[libcamera-devel] [PATCH v1 1/4] libcamera: base: Add Backtrace class
Laurent Pinchart
laurent.pinchart at ideasonboard.com
Fri Sep 24 12:23:20 CEST 2021
Create a new class to abstract generation and access to call stack
backtraces. The current implementation depends on the glibc backtrace()
implementation and is copied from the logger. Future development will
bring support for libunwind, transparently for the users of the class.
The logger backtrace implementation is dropped, replaced by usage of the
new Backtrace class.
Signed-off-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
---
include/libcamera/base/backtrace.h | 34 +++++++++
include/libcamera/base/meson.build | 1 +
meson.build | 4 --
src/libcamera/base/backtrace.cpp | 107 +++++++++++++++++++++++++++++
src/libcamera/base/log.cpp | 25 ++-----
src/libcamera/base/meson.build | 5 ++
6 files changed, 153 insertions(+), 23 deletions(-)
create mode 100644 include/libcamera/base/backtrace.h
create mode 100644 src/libcamera/base/backtrace.cpp
diff --git a/include/libcamera/base/backtrace.h b/include/libcamera/base/backtrace.h
new file mode 100644
index 000000000000..aefc76defa83
--- /dev/null
+++ b/include/libcamera/base/backtrace.h
@@ -0,0 +1,34 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+/*
+ * Copyright (C) 2021, Ideas on Board Oy
+ *
+ * backtrace.h - Call stack backtraces
+ */
+#ifndef __LIBCAMERA_BASE_BACKTRACE_H__
+#define __LIBCAMERA_BASE_BACKTRACE_H__
+
+#include <string>
+#include <vector>
+
+#include <libcamera/base/private.h>
+
+#include <libcamera/base/class.h>
+
+namespace libcamera {
+
+class Backtrace
+{
+public:
+ Backtrace();
+
+ std::string toString(unsigned int skipLevels = 0) const;
+
+private:
+ LIBCAMERA_DISABLE_COPY(Backtrace)
+
+ std::vector<void *> backtrace_;
+};
+
+} /* namespace libcamera */
+
+#endif /* __LIBCAMERA_BASE_BACKTRACE_H__ */
diff --git a/include/libcamera/base/meson.build b/include/libcamera/base/meson.build
index 9feb4b9346d5..525aba9d2919 100644
--- a/include/libcamera/base/meson.build
+++ b/include/libcamera/base/meson.build
@@ -3,6 +3,7 @@
libcamera_base_include_dir = libcamera_include_dir / 'base'
libcamera_base_headers = files([
+ 'backtrace.h',
'bound_method.h',
'class.h',
'event_dispatcher.h',
diff --git a/meson.build b/meson.build
index a49c484fe64e..dfed01ba26bc 100644
--- a/meson.build
+++ b/meson.build
@@ -29,10 +29,6 @@ cc = meson.get_compiler('c')
cxx = meson.get_compiler('cpp')
config_h = configuration_data()
-if cc.has_header_symbol('execinfo.h', 'backtrace')
- config_h.set('HAVE_BACKTRACE', 1)
-endif
-
if cc.has_header_symbol('unistd.h', 'issetugid')
config_h.set('HAVE_ISSETUGID', 1)
endif
diff --git a/src/libcamera/base/backtrace.cpp b/src/libcamera/base/backtrace.cpp
new file mode 100644
index 000000000000..913f7ba71b03
--- /dev/null
+++ b/src/libcamera/base/backtrace.cpp
@@ -0,0 +1,107 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+/*
+ * Copyright (C) 2021, Ideas on Board Oy
+ *
+ * backtrace.h - Call stack backtraces
+ */
+
+#include <libcamera/base/backtrace.h>
+
+#if HAVE_BACKTRACE
+#include <execinfo.h>
+#include <stdlib.h>
+#endif
+
+#include <sstream>
+
+#include <libcamera/base/span.h>
+
+/**
+ * \file backtrace.h
+ * \brief Generate call stack backtraces
+ */
+
+namespace libcamera {
+
+/**
+ * \class Backtrace
+ * \brief Representation of a call stack backtrace
+ *
+ * The Backtrace class represents a function call stack. Constructing an
+ * instance captures the call stack at the point the instance is constructed.
+ * The instance can later be used to access the call stack and generate a
+ * human-readable representation with the toString() function.
+ *
+ * Depending on the platform, different backends can be used to generate the
+ * backtrace. The Backtrace class provides a best effort to capture accurate
+ * backtraces, but doesn't offer any guarantee of a particular backtrace format.
+ */
+
+/**
+ * \brief Construct a backtrace
+ *
+ * The backtrace captures the call stack at the point where it is constructed.
+ * It can later be converted to a string with toString().
+ */
+Backtrace::Backtrace()
+{
+#if HAVE_BACKTRACE
+ backtrace_.resize(32);
+
+ int num_entries = backtrace(backtrace_.data(), backtrace_.size());
+ if (num_entries < 0) {
+ backtrace_.clear();
+ return;
+ }
+
+ backtrace_.resize(num_entries);
+#endif
+}
+
+/**
+ * \brief Convert a backtrace to a string representation
+ * \param[in] skipLevels Number of initial levels to skip in the backtrace
+ *
+ * The string representation of the backtrace is a multi-line string, with one
+ * line per call stack entry. The format of the entries isn't specified and is
+ * platform-dependent.
+ *
+ * The \a skipLevels parameter indicates how many initial entries to skip from
+ * the backtrace. This can be used to hide functions that wrap the construction
+ * of the Backtrace instance from the call stack. The Backtrace constructor
+ * itself is automatically skipped and never shown in the backtrace.
+ *
+ * If backtrace generation fails for any reason (usually because the platform
+ * doesn't support this feature), an empty string is returned.
+ *
+ * \return A string representation of the backtrace, or an empty string if
+ * backtrace generation isn't possible
+ */
+std::string Backtrace::toString(unsigned int skipLevels) const
+{
+ /* Skip the first entry, corresponding to the Backtrace construction. */
+ skipLevels += 1;
+
+ if (backtrace_.size() <= skipLevels)
+ return std::string();
+
+#if HAVE_BACKTRACE
+ Span<void *const> trace{ backtrace_ };
+ trace = trace.subspan(skipLevels);
+
+ char **strings = backtrace_symbols(trace.data(), trace.size());
+ if (strings) {
+ std::ostringstream msg;
+
+ for (unsigned int i = 0; i < trace.size(); ++i)
+ msg << strings[i] << std::endl;
+
+ free(strings);
+ return msg.str();
+ }
+#endif
+
+ return std::string();
+}
+
+} /* namespace libcamera */
diff --git a/src/libcamera/base/log.cpp b/src/libcamera/base/log.cpp
index a3e3f9ea2712..272c440589d4 100644
--- a/src/libcamera/base/log.cpp
+++ b/src/libcamera/base/log.cpp
@@ -8,9 +8,6 @@
#include <libcamera/base/log.h>
#include <array>
-#if HAVE_BACKTRACE
-#include <execinfo.h>
-#endif
#include <fstream>
#include <iostream>
#include <list>
@@ -23,6 +20,7 @@
#include <libcamera/logging.h>
+#include <libcamera/base/backtrace.h>
#include <libcamera/base/thread.h>
#include <libcamera/base/utils.h>
@@ -418,31 +416,20 @@ void Logger::write(const LogMessage &msg)
*/
void Logger::backtrace()
{
-#if HAVE_BACKTRACE
std::shared_ptr<LogOutput> output = std::atomic_load(&output_);
if (!output)
return;
- void *buffer[32];
- int num_entries = ::backtrace(buffer, std::size(buffer));
- char **strings = backtrace_symbols(buffer, num_entries);
- if (!strings)
- return;
-
- std::ostringstream msg;
- msg << "Backtrace:" << std::endl;
-
/*
* Skip the first two entries that correspond to this function and
* ~LogMessage().
*/
- for (int i = 2; i < num_entries; ++i)
- msg << strings[i] << std::endl;
+ std::string backtrace = Backtrace().toString(2);
+ if (backtrace.empty())
+ return;
- output->write(msg.str());
-
- free(strings);
-#endif
+ output->write("Backtrace:\n");
+ output->write(backtrace);
}
/**
diff --git a/src/libcamera/base/meson.build b/src/libcamera/base/meson.build
index 8e125744d823..85af01a19365 100644
--- a/src/libcamera/base/meson.build
+++ b/src/libcamera/base/meson.build
@@ -1,6 +1,7 @@
# SPDX-License-Identifier: CC0-1.0
libcamera_base_sources = files([
+ 'backtrace.cpp',
'class.cpp',
'bound_method.cpp',
'event_dispatcher.cpp',
@@ -18,6 +19,10 @@ libcamera_base_sources = files([
'utils.cpp',
])
+if cc.has_header_symbol('execinfo.h', 'backtrace')
+ config_h.set('HAVE_BACKTRACE', 1)
+endif
+
libcamera_base_deps = [
dependency('threads'),
libatomic,
--
Regards,
Laurent Pinchart
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