[libcamera-devel] [PATCH v1 2/4] libcamera: base: backtrace: Use libdw to provide symbolic names
Nicolas Dufresne
nicolas at ndufresne.ca
Mon Sep 27 16:01:15 CEST 2021
Le vendredi 24 septembre 2021 à 13:23 +0300, Laurent Pinchart a écrit :
> libdw provides access to debugging information. This allows creating
> better stack trace entries, with file names and line numbers, but also
> with demangled symbols as the symbol name is available and can be passed
> to abi::__cxa_demangle().
>
> With libdw, the backtrace previously generated by backtrace_symbols()
>
> src/cam/../libcamera/libcamera.so(_ZN9libcamera14VimcCameraData4initEv+0xbd) [0x7f7dbb73222d]
> src/cam/../libcamera/libcamera.so(_ZN9libcamera19PipelineHandlerVimc5matchEPNS_16DeviceEnumeratorE+0x3e0) [0x7f7dbb731c40]
> src/cam/../libcamera/libcamera.so(_ZN9libcamera13CameraManager7Private22createPipelineHandlersEv+0x1a7) [0x7f7dbb5ea027]
> src/cam/../libcamera/libcamera.so(_ZN9libcamera13CameraManager7Private4initEv+0x98) [0x7f7dbb5e9dc8]
> src/cam/../libcamera/libcamera.so(_ZN9libcamera13CameraManager7Private3runEv+0x9f) [0x7f7dbb5e9c5f]
> src/cam/../libcamera/base/libcamera-base.so(_ZN9libcamera6Thread11startThreadEv+0xee) [0x7f7dbb3e95be]
> src/cam/../libcamera/base/libcamera-base.so(+0x4f9d7) [0x7f7dbb3ec9d7]
> src/cam/../libcamera/base/libcamera-base.so(+0x4f90e) [0x7f7dbb3ec90e]
> src/cam/../libcamera/base/libcamera-base.so(+0x4f2c2) [0x7f7dbb3ec2c2]
> /lib64/libpthread.so.0(+0x7e8e) [0x7f7dbab65e8e]
> /lib64/libc.so.6(clone+0x3f) [0x7f7dbb10b26f]
>
> becomes
>
> libcamera::VimcCameraData::init()+0xbd (src/libcamera/libcamera.so [0x00007f9de605b22d])
> libcamera::PipelineHandlerVimc::match(libcamera::DeviceEnumerator*)+0x3e0 (src/libcamera/libcamera.so [0x00007f9de605ac40])
> libcamera::CameraManager::Private::createPipelineHandlers()+0x1a7 (src/libcamera/libcamera.so [0x00007f9de5f13027])
> libcamera::CameraManager::Private::init()+0x98 (src/libcamera/libcamera.so [0x00007f9de5f12dc8])
> libcamera::CameraManager::Private::run()+0x9f (src/libcamera/libcamera.so [0x00007f9de5f12c5f])
> libcamera::Thread::startThread()+0xee (src/libcamera/base/libcamera-base.so [0x00007f9de5d125be])
> decltype(*(std::__1::forward<libcamera::Thread*>(fp0)).*fp()) std::__1::__invoke<void (libcamera::Thread::*)(), libcamera::Thread*, void>(void (libcamera::Thread::*&&)(), libcamera::Thread*&&)+0x77 (src/libcamera/base/libcamera-base.so [0x00007f9de5d159d7])
> void std::__1::__thread_execute<std::__1::unique_ptr<std::__1::__thread_struct, std::__1::default_delete<std::__1::__thread_struct> >, void (libcamera::Thread::*)(), libcamera::Thread*, 2ul>(std::__1::tuple<std::__1::unique_ptr<std::__1::__thread_struct, std::__1::default_delete<std::__1::__thread_struct> >, void (libcamera::Thread::*)(), libcamera::Thread*>&, std::__1::__tuple_indices<2ul>)+0x3e (src/libcamera/base/libcamera-base.so [0x00007f9de5d1590e])
> void* std::__1::__thread_proxy<std::__1::tuple<std::__1::unique_ptr<std::__1::__thread_struct, std::__1::default_delete<std::__1::__thread_struct> >, void (libcamera::Thread::*)(), libcamera::Thread*> >(void*)+0x62 (src/libcamera/base/libcamera-base.so [0x00007f9de5d152c2])
> start_thread+0xde (/var/tmp/portage/sys-libs/glibc-2.33-r1/work/glibc-2.33/nptl/pthread_create.c:482)
> __clone+0x3f (../sysdeps/unix/sysv/linux/x86_64/clone.S:97)
>
> The stack entries related to libcamera are missing source file name and
> line information, which will be investigated separately, but this is
> still an improvement.
>
> Use libdw when available, falling back to backtrace_symbols() otherwise,
> or if libdw fails for any reason.
>
> Signed-off-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
> ---
> src/libcamera/base/backtrace.cpp | 120 +++++++++++++++++++++++++++++++
> src/libcamera/base/meson.build | 7 ++
> 2 files changed, 127 insertions(+)
>
> diff --git a/src/libcamera/base/backtrace.cpp b/src/libcamera/base/backtrace.cpp
> index 913f7ba71b03..011f2e428d5d 100644
> --- a/src/libcamera/base/backtrace.cpp
> +++ b/src/libcamera/base/backtrace.cpp
> @@ -12,9 +12,16 @@
> #include <stdlib.h>
> #endif
>
> +#ifdef HAVE_DW
> +#include <cxxabi.h>
> +#include <elfutils/libdwfl.h>
> +#include <unistd.h>
> +#endif
> +
> #include <sstream>
>
> #include <libcamera/base/span.h>
> +#include <libcamera/base/utils.h>
>
> /**
> * \file backtrace.h
> @@ -23,6 +30,101 @@
>
> namespace libcamera {
>
> +namespace {
> +
> +#if HAVE_DW
> +class DwflParser
> +{
> +public:
> + DwflParser();
> + ~DwflParser();
> +
> + bool isValid() const { return valid_; }
> + std::string stackEntry(const void *ip);
> +
> +private:
> + Dwfl_Callbacks callbacks_;
> + Dwfl *dwfl_;
> + bool valid_;
> +};
> +
> +DwflParser::DwflParser()
> + : callbacks_({}), dwfl_(nullptr), valid_(false)
> +{
> + callbacks_.find_elf = dwfl_linux_proc_find_elf;
> + callbacks_.find_debuginfo = dwfl_standard_find_debuginfo;
> +
> + dwfl_ = dwfl_begin(&callbacks_);
> + if (!dwfl_)
> + return;
> +
> + int ret = dwfl_linux_proc_report(dwfl_, getpid());
> + if (ret)
> + return;
> +
> + ret = dwfl_report_end(dwfl_, nullptr, nullptr);
> + if (ret)
> + return;
> +
> + valid_ = true;
> +}
> +
> +DwflParser::~DwflParser()
> +{
> + if (dwfl_)
> + dwfl_end(dwfl_);
> +}
> +
> +std::string DwflParser::stackEntry(const void *ip)
> +{
> + Dwarf_Addr addr = reinterpret_cast<Dwarf_Addr>(ip);
> +
> + Dwfl_Module *module = dwfl_addrmodule(dwfl_, addr);
> + if (!module)
> + return std::string();
> +
> + std::ostringstream entry;
> +
> + GElf_Off offset;
> + GElf_Sym sym;
> + const char *symbol = dwfl_module_addrinfo(module, addr, &offset, &sym,
> + nullptr, nullptr, nullptr);
> + if (symbol) {
> + char *name = abi::__cxa_demangle(symbol, nullptr, nullptr, nullptr);
A suggestion, and yes, you have to choose between memory safety and ugly code.
std::unique_ptr<char[], decltype(free)*>{
abi::__cxa_demangle(symbol, nullptr, nullptr, nullptr),
free};
This is needed as by default C++ will assume that delete[] is to be used rather
then free.
> + entry << (name ? name : symbol) << "+0x" << std::hex << offset
> + << std::dec;
> + free(name);
And this error prone free is not longer needed, since you have a smart pointer.
> + } else {
> + entry << "??? [" << utils::hex(addr) << "]";
> + }
> +
> + entry << " (";
> +
> + Dwfl_Line *line = dwfl_module_getsrc(module, addr);
> + if (line) {
> + const char *filename;
> + int lineNumber = 0;
> +
> + filename = dwfl_lineinfo(line, &addr, &lineNumber, nullptr,
> + nullptr, nullptr);
> +
> + entry << (filename ? filename : "???") << ":" << lineNumber;
> + } else {
> + const char *filename = nullptr;
> +
> + dwfl_module_info(module, nullptr, nullptr, nullptr, nullptr,
> + nullptr, &filename, nullptr);
> +
> + entry << (filename ? filename : "???") << " [" << utils::hex(addr) << "]";
> + }
> +
> + entry << ")";
> + return entry.str();
> +}
> +#endif /* HAVE_DW */
> +
> +} /* namespace */
> +
> /**
> * \class Backtrace
> * \brief Representation of a call stack backtrace
> @@ -85,6 +187,24 @@ std::string Backtrace::toString(unsigned int skipLevels) const
> if (backtrace_.size() <= skipLevels)
> return std::string();
>
> +#if HAVE_DW
> + DwflParser dwfl;
> +
> + if (dwfl.isValid()) {
> + std::ostringstream msg;
> +
> + Span<void *const> trace{ backtrace_ };
> + for (const void *ip : trace.subspan(skipLevels)) {
> + if (ip)
> + msg << dwfl.stackEntry(ip) << std::endl;
> + else
> + msg << "???" << std::endl;
> + }
> +
> + return msg.str();
> + }
> +#endif
> +
> #if HAVE_BACKTRACE
> Span<void *const> trace{ backtrace_ };
> trace = trace.subspan(skipLevels);
> diff --git a/src/libcamera/base/meson.build b/src/libcamera/base/meson.build
> index 85af01a19365..1fa894cf1896 100644
> --- a/src/libcamera/base/meson.build
> +++ b/src/libcamera/base/meson.build
> @@ -19,13 +19,20 @@ libcamera_base_sources = files([
> 'utils.cpp',
> ])
>
> +libdw = cc.find_library('libdw', required : false)
> +
> if cc.has_header_symbol('execinfo.h', 'backtrace')
> config_h.set('HAVE_BACKTRACE', 1)
> endif
>
> +if libdw.found()
> + config_h.set('HAVE_DW', 1)
> +endif
> +
> libcamera_base_deps = [
> dependency('threads'),
> libatomic,
> + libdw,
> ]
>
> # Internal components must use the libcamera_base_private dependency to enable
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