Re: [PATCH v1 0/2] perf build: Remove libunwind support

[Namhyung Kim <namhyung@kernel.org>]

On Sat, Mar 21, 2026 at 04:42:18PM -0700, Ian Rogers wrote:
> libunwind support exists for "--call-graph dwarf", however, libunwind
> support has been opt-in rather than opt-out since Linux v6.13 as libdw
> is preferred - commit 13e17c9ff49119aa ("perf build: Make libunwind
> opt-in rather than opt-out"). A problem with the libdw support was
> that it was slow, an issue fixed in Linux v7.0 in commit 6b2658b3f36a
> ("perf unwind-libdw: Don't discard loaded ELF/DWARF after every
> unwind"). As such libunwind support is now unnecessary.
> 
> The patch series:
> https://lore.kernel.org/lkml/20260305221927.3237145-1-irogers@google.com/
> looked to make the libunwind support in perf similar to the libdw
> support, allow cross-architecture unwinding, etc. This was motivated
> by the perf regs conventions being altered by the addition of x86 APX
> support:
> https://lore.kernel.org/lkml/20260209072047.2180332-1-dapeng1.mi@linux.intel.com/
> It is necessary to translate the library's notion of registers to the
> perf register convention so that the stack unwinding state can be
> initialized. On this series it was stated that removing libunwind
> support from perf should be an option, rather than updating support:
> https://lore.kernel.org/lkml/abxs-2rozL1tBEO1@google.com/
> This was also what motivated making libunwind opt-in rather than
> opt-out.
> 
> Given that 7 minor releases have happened with libunwind "deprecated"
> by making it opt-in, let's remove the libunwind support. There doesn't
> appear to be any disagreement to this on the mailing list.

I'm not sure if we want to remove it now.  I think we need more time to
verify libdw unwinding is stable and fast enough.  Also maybe we can
add build- or run-time warning when people try to use libunwind.

Thanks,
Namhyung

> 
> Ian Rogers (2):
>   perf build: Remove libunwind support
>   tools build: Remove libunwind feature tests
> 
>  tools/build/feature/Makefile                  |  31 -
>  tools/build/feature/test-libunwind-aarch64.c  |  27 -
>  tools/build/feature/test-libunwind-arm.c      |  28 -
>  .../test-libunwind-debug-frame-aarch64.c      |  17 -
>  .../feature/test-libunwind-debug-frame-arm.c  |  17 -
>  .../feature/test-libunwind-debug-frame.c      |  17 -
>  tools/build/feature/test-libunwind-x86.c      |  28 -
>  tools/build/feature/test-libunwind-x86_64.c   |  28 -
>  tools/build/feature/test-libunwind.c          |  28 -
>  tools/perf/Documentation/perf-check.txt       |   1 -
>  tools/perf/Documentation/perf-config.txt      |   4 +-
>  tools/perf/Documentation/perf-record.txt      |   2 +-
>  tools/perf/Makefile.config                    | 163 +---
>  tools/perf/Makefile.perf                      |   3 -
>  tools/perf/arch/arm/util/Build                |   1 -
>  tools/perf/arch/arm/util/unwind-libunwind.c   |  50 --
>  tools/perf/arch/arm64/util/Build              |   1 -
>  tools/perf/arch/arm64/util/unwind-libunwind.c |  17 -
>  tools/perf/arch/loongarch/util/Build          |   1 -
>  .../arch/loongarch/util/unwind-libunwind.c    |  82 --
>  tools/perf/arch/mips/util/Build               |   1 -
>  tools/perf/arch/mips/util/unwind-libunwind.c  |  22 -
>  tools/perf/arch/powerpc/util/Build            |   1 -
>  .../perf/arch/powerpc/util/unwind-libunwind.c |  92 --
>  tools/perf/arch/x86/util/Build                |   1 -
>  tools/perf/arch/x86/util/unwind-libunwind.c   | 115 ---
>  tools/perf/builtin-check.c                    |   1 -
>  tools/perf/builtin-report.c                   |   4 +-
>  tools/perf/tests/make                         |   2 -
>  tools/perf/util/Build                         |   5 -
>  tools/perf/util/callchain.c                   |   2 +-
>  tools/perf/util/dso.h                         |   6 -
>  tools/perf/util/libunwind/arm64.c             |  40 -
>  tools/perf/util/libunwind/x86_32.c            |  41 -
>  tools/perf/util/maps.c                        |  47 +-
>  tools/perf/util/maps.h                        |   6 -
>  tools/perf/util/thread.c                      |  40 +-
>  tools/perf/util/thread.h                      |   1 -
>  tools/perf/util/unwind-libunwind-local.c      | 832 ------------------
>  tools/perf/util/unwind-libunwind.c            |  92 --
>  tools/perf/util/unwind.h                      |  41 +-
>  41 files changed, 19 insertions(+), 1919 deletions(-)
>  delete mode 100644 tools/build/feature/test-libunwind-aarch64.c
>  delete mode 100644 tools/build/feature/test-libunwind-arm.c
>  delete mode 100644 tools/build/feature/test-libunwind-debug-frame-aarch64.c
>  delete mode 100644 tools/build/feature/test-libunwind-debug-frame-arm.c
>  delete mode 100644 tools/build/feature/test-libunwind-debug-frame.c
>  delete mode 100644 tools/build/feature/test-libunwind-x86.c
>  delete mode 100644 tools/build/feature/test-libunwind-x86_64.c
>  delete mode 100644 tools/build/feature/test-libunwind.c
>  delete mode 100644 tools/perf/arch/arm/util/unwind-libunwind.c
>  delete mode 100644 tools/perf/arch/arm64/util/unwind-libunwind.c
>  delete mode 100644 tools/perf/arch/loongarch/util/unwind-libunwind.c
>  delete mode 100644 tools/perf/arch/mips/util/unwind-libunwind.c
>  delete mode 100644 tools/perf/arch/powerpc/util/unwind-libunwind.c
>  delete mode 100644 tools/perf/arch/x86/util/unwind-libunwind.c
>  delete mode 100644 tools/perf/util/libunwind/arm64.c
>  delete mode 100644 tools/perf/util/libunwind/x86_32.c
>  delete mode 100644 tools/perf/util/unwind-libunwind-local.c
>  delete mode 100644 tools/perf/util/unwind-libunwind.c
> 
> -- 
> 2.53.0.959.g497ff81fa9-goog
>