libcamera: base: backtrace: Use libdw to provide symbolic names

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@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

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);

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