by Ian Rogers

[permalink] [raw]

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

On Thu, Mar 30, 2023 at 9:50 AM Ian Rogers <[email protected]> wrote:
>
> On Thu, Mar 30, 2023 at 7:08 AM James Clark <[email protected]> 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 <[email protected]>
> > > ---
> > > 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/[email protected]/
> 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

Sorry to say I couldn't repro on Debian:

$ make ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- -C tools/perf
NO_LIBELF=1 NO_LIBTRACEEVENT=1
make: Entering directory '/home/irogers/kernel.org/tools/perf'
BUILD: Doing 'make -j16' parallel build
Warning: Kernel ABI header at 'tools/include/uapi/linux/in.h' differs
from latest version at 'include/uapi/linux/in.h'
diff -u tools/include/uapi/linux/in.h include/uapi/linux/in.h
Warning: Kernel ABI header at
'tools/arch/x86/include/asm/cpufeatures.h' differs from latest version
at 'arch/x86/include/asm/cpufeatures.h'
diff -u tools/arch/x86/include/asm/cpufeatures.h
arch/x86/include/asm/cpufeatures.h
Warning: Kernel ABI header at
'tools/arch/arm64/include/uapi/asm/perf_regs.h' differs from latest
version at 'arch/arm64/include/uapi/asm/perf_regs.h'
diff -u tools/arch/arm64/include/uapi/asm/perf_regs.h
arch/arm64/include/uapi/asm/perf_regs.h
Warning: Kernel ABI header at 'tools/include/linux/coresight-pmu.h'
differs from latest version at 'include/linux/coresight-pmu.h'
diff -u tools/include/linux/coresight-pmu.h include/linux/coresight-pmu.h
Makefile.config:588: No sys/sdt.h found, no SDT events are defined,
please install systemtap-sdt-devel or systemtap-sdt-dev
Makefile.config:679: Disabling post unwind, no support found.
Makefile.config:747: No libcrypto.h found, disables jitted code
injection, please install openssl-devel or libssl-dev
Makefile.config:759: slang not found, disables TUI support. Please
install slang-devel, libslang-devor libslang2-dev
Makefile.config:806: Missing perl devel files. Disabling perl
scripting support, please install perl-ExtUtils-Embed/libperl-dev
Makefile.config:846: No 'Python.h' was found: disables Python support
- please install python-devel/python-dev
Makefile.config:951: No liblzma found, disables xz kernel module
decompression, please install xz-devel/liblzma-dev
Makefile.config:964: No libzstd found, disables trace compression,
please install libzstd-dev[el] and/or set LIBZSTD_DIR
Makefile.config:975: No libcap found, disables capability support,
please install libcap-devel/libcap-dev
Makefile.config:988: No numa.h found, disables 'perf bench numa mem'
benchmark, please install numactl-devel/libnuma-devel/libnuma-dev
Makefile.config:1047: No libbabeltrace found, disables 'perf data' CTF
format support, please install
libbabeltrace-dev[el]/libbabeltrace-ctf-dev
Makefile.config:1138: libpfm4 not found, disables libpfm4 support.
Please install libpfm4-dev

Auto-detecting system features:
... dwarf: [ OFF ]
... dwarf_getlocations: [ OFF ]
... glibc: [ on ]
... libbfd: [ OFF ]
... libbfd-buildid: [ OFF ]
... libcap: [ OFF ]
... libelf: [ OFF ]
... libnuma: [ OFF ]
... numa_num_possible_cpus: [ OFF ]
... libperl: [ OFF ]
... libpython: [ OFF ]
... libcrypto: [ OFF ]
... libunwind: [ OFF ]
... libdw-dwarf-unwind: [ OFF ]
... zlib: [ OFF ]
... lzma: [ OFF ]
... get_cpuid: [ OFF ]
... bpf: [ on ]
... libaio: [ on ]
... libzstd: [ OFF ]

INSTALL libsubcmd_headers
INSTALL libsymbol_headers
INSTALL libapi_headers
INSTALL libperf_headers
FLEX util/parse-events-flex.c
FLEX util/pmu-flex.c
CC util/pmu-bison.o
FLEX util/expr-flex.c
CC util/expr-bison.o
CXX util/demangle-cxx.o
CC util/demangle-ocaml.o
CC util/demangle-java.o
CC util/demangle-rust.o
CC util/perf-hooks.o
CC util/parse-events.o
CC util/parse-events-flex.o
CC util/pmu.o
CC util/pmu-flex.o
CC util/expr-flex.o
CC util/expr.o
LD util/perf-in.o
LD perf-in.o
LINK perf
make: Leaving directory '.../tools/perf'

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) {

2023-03-31 09:30:36

by James Clark

[permalink] [raw]

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

On 30/03/2023 20:03, Ian Rogers wrote:
> On Thu, Mar 30, 2023 at 9:50 AM Ian Rogers <[email protected]> wrote:
>>
>> On Thu, Mar 30, 2023 at 7:08 AM James Clark <[email protected]> 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 <[email protected]>
>>>> ---
>>>> 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/[email protected]/
>> 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
>
> Sorry to say I couldn't repro on Debian:
>
> $ make ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- -C tools/perf
> NO_LIBELF=1 NO_LIBTRACEEVENT=1

If you have NO_LIBELF=1 it sets NO_DEMANGLE=1 automatically so it skips
the c++ linking step. If you run with V=1 you can see that it doesn't
have -lstdc++ on the last link line.

But, having said that, I went to make a full reproducer in docker but it
actually worked. Turns out that the issue was on my end. I'd used
update-alternatives for a different compiler version and looks like I
had half of one gcc and half of another g++. Completely my fault, sorry
for the noise!

James