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 <[email protected]>
---
tools/perf/util/machine.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/tools/perf/util/machine.c b/tools/perf/util/machine.c
index 4e62843d51b7..11de3ca8d4fa 100644
--- 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;
--
2.41.0.487.g6d72f3e995-goog
On 25/07/23 03:19, Namhyung Kim wrote:
> 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 <[email protected]>
Acked-by: Adrian Hunter <[email protected]>
> ---
> tools/perf/util/machine.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/tools/perf/util/machine.c b/tools/perf/util/machine.c
> index 4e62843d51b7..11de3ca8d4fa 100644
> --- 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;
>