[PATCH] perf tools: Fixup end address of modules

[PATCH] perf tools: Fixup end address of modules

[Namhyung Kim]

In machine__create_module(), it reads /proc/modules to get a list of
modules in the system.  The file shows the start address (of text) and
the size of the module so it uses the info to reconstruct system memory
maps for symbol resolution.

But module memory consists of multiple segments and they can be
scaterred.  Currently perf tools assume they are contiguous and see some
overlaps.  This can confuse the tool when it finds a map containing a
given address.

As we mostly care about the function symbols in the text segment, it can
fixup the size or end address of modules when there's an overlap.  We
can use maps__fixup_end() which updates the end address using the start
address of the next map.

Ideally it should be able to track other segments (like data/rodata),
but that would require some changes in /proc/modules IMHO.

Reported-by: Blake Jones <blakejones@google.com>
Cc: Luis Chamberlain <mcgrof@kernel.org>
Cc: Petr Pavlu <petr.pavlu@suse.com>
Cc: Sami Tolvanen <samitolvanen@google.com>
Cc: Daniel Gomez <da.gomez@samsung.com>
Cc: linux-modules@vger.kernel.org
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
---
 tools/perf/util/machine.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/tools/perf/util/machine.c b/tools/perf/util/machine.c
index 27d5345d2b307a97..8bb34689e3ceeec4 100644
--- a/tools/perf/util/machine.c
+++ b/tools/perf/util/machine.c
@@ -1468,6 +1468,8 @@ static int machine__create_modules(struct machine *machine)
 	if (modules__parse(modules, machine, machine__create_module))
 		return -1;
 
+	maps__fixup_end(machine__kernel_maps(machine));
+
 	if (!machine__set_modules_path(machine))
 		return 0;
 
-- 
2.47.1.613.gc27f4b7a9f-goog

Re: [PATCH] perf tools: Fixup end address of modules

[Ian Rogers]

On Wed, Dec 18, 2024 at 2:04 PM Namhyung Kim <namhyung@kernel.org> wrote:
>
> In machine__create_module(), it reads /proc/modules to get a list of
> modules in the system.  The file shows the start address (of text) and
> the size of the module so it uses the info to reconstruct system memory
> maps for symbol resolution.
>
> But module memory consists of multiple segments and they can be
> scaterred.  Currently perf tools assume they are contiguous and see some

nit: s/scaterred/scattered/

> overlaps.  This can confuse the tool when it finds a map containing a
> given address.
>
> As we mostly care about the function symbols in the text segment, it can
> fixup the size or end address of modules when there's an overlap.  We
> can use maps__fixup_end() which updates the end address using the start
> address of the next map.
>
> Ideally it should be able to track other segments (like data/rodata),
> but that would require some changes in /proc/modules IMHO.
>
> Reported-by: Blake Jones <blakejones@google.com>
> Cc: Luis Chamberlain <mcgrof@kernel.org>
> Cc: Petr Pavlu <petr.pavlu@suse.com>
> Cc: Sami Tolvanen <samitolvanen@google.com>
> Cc: Daniel Gomez <da.gomez@samsung.com>
> Cc: linux-modules@vger.kernel.org
> Signed-off-by: Namhyung Kim <namhyung@kernel.org>

Acked-by: Ian Rogers <irogers@google.com>

Thanks,
Ian

> ---
>  tools/perf/util/machine.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/tools/perf/util/machine.c b/tools/perf/util/machine.c
> index 27d5345d2b307a97..8bb34689e3ceeec4 100644
> --- a/tools/perf/util/machine.c
> +++ b/tools/perf/util/machine.c
> @@ -1468,6 +1468,8 @@ static int machine__create_modules(struct machine *machine)
>         if (modules__parse(modules, machine, machine__create_module))
>                 return -1;
>
> +       maps__fixup_end(machine__kernel_maps(machine));
> +
>         if (!machine__set_modules_path(machine))
>                 return 0;
>
> --
> 2.47.1.613.gc27f4b7a9f-goog
>

Re: [PATCH] perf tools: Fixup end address of modules

[Arnaldo Carvalho de Melo]

On Wed, Dec 18, 2024 at 02:15:35PM -0800, Ian Rogers wrote:
> On Wed, Dec 18, 2024 at 2:04 PM Namhyung Kim <namhyung@kernel.org> wrote:
> >
> > In machine__create_module(), it reads /proc/modules to get a list of
> > modules in the system.  The file shows the start address (of text) and
> > the size of the module so it uses the info to reconstruct system memory
> > maps for symbol resolution.
> >
> > But module memory consists of multiple segments and they can be
> > scaterred.  Currently perf tools assume they are contiguous and see some
> 
> nit: s/scaterred/scattered/
> 
> > overlaps.  This can confuse the tool when it finds a map containing a
> > given address.
> >
> > As we mostly care about the function symbols in the text segment, it can
> > fixup the size or end address of modules when there's an overlap.  We
> > can use maps__fixup_end() which updates the end address using the start
> > address of the next map.
> >
> > Ideally it should be able to track other segments (like data/rodata),
> > but that would require some changes in /proc/modules IMHO.
> >
> > Reported-by: Blake Jones <blakejones@google.com>
> > Cc: Luis Chamberlain <mcgrof@kernel.org>
> > Cc: Petr Pavlu <petr.pavlu@suse.com>
> > Cc: Sami Tolvanen <samitolvanen@google.com>
> > Cc: Daniel Gomez <da.gomez@samsung.com>
> > Cc: linux-modules@vger.kernel.org
> > Signed-off-by: Namhyung Kim <namhyung@kernel.org>
> 
> Acked-by: Ian Rogers <irogers@google.com>

Thanks, applied to perf-tools-next,

- Arnaldo