Re: [PATCH v5 0/8] unwind, arm64: add sframe unwinder for kernel

[Mark Rutland <mark.rutland@arm.com>]

Hi Dylan,

On Tue, Apr 28, 2026 at 06:36:35PM +0000, Dylan Hatch wrote:
> Implement a generic kernel sframe-based [1] unwinder. The main goal is
> to improve reliable stacktrace on arm64 by unwinding across exception
> boundaries.

Thanks for this!

Just as a holding reply: I'm going over the series now, and I have some
partially-written comments that I'll try to finish up and get out
tomorrow.

Mark.

> On x86, the ORC unwinder provides reliable stacktrace through similar
> methodology, but arm64 lacks the necessary support from objtool to
> create ORC unwind tables.
> 
> Currently, there's already a sframe unwinder proposed for userspace: [2].
> To maintain common definitions and algorithms for sframe lookup, a
> substantial portion of this patch series aims to refactor the sframe
> lookup code to support both kernel and userspace sframe sections.
> 
> Currently, only GNU Binutils support sframe. This series relies on the
> Sframe V3 format, which is supported in binutils 2.46.
> 
> These patches are based on Steven Rostedt's sframe/core branch [3],
> which is and aggregation of existing work done for x86 sframe userspace
> unwind, and contains [2]. This branch is, in turn, based on Linux
> v7.0-rc3. This full series (applied to the sframe/core branch) is
> available on github: [4].
> 
> Ref:
> [1]: https://sourceware.org/binutils/docs/sframe-spec.html
> [2]: https://lore.kernel.org/lkml/20260127150554.2760964-1-jremus@linux.ibm.com/
> [3]: https://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace.git/log/?h=sframe/core
> [4]: https://github.com/dylanbhatch/linux/tree/sframe-v5
> 
> Changes since v4:
>   - (Jens) Fix some minor nits.
>   - Handle .init.text and .exit.text in function address validation.
> 
> Changes since v3:
> 
>   - (Jens) Clean up patch summaries.
>   - (Jens) Rename SFRAME_LOOKUP -> UNWIND_SFRAME_LOOKUP to fit existing
>     naming convention.
>   - (Randy) Correct typo errors in new config options.
>   - (Jens) Move unwind types to a new unwind_types.h to match their
>     usage.
>   - (Jens) Update KERNEL_[COPY|GET] to use label-based error handling
>     like their userspace counterparts.
>   - (Jens) Rename SFRAME_UNWINDER -> HAVE_UNWIND_KERNEL_SFRAME and
>     ARCH_SUPPORTS_SFRAME_UNWINDER -> ARCH_SUPPORTS_UNWIND_KERNEL_SFRAME
>     to match existing naming convention.
>   - (Jens) Move HAVE_UNWIND_KERNEL_SFRAME config option to arch/Kconfig.
>   - (Jens) Rename/move extern definitions of __[start|end]_sframe into
>     include/asm-generic/sections.h.
>   - (Jens) Fix up CFI annotations at kernel entry.
>   - (Jens) Fix error path for unsorted FDE lookup.
>   - (Jens) Zero-out module sframe_section before init.
>   - (Jens) For SFRAME_VALIDATION, use an arch-specific function-address
>     validation helper so that .rodata.text can be correctly handled on
>     arm64 vmlinux.
>   - (Jens) Fixup and better comment kernel stacktrace code.
> 
> Changes since v2:
> 
> The biggest change from v2 is the switch from adding a dedicated,
> in-kernel sframe-lookup library, to refactoring/using the existing
> library developed by Josh, Jens, and Steve. Consequently, this series
> now depends on Sframe V3, though this upgrade would likely have been
> necessary anyway. Below is a full accounting of the changes since v2.
> 
>   - (Josh) Add stricter reliability checks during unwind.
>   - (Puranjay, Indu, Jens) Update to use a common sframe library with
>     userpace unwind, thus resolving the need to support
>     SFRAME_F_FDE_FUNC_START_PCREL, added in binutils 2.45.
>   - (Jens) Add check for sframe V3, thus resolving the prior need for V2
>     and SFRAME_F_FDE_FUNC_START_PCREL support.
>   - (Will) Add ARCH_SUPPORTS_SFRAME_UNWINDER, remove SFRAME_UNWIND_TABLE
>   - (Indu) add support for unsorted FDE tables, allowing for module
>     sframe lookups.
>   - (Mark) Prefer frame-pointer unwind when possible, for better
>     performance.
>   - Simplify compile-time logic, adding stubbs when necessary.
>   - Add support for in-kernel SFRAME_VALIDATION.
>   - Rebase onto core/sframe (with v7.0-rc3 base)
> 
> Dylan Hatch (7):
>   sframe: Allow kernelspace sframe sections
>   arm64, unwind: build kernel with sframe V3 info
>   sframe: Provide PC lookup for vmlinux .sframe section
>   sframe: Allow unsorted FDEs
>   arm64/module, sframe: Add sframe support for modules
>   sframe: Introduce in-kernel SFRAME_VALIDATION
>   unwind: arm64: Use sframe to unwind interrupt frames
> 
> Weinan Liu (1):
>   arm64: entry: add unwind info for various kernel entries
> 
>  MAINTAINERS                                   |   3 +-
>  Makefile                                      |   8 +
>  arch/Kconfig                                  |  27 +-
>  arch/arm64/Kconfig                            |   1 +
>  arch/arm64/include/asm/module.h               |   6 +
>  arch/arm64/include/asm/sections.h             |   1 +
>  arch/arm64/include/asm/stacktrace/common.h    |   6 +
>  arch/arm64/include/asm/unwind_sframe.h        |  55 +++
>  arch/arm64/kernel/entry.S                     |  23 +
>  arch/arm64/kernel/module.c                    |   8 +
>  arch/arm64/kernel/setup.c                     |   2 +
>  arch/arm64/kernel/stacktrace.c                | 246 ++++++++++-
>  arch/arm64/kernel/vdso/Makefile               |   2 +-
>  arch/arm64/kernel/vmlinux.lds.S               |   2 +
>  .../{unwind_user_sframe.h => unwind_sframe.h} |   6 +-
>  arch/x86/include/asm/unwind_user.h            |  12 +-
>  include/asm-generic/sections.h                |   4 +
>  include/asm-generic/vmlinux.lds.h             |  15 +
>  include/linux/sframe.h                        |  67 ++-
>  include/linux/unwind_types.h                  |  46 ++
>  include/linux/unwind_user_types.h             |  41 --
>  kernel/unwind/Makefile                        |   2 +-
>  kernel/unwind/sframe.c                        | 410 ++++++++++++++----
>  kernel/unwind/user.c                          |  41 +-
>  24 files changed, 827 insertions(+), 207 deletions(-)
>  create mode 100644 arch/arm64/include/asm/unwind_sframe.h
>  rename arch/x86/include/asm/{unwind_user_sframe.h => unwind_sframe.h} (50%)
>  create mode 100644 include/linux/unwind_types.h
> 
> -- 
> 2.54.0.545.g6539524ca2-goog
>