Re: [PATCH v1 09/13] perf symbol: Add abi::__cxa_demangle C++ demangling support

From: Ian Rogers
Date: Thu Mar 30 2023 - 12:51:21 EST

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In reply to: James Clark: "Re: [PATCH v1 09/13] perf symbol: Add abi::__cxa_demangle C++ demangling support"
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On Thu, Mar 30, 2023 at 7:08 AM James Clark <james.clark@xxxxxxx> wrote:
>
>
>
> On 11/03/2023 06:57, Ian Rogers wrote:
> > Refactor C++ demangling out of symbol-elf into its own files similar
> > to other languages. Add abi::__cxa_demangle support. As the other
> > demanglers are not shippable with distributions, this brings back C++
> > demangling in a common case. It isn't perfect as the support for
> > optionally demangling arguments and modifiers isn't present.
> >
> > Signed-off-by: Ian Rogers <irogers@xxxxxxxxxx>
> > ---
> > tools/perf/Makefile.config | 29 +++++++++---------
> > tools/perf/util/Build | 1 +
> > tools/perf/util/demangle-cxx.cpp | 50 ++++++++++++++++++++++++++++++++
> > tools/perf/util/demangle-cxx.h | 16 ++++++++++
> > tools/perf/util/symbol-elf.c | 37 +++++------------------
> > 5 files changed, 88 insertions(+), 45 deletions(-)
> > create mode 100644 tools/perf/util/demangle-cxx.cpp
> > create mode 100644 tools/perf/util/demangle-cxx.h
> >
> > diff --git a/tools/perf/Makefile.config b/tools/perf/Makefile.config
> > index 5756498248e0..fdeca45cf15f 100644
> > --- a/tools/perf/Makefile.config
> > +++ b/tools/perf/Makefile.config
> > @@ -906,6 +906,7 @@ ifdef BUILD_NONDISTRO
> > endif
> >
> > CFLAGS += -DHAVE_LIBBFD_SUPPORT
> > + CXXFLAGS += -DHAVE_LIBBFD_SUPPORT
> > ifeq ($(feature-libbfd-buildid), 1)
> > CFLAGS += -DHAVE_LIBBFD_BUILDID_SUPPORT
> > else
> > @@ -913,26 +914,24 @@ ifdef BUILD_NONDISTRO
> > endif
> > endif
> >
> > -ifdef NO_DEMANGLE
> > - CFLAGS += -DNO_DEMANGLE
> > -else
> > +ifndef NO_DEMANGLE
> > + $(call feature_check,cxa-demangle)
> > + ifeq ($(feature-cxa-demangle), 1)
> > + EXTLIBS += -lstdc++
>
> Hi Ian,
>
> I think cross compilation for arm on x86 isn't working after this change
> (at least on Ubuntu).
>
> Even with all of the arm64 libstdc++ stuff installed, you can only link
> to it using g++, but the perf build tries to link to it using gcc. Not
> sure it's some quirk with the search paths on Ubuntu or something else:
>
> $ aarch64-linux-gnu-gcc -lstdc++
>
> /usr/lib/gcc-cross/aarch64-linux-gnu/12/../../../../aarch64-linux-
> gnu/bin/ld: cannot find -lstdc++: No such file or directory
> collect2: error: ld returned 1 exit status
>
> g++ gets further:
>
> $ aarch64-linux-gnu-g++ -lstdc++
>
> ...
> (.text+0x20): undefined reference to `main'
> collect2: error: ld returned 1 exit status
>
> At the end of the perf build it looks like something similar is
> happening (with all the non interesting bits deleted):
>
> $ make ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- -C tools/perf
> NO_BPF_SKEL=1 V=1
>
> aarch64-linux-gnu-gcc ... -o perf
>
> /usr/lib/gcc-cross/aarch64-linux-gnu/12/../../../../aarch64-linux-gnu/bin/ld:
> cannot find -lstdc++: No such file or directory
>
> If I build with NO_DEMANGLE=1 then the build works, but I think it would
> at be best to autodetect rather than have to do this. Or maybe even link
> at the end with g++ if we're going to use libstdc++?

Hi James,

sorry for the problems you are having, I'll see if I can get a repo. I
did add a feature test with this change in the same set:
https://lore.kernel.org/lkml/20230311065753.3012826-9-irogers@xxxxxxxxxx/
So it should be feature testing and only enabling when
HAVE_CXA_DEMANGLE_SUPPORT is present. Obviously something is up, so
I'll have a think about it.

Thanks,
Ian

> Thanks
> James
>
> > + CFLAGS += -DHAVE_CXA_DEMANGLE_SUPPORT
> > + CXXFLAGS += -DHAVE_CXA_DEMANGLE_SUPPORT
> > + endif
> > ifdef BUILD_NONDISTRO
> > ifeq ($(filter -liberty,$(EXTLIBS)),)
> > - ifdef HAVE_CPLUS_DEMANGLE_SUPPORT
> > + $(call feature_check,cplus-demangle)
> > + ifeq ($(feature-cplus-demangle), 1)
> > EXTLIBS += -liberty
> > - else
> > - $(call feature_check,cplus-demangle)
> > - ifeq ($(feature-cplus-demangle), 1)
> > - EXTLIBS += -liberty
> > - endif
> > endif
> > endif
> > - endif
> > -
> > - ifneq ($(filter -liberty,$(EXTLIBS)),)
> > - CFLAGS += -DHAVE_CPLUS_DEMANGLE_SUPPORT
> > - else
> > - CFLAGS += -DNO_DEMANGLE
> > + ifneq ($(filter -liberty,$(EXTLIBS)),)
> > + CFLAGS += -DHAVE_CPLUS_DEMANGLE_SUPPORT
> > + CXXFLAGS += -DHAVE_CPLUS_DEMANGLE_SUPPORT
> > + endif
> > endif
> > endif
> >
> > diff --git a/tools/perf/util/Build b/tools/perf/util/Build
> > index 918b501f9bd8..8607575183a9 100644
> > --- a/tools/perf/util/Build
> > +++ b/tools/perf/util/Build
> > @@ -211,6 +211,7 @@ perf-$(CONFIG_ZSTD) += zstd.o
> >
> > perf-$(CONFIG_LIBCAP) += cap.o
> >
> > +perf-y += demangle-cxx.o
> > perf-y += demangle-ocaml.o
> > perf-y += demangle-java.o
> > perf-y += demangle-rust.o
> > diff --git a/tools/perf/util/demangle-cxx.cpp b/tools/perf/util/demangle-cxx.cpp
> > new file mode 100644
> > index 000000000000..8708bcafd370
> > --- /dev/null
> > +++ b/tools/perf/util/demangle-cxx.cpp
> > @@ -0,0 +1,50 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +#include "demangle-cxx.h"
> > +#include <stdlib.h>
> > +#include <string.h>
> > +#include <linux/compiler.h>
> > +
> > +#ifdef HAVE_LIBBFD_SUPPORT
> > +#define PACKAGE 'perf'
> > +#include <bfd.h>
> > +#endif
> > +
> > +#ifdef HAVE_CXA_DEMANGLE_SUPPORT
> > +#include <cxxabi.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
> > +
> > +/*
> > + * Demangle C++ function signature
> > + *
> > + * Note: caller is responsible for freeing demangled string
> > + */
> > +extern "C"
> > +char *cxx_demangle_sym(const char *str, 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);
> > +#elif defined(HAVE_CXA_DEMANGLE_SUPPORT)
> > + size_t len = strlen(str);
> > + char *output = (char*)malloc(len);
> > + int status;
> > +
> > + output = abi::__cxa_demangle(str, output, &len, &status);
> > + return output;
> > +#else
> > + return NULL;
> > +#endif
> > +}
> > diff --git a/tools/perf/util/demangle-cxx.h b/tools/perf/util/demangle-cxx.h
> > new file mode 100644
> > index 000000000000..26b5b66c0b4e
> > --- /dev/null
> > +++ b/tools/perf/util/demangle-cxx.h
> > @@ -0,0 +1,16 @@
> > +/* SPDX-License-Identifier: GPL-2.0 */
> > +#ifndef __PERF_DEMANGLE_CXX
> > +#define __PERF_DEMANGLE_CXX 1
> > +
> > +#ifdef __cplusplus
> > +extern "C" {
> > +#endif
> > +
> > +char *cxx_demangle_sym(const char *str, bool params, bool modifiers);
> > +
> > +#ifdef __cplusplus
> > +}
> > +#endif
> > +
> > +
> > +#endif /* __PERF_DEMANGLE_CXX */
> > diff --git a/tools/perf/util/symbol-elf.c b/tools/perf/util/symbol-elf.c
> > index 41882ae8452e..c0a2de42c51b 100644
> > --- a/tools/perf/util/symbol-elf.c
> > +++ b/tools/perf/util/symbol-elf.c
> > @@ -12,6 +12,7 @@
> > #include "maps.h"
> > #include "symbol.h"
> > #include "symsrc.h"
> > +#include "demangle-cxx.h"
> > #include "demangle-ocaml.h"
> > #include "demangle-java.h"
> > #include "demangle-rust.h"
> > @@ -25,6 +26,11 @@
> > #include <symbol/kallsyms.h>
> > #include <internal/lib.h>
> >
> > +#ifdef HAVE_LIBBFD_SUPPORT
> > +#define PACKAGE 'perf'
> > +#include <bfd.h>
> > +#endif
> > +
> > #ifndef EM_AARCH64
> > #define EM_AARCH64 183 /* ARM 64 bit */
> > #endif
> > @@ -45,34 +51,6 @@
> >
> > typedef Elf64_Nhdr GElf_Nhdr;
> >
> > -#ifndef DMGL_PARAMS
> > -#define DMGL_NO_OPTS 0 /* For readability... */
> > -#define DMGL_PARAMS (1 << 0) /* Include function args */
> > -#define DMGL_ANSI (1 << 1) /* Include const, volatile, etc */
> > -#endif
> > -
> > -#ifdef HAVE_LIBBFD_SUPPORT
> > -#define PACKAGE 'perf'
> > -#include <bfd.h>
> > -#else
> > -#ifdef HAVE_CPLUS_DEMANGLE_SUPPORT
> > -extern char *cplus_demangle(const char *, int);
> > -
> > -static inline char *bfd_demangle(void __maybe_unused *v, const char *c, int i)
> > -{
> > - return cplus_demangle(c, i);
> > -}
> > -#else
> > -#ifdef NO_DEMANGLE
> > -static inline char *bfd_demangle(void __maybe_unused *v,
> > - const char __maybe_unused *c,
> > - int __maybe_unused i)
> > -{
> > - return NULL;
> > -}
> > -#endif
> > -#endif
> > -#endif
> >
> > #ifndef HAVE_ELF_GETPHDRNUM_SUPPORT
> > static int elf_getphdrnum(Elf *elf, size_t *dst)
> > @@ -295,7 +273,6 @@ static bool want_demangle(bool is_kernel_sym)
> >
> > static char *demangle_sym(struct dso *dso, int kmodule, const char *elf_name)
> > {
> > - int demangle_flags = verbose > 0 ? (DMGL_PARAMS | DMGL_ANSI) : DMGL_NO_OPTS;
> > char *demangled = NULL;
> >
> > /*
> > @@ -306,7 +283,7 @@ static char *demangle_sym(struct dso *dso, int kmodule, const char *elf_name)
> > if (!want_demangle(dso->kernel || kmodule))
> > return demangled;
> >
> > - demangled = bfd_demangle(NULL, elf_name, demangle_flags);
> > + demangled = cxx_demangle_sym(elf_name, verbose > 0, verbose > 0);
> > if (demangled == NULL) {
> > demangled = ocaml_demangle_sym(elf_name);
> > if (demangled == NULL) {

Next message: Vladimir Oltean: "Re: [PATCH net-next 1/2] net: dsa: rzn1-a5psw: enable DPBU for CPU port and fix STP states"
Previous message: Yangtao Li: "[PATCH v2] f2fs: merge lz4hc_compress_pages() to lz4_compress_pages()"
In reply to: James Clark: "Re: [PATCH v1 09/13] perf symbol: Add abi::__cxa_demangle C++ demangling support"
Next in thread: Ian Rogers: "Re: [PATCH v1 09/13] perf symbol: Add abi::__cxa_demangle C++ demangling support"
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