1. Patchew
  2. linux
  3. View series

[PATCH v2 0/6] unwind, arm64: add sframe unwinder for kernel

Dylan Hatch posted 6 patches 4 weeks ago 
Makefile                                   |   8 +
arch/Kconfig                               |   6 +
arch/arm64/Kconfig.debug                   |  10 +
arch/arm64/include/asm/module.h            |   6 +
arch/arm64/include/asm/stacktrace/common.h |   6 +
arch/arm64/kernel/entry.S                  |  10 +
arch/arm64/kernel/module.c                 |   5 +
arch/arm64/kernel/setup.c                  |   2 +
arch/arm64/kernel/stacktrace.c             | 102 +++++++++
arch/arm64/kernel/vdso/Makefile            |   2 +-
include/asm-generic/vmlinux.lds.h          |  15 ++
include/linux/sframe_lookup.h              |  45 ++++
kernel/Makefile                            |   1 +
kernel/sframe.h                            |  75 +++++++
kernel/sframe_lookup.c                     | 232 +++++++++++++++++++++
15 files changed, 524 insertions(+), 1 deletion(-)
create mode 100644 include/linux/sframe_lookup.h
create mode 100644 kernel/sframe.h
create mode 100644 kernel/sframe_lookup.c
[PATCH v2 0/6] unwind, arm64: add sframe unwinder for kernel
Posted by Dylan Hatch 4 weeks ago 
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 proposals
could integrate common functionality in the future.

Currently, only GCC supports sframe.

These patches are based on v6.17-rc4 and are available on github [3].

Ref:
[1]: https://sourceware.org/binutils/docs/sframe-spec.html
[2]: https://lore.kernel.org/lkml/cover.1730150953.git.jpoimboe@kernel.org/
[3]: https://github.com/dylanbhatch/linux/tree/sframe-v2

Changes since v1:
https://lore.kernel.org/live-patching/20250127213310.2496133-1-wnliu@google.com/

 - Fixed detection of sframe support in compiler (Josh, Jens)
 - Adapt latest sframe v2 header definition from userspace patch series
   (Josh)
 - Folded together unwinder/stacktrace patches (Prasanna)
 - Fix "orphan section" warnings for .init.sframe sections (Puranjay,
   Indu, Josh)
 - Build VDSO without sframe (Dylan)
 - Added support for modules (Weinan)

Dylan Hatch (2):
  unwind: build kernel with sframe info
  unwind: add sframe v2 header

Weinan Liu (4):
  arm64: entry: add unwind info for various kernel entries
  unwind: Implement generic sframe unwinder library
  arm64/module, unwind: Add sframe support for modules.
  unwind: arm64: Add reliable stacktrace with sframe unwinder.

 Makefile                                   |   8 +
 arch/Kconfig                               |   6 +
 arch/arm64/Kconfig.debug                   |  10 +
 arch/arm64/include/asm/module.h            |   6 +
 arch/arm64/include/asm/stacktrace/common.h |   6 +
 arch/arm64/kernel/entry.S                  |  10 +
 arch/arm64/kernel/module.c                 |   5 +
 arch/arm64/kernel/setup.c                  |   2 +
 arch/arm64/kernel/stacktrace.c             | 102 +++++++++
 arch/arm64/kernel/vdso/Makefile            |   2 +-
 include/asm-generic/vmlinux.lds.h          |  15 ++
 include/linux/sframe_lookup.h              |  45 ++++
 kernel/Makefile                            |   1 +
 kernel/sframe.h                            |  75 +++++++
 kernel/sframe_lookup.c                     | 232 +++++++++++++++++++++
 15 files changed, 524 insertions(+), 1 deletion(-)
 create mode 100644 include/linux/sframe_lookup.h
 create mode 100644 kernel/sframe.h
 create mode 100644 kernel/sframe_lookup.c

-- 
2.51.0.355.g5224444f11-goog
Re: [PATCH v2 0/6] unwind, arm64: add sframe unwinder for kernel
Posted by Song Liu 3 days, 8 hours ago 
On Thu, Sep 4, 2025 at 3:39 PM Dylan Hatch <dylanbhatch@google.com> 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 proposals
> could integrate common functionality in the future.
>
> Currently, only GCC supports sframe.
>
> These patches are based on v6.17-rc4 and are available on github [3].
>
> Ref:
> [1]: https://sourceware.org/binutils/docs/sframe-spec.html
> [2]: https://lore.kernel.org/lkml/cover.1730150953.git.jpoimboe@kernel.org/
> [3]: https://github.com/dylanbhatch/linux/tree/sframe-v2

I run the following test on this sframe-v2 branch:

bpftrace -e 'kprobe:security_file_open {printf("%s",
kstack);@count+=1; if (@count > 1) {exit();}}'

        security_file_open+0
        bpf_prog_eaca355a0dcdca7f_kprobe_security_file_open_1+16641632@./bpftrace.bpf.o:0
        path_openat+1892
        do_filp_open+132
        do_open_execat+84
        alloc_bprm+44
        do_execveat_common.isra.0+116
        __arm64_sys_execve+72
        invoke_syscall+76
        el0_svc_common.constprop.0+68
        do_el0_svc+32
        el0_svc+56
        el0t_64_sync_handler+152
        el0t_64_sync+388

This looks wrong. The right call trace should be:

  do_filp_open
    => path_openat
      => vfs_open
        => do_dentry_open
          => security_file_open
            => bpf_prog_eaca355a0dcdca7f_...

I am not sure whether this is just a problem with the bpf program,
or also with something else.

Thanks,
Song
Re: [PATCH v2 0/6] unwind, arm64: add sframe unwinder for kernel
Posted by Puranjay Mohan 3 days, 8 hours ago 
On Mon, Sep 29, 2025 at 9:46 PM Song Liu <song@kernel.org> wrote:
>
> On Thu, Sep 4, 2025 at 3:39 PM Dylan Hatch <dylanbhatch@google.com> 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 proposals
> > could integrate common functionality in the future.
> >
> > Currently, only GCC supports sframe.
> >
> > These patches are based on v6.17-rc4 and are available on github [3].
> >
> > Ref:
> > [1]: https://sourceware.org/binutils/docs/sframe-spec.html
> > [2]: https://lore.kernel.org/lkml/cover.1730150953.git.jpoimboe@kernel.org/
> > [3]: https://github.com/dylanbhatch/linux/tree/sframe-v2
>
> I run the following test on this sframe-v2 branch:
>
> bpftrace -e 'kprobe:security_file_open {printf("%s",
> kstack);@count+=1; if (@count > 1) {exit();}}'
>
>         security_file_open+0
>         bpf_prog_eaca355a0dcdca7f_kprobe_security_file_open_1+16641632@./bpftrace.bpf.o:0
>         path_openat+1892
>         do_filp_open+132
>         do_open_execat+84
>         alloc_bprm+44
>         do_execveat_common.isra.0+116
>         __arm64_sys_execve+72
>         invoke_syscall+76
>         el0_svc_common.constprop.0+68
>         do_el0_svc+32
>         el0_svc+56
>         el0t_64_sync_handler+152
>         el0t_64_sync+388
>
> This looks wrong. The right call trace should be:
>
>   do_filp_open
>     => path_openat
>       => vfs_open
>         => do_dentry_open
>           => security_file_open
>             => bpf_prog_eaca355a0dcdca7f_...
>
> I am not sure whether this is just a problem with the bpf program,
> or also with something else.

I will try to debug this more but am just curious about BPF's
interactions with sframe.
The sframe data for bpf programs doesn't exist, so we would need to
add that support
and that wouldn't be trivial, given the BPF programs are JITed.

Thanks,
Puranjay

Patchew 2.1-devel-b67e4c2

© 2016 - 2025 Red Hat, Inc.