Re: [PATCH perf-tools-next v2 0/4] perf trace: Symbolise kernel virtual addresses and function pointers

[Ian Rogers]

On Sun, Aug 16, 2026 at 1:59 PM Aaron Tomlin <atomlin@xxxxxxxxxxx> wrote:
>
> When inspecting kernel execution flows using perf trace (e.g., when
> monitoring workqueues delayed work items, timer callbacks, etc.),
> tracepoint payload arguments containing raw kernel virtual addresses are
> currently rendered as hexadecimal values (e.g., 0xffffffff81234567).
>
> This requires manual symbol lookups against /proc/kallsyms or vmlinux to
> identify the underlying kernel function being executed.
>
> This patch series enhances perf trace by introducing kernel virtual
> address and function pointer symbolisation using perfs native symbol
> engine (i.e., machine__find_kernel_symbol()).
>
>     Before:
>       workqueue:workqueue_execute_end(work: 0xffffffffab2f1420, function: 0xffffffffa8046b50)
>
>     After:
>       workqueue:workqueue_execute_end(work: 0xffff8ac2c420f270, function: wb_update_bandwidth_workfn)

This looks great and a test! I noticed Sashiko feedback on patches 2,
3 and 4. It looked appropriate and actionable. I'm looking forward to
the next version and testing!

Thanks,
Ian

> Patch 1 introduces the syscall_arg__scnprintf_ksym() (SCA_KSYM) beautifier,
> which resolves virtual addresses via machine__find_kernel_symbol(),
> formatting them as symbol_name+offset (or "NULL", with a graceful
> hexadecimal fallback upon lookup failure).
>
> Patch 2 updates event format initialisation in
> syscall_arg_fmt__init_array() to automatically assign SCA_KSYM to
> tracepoint fields typed as function pointers (such as typedefs ending in
> "_func_t" or "_fn", or function prototypes matching "(*)"), as well as
> pointer or 64-bit address fields named "fn", "function", "callsite", or
> "call_site".
>
> Patch 3 extends BTF pretty-printing in trace__btf_scnprintf() with
> btf_is_func_ptr() to automatically traverse BTF type hierarchies (including
> nested typedefs and qualifiers) and route kernel function pointer arguments
> to SCA_KSYM when BTF metadata is available.
>
> Patch 4 adds an automated regression test script, trace_ksym_beautifier.sh,
> under tools/perf/tests/shell/ to verify symbolisation across both default
> kallsyms and BTF routing paths.
>
> Changes since v1:
>
>  - Fixed reference leak of struct map in syscall_arg__scnprintf_ksym() by
>    calling map__put() prior to returning Removed unreachable and erroneous
>    entries ("action", "callsite", "call_site", "fn", "function", "work")
>    from syscall_arg_fmts__by_name[]
>
>  - Restricted name-based SCA_KSYM auto-assignment in
>    syscall_arg_fmt__init_array() to pointer or 64-bit address fields,
>    preventing misclassification of non-pointer integer fields
>
>  - Updated btf_is_func_ptr() to fully unwrap typedefs and type modifiers
>    below pointer targets
>
>  - Fixed BTF type name matching in syscall_arg_fmt__cache_btf_type() to
>    handle leading modifiers and strip trailing pointer asterisks before
>    lookup
>
>  - Synchronised arg->val with val in trace__btf_scnprintf() and widened val
>    to unsigned long, fixing erroneous "NULL" output
>
>  - Added shell test script,
>    tools/perf/tests/shell/trace_ksym_beautifier.sh, to verify kernel symbol
>    beautification for both default kallsyms and BTF routing
>
>  - Link to v1: https://lore.kernel.org/lkml/20260815233651.527936-1-atomlin@xxxxxxxxxxx/
>
> Aaron Tomlin (4):
>   perf trace: Introduce kernel symbol beautifier for virtual addresses
>   perf trace: Auto-assign kernel symbol beautifier to function pointer
>     fields
>   perf trace: Enhance BTF type formatting to symbolise kernel function
>     pointers
>   perf tests: Add shell test for kernel symbol beautifier
>
>  tools/perf/builtin-trace.c                    | 103 ++++++++++++++++--
>  tools/perf/tests/shell/trace_btf_general.sh   |   2 +-
>  .../perf/tests/shell/trace_ksym_beautifier.sh |  52 +++++++++
>  tools/perf/trace/beauty/beauty.h              |   3 +
>  4 files changed, 148 insertions(+), 12 deletions(-)
>  create mode 100755 tools/perf/tests/shell/trace_ksym_beautifier.sh
>
> --
> 2.55.0
>