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/* 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
#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
* \brief Generate call stack backtraces
*/
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
*
* 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 to 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_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);
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 */
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