_module_dso(const char *module, struct dso **pdso)
 	int ret = 0;
 
 	if (module) {
-		list_for_each_entry(dso, &host_machine->dsos.head, node) {
-			if (!dso->kernel)
-				continue;
-			if (strncmp(dso->short_name + 1, module,
-				    dso->short_name_len - 2) == 0)
-				goto found;
+		char module_name[128];
+
+		snprintf(module_name, sizeof(module_name), "[%s]", module);
+		map = map_groups__find_by_name(&host_machine->kmaps, MAP__FUNCTION, module_name);
+		if (map) {
+			dso = map->dso;
+			goto found;
 		}
 		pr_debug("Failed to find module %s.\n", module);
 		return -ENOENT;
--
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