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

Indu Bhagat
2025-01-28T15:35:43Z

On 1/27/25 1:33 PM, Weinan Liu wrote:
> This patchset implements a generic kernel sframe-based [1] unwinder.
> The main goal is to support reliable stacktraces on arm64.
>
> On x86 orc unwinder provides reliable stacktraces. But arm64 misses the
> required support from objtool: it cannot generate orc unwind tables for
> arm64.
>
> Currently, there's already a sframe unwinder proposed for userspace: [2].
> Since the sframe unwind table algorithm is similar, these two proposal
> could integrate common functionality in the future.
>
> There are some incomplete features or challenges:
> - The unwinder doesn't yet work with kernel modules. The `start_addr` of
> FRE from kernel modules doesn't appear correct, preventing us from
> unwinding functions from kernel modules.

I did file https://sourceware.org/bugzilla/show_bug.cgi?id=32589
earlier. It is misleading (and inconvenient) to see all 0s in the dump
of non-relocated SFrame section.

I get the sense that while issue 32589 may be causing confusion that the
SFrame data is not correct, the problem is elsewhere ?

I can share a fix for 32589 so atleast we can verify that the starting
point is sane.

> - Currently, only GCC supports sframe.
>
> Ref:
> [1]: https://sourceware.org/binutils/docs/sframe-spec.html
> [2]: https://lore.kernel.org/lkml/cover.1730150953.git.jpoimboe@kernel.org/
>
> Madhavan T. Venkataraman (1):
> arm64: Define TIF_PATCH_PENDING for livepatch
>
> Weinan Liu (7):
> unwind: build kernel with sframe info
> arm64: entry: add unwind info for various kernel entries
> unwind: add sframe v2 header
> unwind: Implement generic sframe unwinder library
> unwind: arm64: Add sframe unwinder on arm64
> unwind: arm64: add reliable stacktrace support for arm64
> arm64: Enable livepatch for ARM64
>
> Makefile | 6 +
> arch/Kconfig | 8 +
> arch/arm64/Kconfig | 3 +
> arch/arm64/Kconfig.debug | 10 +
> arch/arm64/include/asm/stacktrace/common.h | 6 +
> arch/arm64/include/asm/thread_info.h | 4 +-
> arch/arm64/kernel/entry-common.c | 4 +
> arch/arm64/kernel/entry.S | 10 +
> arch/arm64/kernel/setup.c | 2 +
> arch/arm64/kernel/stacktrace.c | 102 ++++++++++
> include/asm-generic/vmlinux.lds.h | 12 ++
> include/linux/sframe_lookup.h | 43 +++++
> kernel/Makefile | 1 +
> kernel/sframe.h | 215 +++++++++++++++++++++
> kernel/sframe_lookup.c | 196 +++++++++++++++++++
> 15 files changed, 621 insertions(+), 1 deletion(-)
> create mode 100644 include/linux/sframe_lookup.h
> create mode 100644 kernel/sframe.h
> create mode 100644 kernel/sframe_lookup.c
>