[libcamera-devel] [PATCH v1 2/4] libcamera: base: backtrace: Use libdw to provide symbolic names
Laurent Pinchart
laurent.pinchart at ideasonboard.com
Fri Sep 24 12:23:21 CEST 2021
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);
+ entry << (name ? name : symbol) << "+0x" << std::hex << offset
+ << std::dec;
+ free(name);
+ } 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
--
Regards,
Laurent Pinchart
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