perf machine: Include data symbols in the kernel map

When 'perf record -d' is used, it needs data mmaps to symbolize global
data.  But it missed to collect kernel data maps so it cannot symbolize
them.  Instead of having a separate map, just increase the kernel map
size to include the data section.

Probably we can have a separate kernel map for data, but the current
code assumes a single kernel map.  So it'd require more changes in other
places and looks error-prone.  I decided not to go that way for now.

Also it seems the kernel module size already includes the data section.

For example, my system has the following.

  $ grep -e _stext -e _etext -e _edata /proc/kallsyms
  ffffffff99800000 T _stext
  ffffffff9a601ac8 T _etext
  ffffffff9b446a00 D _edata

Size of the text section is (0x9a601ac8 - 0x99800000 = 0xe01ac8) and
size including data section is (0x9b446a00 - 0x99800000 = 0x1c46a00).

Before:
  $ perf record -d true

  $ perf report -D | grep MMAP | head -1
  0 0 0x460 [0x60]: PERF_RECORD_MMAP -1/0: [0xffffffff99800000(0xe01ac8) @ 0xffffffff99800000]: x [kernel.kallsyms]_text
                                                               ^^^^^^^^
                                                                 here
After:
  $ perf report -D | grep MMAP | head -1
  0 0 0x460 [0x60]: PERF_RECORD_MMAP -1/0: [0xffffffff99800000(0x1c46a00) @ 0xffffffff99800000]: x [kernel.kallsyms]_text
                                                               ^^^^^^^^^

Instead of just replacing it to _edata, try _edata first and then fall
back to _etext just in case.

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20230725001929.368041-2-namhyung@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

diff --git a/tools/perf/util/machine.c b/tools/perf/util/machine.c
index 4e62843d51b7dbf9f930594db3699b36c36b9082..11de3ca8d4fa75222d681cd6bafa7d136e1907be 100644 (file)
--- a/tools/perf/util/machine.c
+++ b/tools/perf/util/machine.c
@@ -1216,7 +1216,9 @@ static int machine__get_running_kernel_start(struct machine *machine,
 
        *start = addr;
 
-       err = kallsyms__get_function_start(filename, "_etext", &addr);
+       err = kallsyms__get_symbol_start(filename, "_edata", &addr);
+       if (err)
+               err = kallsyms__get_function_start(filename, "_etext", &addr);
        if (!err)
                *end = addr;