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

Namhyung Kim
2026-03-26T22:51:22Z

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
>