linux-kernel - Re: [PATCH v2 0/2] perf maps: Improve the kcore maps merging

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Date: Wed, 15 May 2024 14:39:58 -0700
From: Ian Rogers <irogers@...gle.com>
To: Leo Yan <leo.yan@....com>
Cc: Arnaldo Carvalho de Melo <acme@...nel.org>, Adrian Hunter <adrian.hunter@...el.com>, 
	James Clark <james.clark@....com>, Peter Zijlstra <peterz@...radead.org>, 
	Ingo Molnar <mingo@...hat.com>, Namhyung Kim <namhyung@...nel.org>, 
	Mark Rutland <mark.rutland@....com>, 
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>, Jiri Olsa <jolsa@...nel.org>, 
	Athira Rajeev <atrajeev@...ux.vnet.ibm.com>, linux-perf-users@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 0/2] perf maps: Improve the kcore maps merging

On Wed, May 15, 2024 at 2:11 PM Leo Yan <leo.yan@....com> wrote:
>
> This patch series follows up on the patch [1] to improve the sorting and
> merging of kcore maps.
>
> Since the kcore maps are not sorted, merging them into the kernel maps
> causes difficulty, e.g. some kcore maps might be ignored. This is why
> the dso__load_kcore() function handles the kernel text section
> particularly for replacement a complete kernel section.
>
> This patch sorts the kcore maps and ensures the subset region is placed
> ahead of the superset region in the list. With this change, merging
> these maps becomes easier - no need the special handling for the kernel
> text section.
>
> This patch series is based on the latest acme's perf-tool-next branch
> and tested on Arm64 Hikey960 board.
>
> [1] https://lore.kernel.org/linux-perf-users/438f8725-ef3f-462f-90e2-840cab478ee5@arm.com/T/#m7c86a69d43103cd0cb446b0993e47c36df0f40f2

Thanks Leo, testing this change on perf-tools-next with an x86 debian
laptop I see:
```
$ perf test 24 -v
24: Object code reading:
--- start ---
test child forked, pid 3407499
Looking at the vmlinux_path (8 entries long)
symsrc__init: build id mismatch for vmlinux.
symsrc__init: cannot get elf header.
overlapping maps in [kernel.kallsyms] (disable tui for more info)
Using /proc/kcore for kernel data
Using /proc/kallsyms for symbols
Parsing event 'cycles'
Using CPUID GenuineIntel-6-8D-1
mmap size 528384B
Reading object code for memory address: 0xfffffffface8d64a
File is: /proc/kcore
On file address is: 0xfffffffface8d64a
dso__data_read_offset failed
---- end(-1) ----
24: Object code reading                                             : FAILED!
```
The test passes without the changes. Let me know if you need me to dig deeper.

Thanks,
Ian

> Leo Yan (2):
>   perf maps: Sort kcore maps
>   perf maps: Remove the replacement of kernel map
>
>  tools/perf/util/symbol.c | 117 +++++++++++++++++++--------------------
>  1 file changed, 57 insertions(+), 60 deletions(-)
>
> --
> 2.34.1
>