linux-kernel - [PATCH] perf buildid: Fix cpumode of buildid event

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Date:	Fri, 29 Jan 2016 17:40:51 +0000
From:	Wang Nan <wangnan0@...wei.com>
To:	<jolsa@...hat.com>, <acme@...nel.org>
CC:	<linux-kernel@...r.kernel.org>, <pi3orama@....com>,
	Wang Nan <wangnan0@...wei.com>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	"Masami Hiramatsu" <masami.hiramatsu.pt@...achi.com>,
	Namhyung Kim <namhyung@...nel.org>,
	Li Zefan <lizefan@...wei.com>
Subject: [PATCH] perf buildid: Fix cpumode of buildid event

There is a nasty confusion that, for kernel module, dso->kernel
is not necessary to be DSO_TYPE_KERNEL or DSO_TYPE_GUEST_KERNEL.
These two enums are for vmlinux. See thread [1]. We tried to fix
this part but it is costy.

Code machine__write_buildid_table() is another unfortunate function
fall into this trap that, when issuing buildid event for a kernel
module, cpumode it gives to the event is PERF_RECORD_MISC_USER, not
PERF_RECORD_MISC_KERNEL.

However, even with this bug, most of the time it doesn't causes real
problem. I find this issue when trying to use a perf before commit
3d39ac538629 ("perf machine: No need to have two DSOs lists") to parse
a perf.data generated by newest perf.

[1] https://lkml.org/lkml/2015/9/21/908

Signed-off-by: Wang Nan <wangnan0@...wei.com>
Cc: Arnaldo Carvalho de Melo <acme@...hat.com>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
Cc: Namhyung Kim <namhyung@...nel.org>
Cc: Li Zefan <lizefan@...wei.com>
---
 tools/perf/util/build-id.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/tools/perf/util/build-id.c b/tools/perf/util/build-id.c
index 6b18082..f1479ee 100644
--- a/tools/perf/util/build-id.c
+++ b/tools/perf/util/build-id.c
@@ -255,6 +255,7 @@ static int machine__write_buildid_table(struct machine *machine, int fd)
 	dsos__for_each_with_build_id(pos, &machine->dsos.head) {
 		const char *name;
 		size_t name_len;
+		bool in_kernel = false;
 
 		if (!pos->hit)
 			continue;
@@ -271,8 +272,11 @@ static int machine__write_buildid_table(struct machine *machine, int fd)
 			name_len = pos->long_name_len + 1;
 		}
 
+		in_kernel = pos->kernel ||
+				is_kernel_module(name,
+					PERF_RECORD_MISC_CPUMODE_UNKNOWN);
 		err = write_buildid(name, name_len, pos->build_id, machine->pid,
-				    pos->kernel ? kmisc : umisc, fd);
+				    in_kernel ? kmisc : umisc, fd);
 		if (err)
 			break;
 	}
-- 
1.8.3.4