Re: Can perf drop libunwind support

[Masami Hiramatsu (Google) <mhiramat@kernel.org>]

On Wed, 23 Oct 2024 14:57:05 -0700
Ian Rogers <irogers@google.com> wrote:

> Hi,
> 
> perf wants to build with BPF support these days. libbpf has a
> dependency on libelf, part of elfutils. libdw is also part of elfutils
> and amongst other things provides unwinding support. My understanding
> is libdw unwinding is used by perf in preference to libunwind when
> present. My suspicion is that libunwind is being feature tested,
> linked against but then seldom or never used. Given this could perf
> drop libunwind support in order to simplify the code base?

libunwind focuses on unwinding but libdw (elfutils-dev) is more general,
so if we can unwind only with libdw, we can remove libunwind dependency.

Here my concern is that the libunwind is smaller than libdw, thus
any small system may still need libunwind support. Can we warn when
using libunwind at this point? After all users move to libdw we
can safely remove it.

Thank you,

> 
> Possible savings:
>  - remove libunwind's 8 feature tests
>  - removal of 10 arch or not libunwind C files in perf
>  - removal of libunwind #ifdef-ed code throughout common files.
> 
> Thanks,
> Ian


-- 
Masami Hiramatsu (Google) <mhiramat@kernel.org>