linux-kernel - Re: [PATCH v1] perf build: Don't compile demangle-cxx.cpp if not necessary

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Message-ID: <CAP-5=fXuKqU=ZD4G3t1H=dD1SMghiVXHj5YTFhX+Jj98jAiVUg@mail.gmail.com>
Date:   Wed, 26 Apr 2023 22:27:42 -0700
From:   Ian Rogers <irogers@...gle.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Ian Rogers <irogers@...gle.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Ravi Bangoria <ravi.bangoria@....com>,
        Qi Liu <liuqi115@...wei.com>, Leo Yan <leo.yan@...aro.org>,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] perf build: Don't compile demangle-cxx.cpp if not necessary

On Mon, Apr 17, 2023 at 12:25 PM Ian Rogers <irogers@...gle.com> wrote:
>
> demangle-cxx.cpp requires a C++ compiler, but feature checks may fail
> because of the absence of this. Add a CONFIG_CXX_DEMANGLE so that the
> source isn't built if not supported. Copy libbfd and cplus demangle
> variants to a weak symbol-elf.c version so they aren't dependent on
> C++. These variants are only built with the build option
> BUILD_NONDISTRO=1.
>
> Signed-off-by: Ian Rogers <irogers@...gle.com>

Testing on arm and noticed we hadn't picked this one up.

Thanks,
Ian

> ---
>  tools/perf/Makefile.config   |  1 +
>  tools/perf/util/Build        |  2 +-
>  tools/perf/util/symbol-elf.c | 27 +++++++++++++++++++++++++++
>  3 files changed, 29 insertions(+), 1 deletion(-)
>
> diff --git a/tools/perf/Makefile.config b/tools/perf/Makefile.config
> index 71442c54c25f..5f0f24b56f50 100644
> --- a/tools/perf/Makefile.config
> +++ b/tools/perf/Makefile.config
> @@ -923,6 +923,7 @@ ifndef NO_DEMANGLE
>      EXTLIBS += -lstdc++
>      CFLAGS += -DHAVE_CXA_DEMANGLE_SUPPORT
>      CXXFLAGS += -DHAVE_CXA_DEMANGLE_SUPPORT
> +    $(call detected,CONFIG_CXX_DEMANGLE)
>    endif
>    ifdef BUILD_NONDISTRO
>      ifeq ($(filter -liberty,$(EXTLIBS)),)
> diff --git a/tools/perf/util/Build b/tools/perf/util/Build
> index bd18fe5f2719..f9df1df1eec0 100644
> --- a/tools/perf/util/Build
> +++ b/tools/perf/util/Build
> @@ -214,7 +214,7 @@ perf-$(CONFIG_ZSTD) += zstd.o
>
>  perf-$(CONFIG_LIBCAP) += cap.o
>
> -perf-y += demangle-cxx.o
> +perf-$(CONFIG_CXX_DEMANGLE) += demangle-cxx.o
>  perf-y += demangle-ocaml.o
>  perf-y += demangle-java.o
>  perf-y += demangle-rust.o
> diff --git a/tools/perf/util/symbol-elf.c b/tools/perf/util/symbol-elf.c
> index 35724f6a84fa..cd08bdb9824f 100644
> --- a/tools/perf/util/symbol-elf.c
> +++ b/tools/perf/util/symbol-elf.c
> @@ -31,6 +31,13 @@
>  #include <bfd.h>
>  #endif
>
> +#if defined(HAVE_LIBBFD_SUPPORT) || defined(HAVE_CPLUS_DEMANGLE_SUPPORT)
> +#ifndef DMGL_PARAMS
> +#define DMGL_PARAMS     (1 << 0)  /* Include function args */
> +#define DMGL_ANSI       (1 << 1)  /* Include const, volatile, etc */
> +#endif
> +#endif
> +
>  #ifndef EM_AARCH64
>  #define EM_AARCH64     183  /* ARM 64 bit */
>  #endif
> @@ -271,6 +278,26 @@ static bool want_demangle(bool is_kernel_sym)
>         return is_kernel_sym ? symbol_conf.demangle_kernel : symbol_conf.demangle;
>  }
>
> +/*
> + * Demangle C++ function signature, typically replaced by demangle-cxx.cpp
> + * version.
> + */
> +__weak char *cxx_demangle_sym(const char *str __maybe_unused, bool params __maybe_unused,
> +                             bool modifiers __maybe_unused)
> +{
> +#ifdef HAVE_LIBBFD_SUPPORT
> +       int flags = (params ? DMGL_PARAMS : 0) | (modifiers ? DMGL_ANSI : 0);
> +
> +       return bfd_demangle(NULL, str, flags);
> +#elif defined(HAVE_CPLUS_DEMANGLE_SUPPORT)
> +       int flags = (params ? DMGL_PARAMS : 0) | (modifiers ? DMGL_ANSI : 0);
> +
> +       return cplus_demangle(str, flags);
> +#else
> +       return NULL;
> +#endif
> +}
> +
>  static char *demangle_sym(struct dso *dso, int kmodule, const char *elf_name)
>  {
>         char *demangled = NULL;
> --
> 2.40.0.634.g4ca3ef3211-goog
>