[PATCH 0/4] Handle chroot tasks properly (v2)

[PATCH 0/4] Handle chroot tasks properly (v2)

[Namhyung Kim]

Hello,

I found that perf tools don't work well with tasks in a chroot.  The
filenames in MMAP record are from the root directory of the task so
it's different than what it sees from outside.

 * changes in v2)
  - add Jiri's Acked-by
  - split stderr setup for objdump

I've tested it with a simple program (myprog - statically built) which
just consumes cpu cycles in a loop for a while (default 1 sec, can by
overridden by a command-line argument).

  # cd $HOME
  # mkdir -p myroot/bin
  # cp myprog myroot/bin

  # perf record chroot myroot myprog
  # perf report -D | grep MMAP | grep myprog
  2084916774977911 0xa2e4 [0x70]: PERF_RECORD_MMAP2 3363818/3363818: \
  [0x401000(0x80000) @ 0x1000 fe:01 4346398 2543719070]: r-xp /bin/myprog

So it's reported as /bin/myprog and then it's unable to symbolize the
samples.  It seems hard to fix it for the above use case as the record
ended after the task exited.  It cannot know the root directory of the
task anymore.  But we can fix it for real-time use cases like perf top
or pipe-mode at least.

I tested it again with the following command.

  # perf record -o- chroot myroot myprog | perf report -i-
  ...
  #
  # Overhead  Command  Shared Object      Symbol                          
  # ........  .......  .................  ................................
  #
      46.02%  myprog   myprog             [.] 0x000000000000178a
      36.71%  myprog   myprog             [.] 0x0000000000001792
      17.12%  myprog   myprog             [.] 0x000000000000178e
       0.05%  myprog   myprog             [.] 0x0000000000001796
       0.05%  chroot   ld-2.33.so         [.] intel_check_word.constprop.0

The symbols are not resolved because it failed to load the symbol
table as it didn't find the file in the given path.

So I modified the code to try a new name prepended with the task's
root directory when it's not "/".  With this change, I can see the
symbols of myprog.  In fact, it depends on timing if perf report hits
the file before the task is gone.  Increasing the loop time to 3 sec
helped it to get symbols reliably.

  # perf record -o- chroot myroot myprog 3 | perf report -i-
  ...
  #
  # Overhead  Command  Shared Object      Symbol                       
  # ........  .......  .................  .............................
  #
      99.83%  myprog   myprog             [.] loop
       0.04%  chroot   [kernel.kallsyms]  [k] fxregs_fixup
       0.04%  chroot   [kernel.kallsyms]  [k] rsm_load_seg_32
       0.03%  chroot   [kernel.kallsyms]  [k] show_cpuinfo_cur_freq
       0.01%  myprog   [kernel.kallsyms]  [k] alarmtimer_fired


I also found that perf inject and perf annotate need the similar changes.

You can get it from 'perf/dso-chroot-v2' branch at

  git://git.kernel.org/pub/scm/linux/kernel/git/namhyung/linux-perf.git


Thanks,
Namhyung


Namhyung Kim (4):
  perf annotate: Set error stream of objdump process for TUI
  perf tools: Try chroot'ed filename when opening dso/symbol
  perf inject: Try chroot directory when reading build-id
  perf annotate: Try chroot filename for objdump

 tools/perf/builtin-inject.c | 10 ++++++++++
 tools/perf/util/annotate.c  | 11 +++++++++++
 tools/perf/util/dso.c       | 15 +++++++++++++--
 tools/perf/util/dsos.c      | 13 +++++++++++++
 tools/perf/util/symbol.c    | 10 ++++++++++
 tools/perf/util/util.c      | 31 +++++++++++++++++++++++++++++++
 tools/perf/util/util.h      |  2 ++
 7 files changed, 90 insertions(+), 2 deletions(-)


base-commit: e783362eb54cd99b2cac8b3a9aeac942e6f6ac07
-- 
2.35.0.rc2.247.g8bbb082509-goog

[PATCH 1/4] perf annotate: Set error stream of objdump process for TUI

[Namhyung Kim]

The stderr should be set to a pipe when using TUI.  Otherwise it'd
print to stdout and break TUI windows with an error message.

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
---
 tools/perf/util/annotate.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/tools/perf/util/annotate.c b/tools/perf/util/annotate.c
index 01900689dc00..8190a124b99d 100644
--- a/tools/perf/util/annotate.c
+++ b/tools/perf/util/annotate.c
@@ -2036,6 +2036,7 @@ static int symbol__disassemble(struct symbol *sym, struct annotate_args *args)
 	memset(&objdump_process, 0, sizeof(objdump_process));
 	objdump_process.argv = objdump_argv;
 	objdump_process.out = -1;
+	objdump_process.err = -1;
 	if (start_command(&objdump_process)) {
 		pr_err("Failure starting to run %s\n", command);
 		err = -1;
-- 
2.35.0.rc2.247.g8bbb082509-goog

[PATCH 2/4] perf tools: Try chroot'ed filename when opening dso/symbol

[Namhyung Kim]

Currently it doesn't handle tasks in chroot properly.  As filenames in
MMAP records base on their root directory, it's different than what
perf tool can see from outside.

Add filename_with_chroot() helper to deal with those cases.  The
function returns a new filename only if it's in a different root
directory.  Since it needs to access /proc for the process, it only
works until the task exits.

With this change, I can see symbols in my program like below.

  # perf record -o- chroot myroot myprog 3 | perf report -i-
  ...
  #
  # Overhead  Command  Shared Object      Symbol
  # ........  .......  .................  .............................
  #
      99.83%  myprog   myprog             [.] loop
       0.04%  chroot   [kernel.kallsyms]  [k] fxregs_fixup
       0.04%  chroot   [kernel.kallsyms]  [k] rsm_load_seg_32
  ...

Acked-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
---
 tools/perf/util/dso.c    | 15 +++++++++++++--
 tools/perf/util/dsos.c   | 13 +++++++++++++
 tools/perf/util/symbol.c | 10 ++++++++++
 tools/perf/util/util.c   | 31 +++++++++++++++++++++++++++++++
 tools/perf/util/util.h   |  2 ++
 5 files changed, 69 insertions(+), 2 deletions(-)

diff --git a/tools/perf/util/dso.c b/tools/perf/util/dso.c
index 9cc8a1772b4b..5ac13958d1bd 100644
--- a/tools/perf/util/dso.c
+++ b/tools/perf/util/dso.c
@@ -508,8 +508,19 @@ static int __open_dso(struct dso *dso, struct machine *machine)
 					    root_dir, name, PATH_MAX))
 		goto out;
 
-	if (!is_regular_file(name))
-		goto out;
+	if (!is_regular_file(name)) {
+		char *new_name;
+
+		if (errno != ENOENT || dso->nsinfo == NULL)
+			goto out;
+
+		new_name = filename_with_chroot(dso->nsinfo->pid, name);
+		if (!new_name)
+			goto out;
+
+		free(name);
+		name = new_name;
+	}
 
 	if (dso__needs_decompress(dso)) {
 		char newpath[KMOD_DECOMP_LEN];
diff --git a/tools/perf/util/dsos.c b/tools/perf/util/dsos.c
index 183a81d5b2f9..b97366f77bbf 100644
--- a/tools/perf/util/dsos.c
+++ b/tools/perf/util/dsos.c
@@ -2,12 +2,15 @@
 #include "debug.h"
 #include "dsos.h"
 #include "dso.h"
+#include "util.h"
 #include "vdso.h"
 #include "namespaces.h"
+#include <errno.h>
 #include <libgen.h>
 #include <stdlib.h>
 #include <string.h>
 #include <symbol.h> // filename__read_build_id
+#include <unistd.h>
 
 static int __dso_id__cmp(struct dso_id *a, struct dso_id *b)
 {
@@ -76,6 +79,16 @@ bool __dsos__read_build_ids(struct list_head *head, bool with_hits)
 		if (filename__read_build_id(pos->long_name, &pos->bid) > 0) {
 			have_build_id	  = true;
 			pos->has_build_id = true;
+		} else if (errno == ENOENT && pos->nsinfo) {
+			char *new_name = filename_with_chroot(pos->nsinfo->pid,
+							      pos->long_name);
+
+			if (new_name && filename__read_build_id(new_name,
+								&pos->bid) > 0) {
+				have_build_id = true;
+				pos->has_build_id = true;
+			}
+			free(new_name);
 		}
 		nsinfo__mountns_exit(&nsc);
 	}
diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c
index b2ed3140a1fa..34302c61d36b 100644
--- a/tools/perf/util/symbol.c
+++ b/tools/perf/util/symbol.c
@@ -1864,6 +1864,16 @@ int dso__load(struct dso *dso, struct map *map)
 			nsinfo__mountns_exit(&nsc);
 
 		is_reg = is_regular_file(name);
+		if (!is_reg && errno == ENOENT && dso->nsinfo) {
+			char *new_name = filename_with_chroot(dso->nsinfo->pid,
+							      name);
+			if (new_name) {
+				is_reg = is_regular_file(new_name);
+				strlcpy(name, new_name, PATH_MAX);
+				free(new_name);
+			}
+		}
+
 #ifdef HAVE_LIBBFD_SUPPORT
 		if (is_reg)
 			bfdrc = dso__load_bfd_symbols(dso, name);
diff --git a/tools/perf/util/util.c b/tools/perf/util/util.c
index fb4f6616b5fa..f8571a66d063 100644
--- a/tools/perf/util/util.c
+++ b/tools/perf/util/util.c
@@ -431,3 +431,34 @@ void perf_debuginfod_setup(struct perf_debuginfod *di)
 
 	pr_debug("DEBUGINFOD_URLS=%s\n", getenv("DEBUGINFOD_URLS"));
 }
+
+/*
+ * Return a new filename prepended with task's root directory if it's in
+ * a chroot.  Callers should free the returned string.
+ */
+char *filename_with_chroot(int pid, const char *filename)
+{
+	char buf[PATH_MAX];
+	char proc_root[32];
+	char *new_name = NULL;
+	int ret;
+
+	scnprintf(proc_root, sizeof(proc_root), "/proc/%d/root", pid);
+	ret = readlink(proc_root, buf, sizeof(buf) - 1);
+	if (ret <= 0)
+		return NULL;
+
+	/* readlink(2) does not append a null byte to buf */
+	buf[ret] = '\0';
+
+	if (!strcmp(buf, "/"))
+		return NULL;
+
+	if (strstr(buf, "(deleted)"))
+		return NULL;
+
+	if (asprintf(&new_name, "%s/%s", buf, filename) < 0)
+		return NULL;
+
+	return new_name;
+}
diff --git a/tools/perf/util/util.h b/tools/perf/util/util.h
index 7b625cbd2dd8..0f78f1e7782d 100644
--- a/tools/perf/util/util.h
+++ b/tools/perf/util/util.h
@@ -77,4 +77,6 @@ struct perf_debuginfod {
 	bool		 set;
 };
 void perf_debuginfod_setup(struct perf_debuginfod *di);
+
+char *filename_with_chroot(int pid, const char *filename);
 #endif /* GIT_COMPAT_UTIL_H */
-- 
2.35.0.rc2.247.g8bbb082509-goog

[PATCH 3/4] perf inject: Try chroot directory when reading build-id

[Namhyung Kim]

When reading build-id from a DSO, it should consider if it's from a
chroot task.  In that case, the path is different so it needs to
prepend the root directory to access the file correctly.

Acked-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
---
 tools/perf/builtin-inject.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/tools/perf/builtin-inject.c b/tools/perf/builtin-inject.c
index fbf43a454cba..3be581abbdb6 100644
--- a/tools/perf/builtin-inject.c
+++ b/tools/perf/builtin-inject.c
@@ -25,6 +25,7 @@
 #include "util/synthetic-events.h"
 #include "util/thread.h"
 #include "util/namespaces.h"
+#include "util/util.h"
 
 #include <linux/err.h>
 #include <subcmd/parse-options.h>
@@ -550,6 +551,15 @@ static int dso__read_build_id(struct dso *dso)
 	nsinfo__mountns_enter(dso->nsinfo, &nsc);
 	if (filename__read_build_id(dso->long_name, &dso->bid) > 0)
 		dso->has_build_id = true;
+	else if (dso->nsinfo) {
+		char *new_name;
+
+		new_name = filename_with_chroot(dso->nsinfo->pid,
+						dso->long_name);
+		if (new_name && filename__read_build_id(new_name, &dso->bid) > 0)
+			dso->has_build_id = true;
+		free(new_name);
+	}
 	nsinfo__mountns_exit(&nsc);
 
 	return dso->has_build_id ? 0 : -1;
-- 
2.35.0.rc2.247.g8bbb082509-goog

[PATCH 4/4] perf annotate: Try chroot filename for objdump

[Namhyung Kim]

Likewise, it should use a proper name in case the task runs under
chroot.

Acked-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
---
 tools/perf/util/annotate.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/tools/perf/util/annotate.c b/tools/perf/util/annotate.c
index 8190a124b99d..e4c641b240df 100644
--- a/tools/perf/util/annotate.c
+++ b/tools/perf/util/annotate.c
@@ -33,6 +33,7 @@
 #include "string2.h"
 #include "util/event.h"
 #include "arch/common.h"
+#include "namespaces.h"
 #include <regex.h>
 #include <pthread.h>
 #include <linux/bitops.h>
@@ -1696,6 +1697,15 @@ static int dso__disassemble_filename(struct dso *dso, char *filename, size_t fil
 		 * DSO is the same as when 'perf record' ran.
 		 */
 		__symbol__join_symfs(filename, filename_size, dso->long_name);
+
+		if (access(filename, R_OK) && errno == ENOENT && dso->nsinfo) {
+			char *new_name = filename_with_chroot(dso->nsinfo->pid,
+							      filename);
+			if (new_name) {
+				strlcpy(filename, new_name, filename_size);
+				free(new_name);
+			}
+		}
 	}
 
 	free(build_id_path);
-- 
2.35.0.rc2.247.g8bbb082509-goog

Re: [PATCH 0/4] Handle chroot tasks properly (v2)

[Arnaldo Carvalho de Melo]

Em Tue, Feb 01, 2022 at 11:08:24PM -0800, Namhyung Kim escreveu:
> Hello,
> 
> I found that perf tools don't work well with tasks in a chroot.  The
> filenames in MMAP record are from the root directory of the task so
> it's different than what it sees from outside.
> 
>  * changes in v2)
>   - add Jiri's Acked-by
>   - split stderr setup for objdump

Applied 1/4 to perf/urgent, its already upstream.

The others are bit big for this time, so I've added it to perf/core.

Thanks,

- Arnaldo
 
> I've tested it with a simple program (myprog - statically built) which
> just consumes cpu cycles in a loop for a while (default 1 sec, can by
> overridden by a command-line argument).
> 
>   # cd $HOME
>   # mkdir -p myroot/bin
>   # cp myprog myroot/bin
> 
>   # perf record chroot myroot myprog
>   # perf report -D | grep MMAP | grep myprog
>   2084916774977911 0xa2e4 [0x70]: PERF_RECORD_MMAP2 3363818/3363818: \
>   [0x401000(0x80000) @ 0x1000 fe:01 4346398 2543719070]: r-xp /bin/myprog
> 
> So it's reported as /bin/myprog and then it's unable to symbolize the
> samples.  It seems hard to fix it for the above use case as the record
> ended after the task exited.  It cannot know the root directory of the
> task anymore.  But we can fix it for real-time use cases like perf top
> or pipe-mode at least.
> 
> I tested it again with the following command.
> 
>   # perf record -o- chroot myroot myprog | perf report -i-
>   ...
>   #
>   # Overhead  Command  Shared Object      Symbol                          
>   # ........  .......  .................  ................................
>   #
>       46.02%  myprog   myprog             [.] 0x000000000000178a
>       36.71%  myprog   myprog             [.] 0x0000000000001792
>       17.12%  myprog   myprog             [.] 0x000000000000178e
>        0.05%  myprog   myprog             [.] 0x0000000000001796
>        0.05%  chroot   ld-2.33.so         [.] intel_check_word.constprop.0
> 
> The symbols are not resolved because it failed to load the symbol
> table as it didn't find the file in the given path.
> 
> So I modified the code to try a new name prepended with the task's
> root directory when it's not "/".  With this change, I can see the
> symbols of myprog.  In fact, it depends on timing if perf report hits
> the file before the task is gone.  Increasing the loop time to 3 sec
> helped it to get symbols reliably.
> 
>   # perf record -o- chroot myroot myprog 3 | perf report -i-
>   ...
>   #
>   # Overhead  Command  Shared Object      Symbol                       
>   # ........  .......  .................  .............................
>   #
>       99.83%  myprog   myprog             [.] loop
>        0.04%  chroot   [kernel.kallsyms]  [k] fxregs_fixup
>        0.04%  chroot   [kernel.kallsyms]  [k] rsm_load_seg_32
>        0.03%  chroot   [kernel.kallsyms]  [k] show_cpuinfo_cur_freq
>        0.01%  myprog   [kernel.kallsyms]  [k] alarmtimer_fired
> 
> 
> I also found that perf inject and perf annotate need the similar changes.
> 
> You can get it from 'perf/dso-chroot-v2' branch at
> 
>   git://git.kernel.org/pub/scm/linux/kernel/git/namhyung/linux-perf.git
> 
> 
> Thanks,
> Namhyung
> 
> 
> Namhyung Kim (4):
>   perf annotate: Set error stream of objdump process for TUI
>   perf tools: Try chroot'ed filename when opening dso/symbol
>   perf inject: Try chroot directory when reading build-id
>   perf annotate: Try chroot filename for objdump
> 
>  tools/perf/builtin-inject.c | 10 ++++++++++
>  tools/perf/util/annotate.c  | 11 +++++++++++
>  tools/perf/util/dso.c       | 15 +++++++++++++--
>  tools/perf/util/dsos.c      | 13 +++++++++++++
>  tools/perf/util/symbol.c    | 10 ++++++++++
>  tools/perf/util/util.c      | 31 +++++++++++++++++++++++++++++++
>  tools/perf/util/util.h      |  2 ++
>  7 files changed, 90 insertions(+), 2 deletions(-)
> 
> 
> base-commit: e783362eb54cd99b2cac8b3a9aeac942e6f6ac07
> -- 
> 2.35.0.rc2.247.g8bbb082509-goog

-- 

- Arnaldo

Re: [PATCH 0/4] Handle chroot tasks properly (v2)

[Namhyung Kim]

Hi Arnaldo,

On Thu, Feb 10, 2022 at 10:35 AM Arnaldo Carvalho de Melo
<acme@kernel.org> wrote:
>
> Em Tue, Feb 01, 2022 at 11:08:24PM -0800, Namhyung Kim escreveu:
> > Hello,
> >
> > I found that perf tools don't work well with tasks in a chroot.  The
> > filenames in MMAP record are from the root directory of the task so
> > it's different than what it sees from outside.
> >
> >  * changes in v2)
> >   - add Jiri's Acked-by
> >   - split stderr setup for objdump
>
> Applied 1/4 to perf/urgent, its already upstream.
>
> The others are bit big for this time, so I've added it to perf/core.

Perfect, thanks for your work!

Namhyung