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    SubjectRe: [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@google.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@google.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
    >

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