linux-kernel - Re: [PATCH v4 0/9] perf tools: Some improvements on data type profiler

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Message-ID: <aPgoVTfCFxqTpCaK@google.com>
Date: Wed, 22 Oct 2025 09:41:57 +0900
From: Namhyung Kim <namhyung@...nel.org>
To: Zecheng Li <zecheng@...gle.com>
Cc: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Jiri Olsa <jolsa@...nel.org>, Ian Rogers <irogers@...gle.com>,
	Adrian Hunter <adrian.hunter@...el.com>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Xu Liu <xliuprof@...gle.com>, linux-perf-users@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 0/9] perf tools: Some improvements on data type
 profiler

Hello,

On Mon, Oct 13, 2025 at 06:15:57PM +0000, Zecheng Li wrote:
> Hi all,
> 
> I've identified several missing data type annotations within the perf
> tools when annotating the Linux kernel. This patch series improves the
> coverage and correctness of data type annotations.
> 
> Some patches from the previous version of this series were
> cherry-picked. This revision adds new improvements based on feedback and
> further development.
> 
> Here's a breakdown of the changes in this revision:
> 
> Patch 1 skips annotations for LEA instructions in x86, as these do not
> involve memory access. It now returns NO_TYPE.
> 
> Patches 2 implements the TSR_KIND_POINTER to represent registers holding
> memory addresses of the type. We are using the size of void* to get the
> pointer size. This could be improved to use an architecture dependent
> pointer size, but may require more work.
> 
> Patches 3-5 implement a basic approach for register offset tracking that
> supports add, sub, and lea operations. The register state is invalidated
> when an unsupported arithmetic instruction is encountered. This revision
> uses TSR_KIND_POINTER to avoid finding the pointer type in DWARF and
> preserves the pointer offset information in the stack state.

I've applied up to this to perf-tools-next, will review the rest later.

Thanks,
Namhyung

> 
> Patches 6-8 split patch 8 from v2 with some minor improvements. It skips
> check_variable when the type is found directly by register, since
> sufficient checking is already performed in match_var_offset.
> check_variable lacks some DWARF information to correctly determine if a
> variable is valid. I also found it is able to find members for
> typedef'd types so I preserve them in match_var_offset.
> 
> Patch 9 implements support for DW_OP_piece. Currently, this is allowed
> in check_allowed_ops but is handled like other single location
> expressions. This patch splits any expression containing DW_OP_piece
> into multiple parts and handle them separately.
> 
> I have tested each patch on a vmlinux and manually checked the results.
> After applying all patches, there are less missing or incorrect
> annotations. No obvious regressions were observed.
> 
> v4:
> Merged patch in v3:
> perf annotate: Rename TSR_KIND_POINTER to TSR_KIND_PERCPU_POINTER
> 
> Updated patches 1-5 based on the feedback from Namhyung.
> 
> v3:
> https://lore.kernel.org/all/20250917195808.2514277-1-zecheng@google.com/
> Merged patches in v2:
> 
> perf dwarf-aux: Use signed variable types in match_var_offset
> perf dwarf-aux: More accurate variable type match for breg
> perf dwarf-aux: Better variable collection for insn tracking
> perf dwarf-aux: Skip check_variable for die_find_variable_by_reg
> 
> v2:
> https://lore.kernel.org/all/20250825195412.223077-1-zecheng@google.com/
> 1. update the match_var_offset function signature to s64
> 2. correct the comment for is_breg_access_indirect. Use simpler logic to
> match the expressions we support.
> 3. add is_reg_var_addr to indicate whether a register holds an address
> of the variable. This defers the type dereference logic to
> update_var_state.
> 4. invalidate register state for unsupported instructions.
> 5. include two new patches related to improving data type profiler.
> 
> v1:
> https://lore.kernel.org/linux-perf-users/20250725202809.1230085-1-zecheng@google.com/
> 
> Zecheng Li (9):
>   perf annotate: Skip annotating data types to lea instructions
>   perf annotate: Track address registers via TSR_KIND_POINTER
>   perf annotate: Track arithmetic instructions on pointers
>   perf annotate: Save pointer offset in stack state
>   perf annotate: Invalidate register states for untracked instructions
>   perf dwarf-aux: Skip check_variable for die_find_variable_by_reg
>   perf dwarf-aux: Preserve typedefs in match_var_offset
>   perf annotate: Improve type comparison from different scopes
>   perf dwarf-aux: Support DW_OP_piece expressions
> 
>  tools/perf/arch/x86/annotate/instructions.c | 183 +++++++++++++-
>  tools/perf/util/annotate-data.c             | 102 ++++++--
>  tools/perf/util/annotate-data.h             |  14 +-
>  tools/perf/util/annotate.c                  |  20 ++
>  tools/perf/util/dwarf-aux.c                 | 266 +++++++++++++++-----
>  tools/perf/util/dwarf-aux.h                 |   2 +-
>  6 files changed, 493 insertions(+), 94 deletions(-)
> 
> -- 
> 2.51.0
>