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backtrace.hpp
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backtrace.hpp
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#ifndef __BACKTRACE_HPP_GUARD
#define __BACKTRACE_HPP_GUARD
// This file defines some utilities around glibc's backtrace() function to print
// a nice stack trace with code view and stuff. Requires glibc >= 2.1 and a
// POSIX system (uses popen(), addr2line from GNU binutils, and assumes POSIX
// path structure). Using any reasonably modern linux or BSD should work, MacOS
// with gcc+glibc might work, Windows will not work.
//
// The code is a bit of a spaghetti mess and the path parsing functions are
// criminally brittle.
//
// License: MIT
//
// Copyright 2020 Henrik Laxhuber
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
// SOFTWARE.
#include <cmath>
#include <cstdio>
#include <cstring>
#include <fstream>
#include <iomanip>
#include <iostream>
#include <map>
#include <ostream>
#include <sstream>
#include <stdexcept>
#include <string>
#ifndef _GNU_SOURCE
#define _GNU_SOURCE
#endif
#include <dlfcn.h> // we require glibc >= 2.0
#include <execinfo.h> // we require glibc >= 2.1
#include <link.h>
#include <unistd.h>
#if (not defined(__GLIBC__)) || __GLIBC__ < 2 || __GLIBC_MINOR__ < 1
#error backtrace requires glibc version 2.1 or greater. Using gcc on any modern linux system should work.
#endif
#if defined(WIN32) || defined(_WIN32) || defined(__WIN32__) || defined(__NT__)
#error Windows paths not supported
#endif
namespace _nice_backtrace_detail {
struct LineReader {
std::ifstream ifs;
std::map<size_t, size_t> lineoffsets;
size_t currline;
static constexpr size_t const LINE_GRANULARITY = 16;
struct eof_error : std::range_error {
template <class T>
explicit eof_error(T const &what) : std::range_error(what) {}
};
LineReader(std::string const &path)
: lineoffsets({{LINE_GRANULARITY + 1, 0}}), currline(1) {
ifs.open(path, std::ios::in);
if (ifs.fail()) {
std::stringstream ss;
ss << "Failed to open source file " << path;
throw std::invalid_argument(ss.str());
}
}
std::string read_line(size_t const linenr) {
std::string the_line;
if (linenr != currline) {
auto it = lineoffsets.upper_bound(linenr);
// it->second is offset to first element in lineoffsets where the linenr
// is _greater_ than the searched linenr. Since we store lineoffsets in
// the format {linenr+LINE_GRANULARITY, offset} (super hacky but it
// works...), this means we now can search forward for the line we want.
// note that lower_bound would not work here; this complexity is needed.
if (it != lineoffsets.end()) {
currline = it->first - LINE_GRANULARITY;
ifs.seekg(it->second, std::ios::beg);
} else {
auto rit = lineoffsets.rbegin();
currline = rit->first - LINE_GRANULARITY;
ifs.seekg(rit->second, std::ios::beg);
}
while (currline != linenr)
this->nextline(the_line);
}
this->nextline(the_line);
return the_line;
}
private:
void nextline(std::string &the_line) {
// std::cerr << "reading line " << currline << "; eofbit: " << ifs.eof()
// << "; failbit: " << ifs.fail() << "; goodbit: " << ifs.good()
// << std::endl;
std::getline(ifs, the_line);
if (ifs.eof()) {
ifs.clear();
throw eof_error("EOF reached");
}
if (ifs.fail())
throw std::runtime_error("read failed");
++currline;
if (currline % LINE_GRANULARITY == 1)
lineoffsets.emplace(currline + LINE_GRANULARITY, ifs.tellg());
}
};
static constexpr size_t const CONTEXT = 1;
void print_context(LineReader &linereader, unsigned char const nlinenrdigits,
size_t const err_linenr) {
for (size_t linenr = err_linenr > CONTEXT ? err_linenr - CONTEXT : 1;
linenr <= err_linenr + CONTEXT; ++linenr) {
try {
std::string the_line = linereader.read_line(linenr);
std::cerr << (linenr == err_linenr ? "\033[31;1m" : "\033[90m") << " "
<< std::setw(nlinenrdigits) << linenr << " │\033[0m "
<< the_line << std::endl;
} catch (LineReader::eof_error const &) {
break;
}
}
}
// don't ever do this please
std::string getline_from_fd(FILE *fd) {
std::string str;
char line[256];
parse_line: // yuck
if (std::fgets(line, sizeof(line), fd) == nullptr)
return str;
size_t linelen = std::strlen(line);
if (linelen == 255 && line[254] != '\n') {
// symbol longer than 255 chars
str += line;
goto parse_line;
}
line[linelen - 1] = '\0'; // remove EOL character
str += line;
return str;
}
// don't ever do this either
size_t split_path_filename(std::string const &path) {
size_t pos = path.rfind('/');
if (pos == std::string::npos)
return -1;
while (pos > 0 && path[pos - 1] == '\\')
pos = path.rfind('/', pos - 2);
return pos;
}
// this is also a brittle mess
std::string shorten_path(std::string const &path, std::string const &rel_to) {
size_t i = 0;
size_t same_pos = 0;
for (; i < std::min(path.length(), rel_to.length()); ++i) {
if (path[i] != rel_to[i])
break;
if (path[i] == '\\' && i + 1 < path.length() && i + 1 < rel_to.length() &&
path[i + 1] == '/' && rel_to[i + 1] == '/') {
++i;
continue;
}
if (path[i] == '/')
same_pos = i;
}
// same_pos now indexes first '/' after which both paths differ. If we
// matched all of rel_to, path might still have a trailing '/', so we might
// still need to match the last component in path:
if (i == rel_to.length() && i < path.length() && path[i] == '/') {
++i;
same_pos = i;
}
std::string relpath;
if (i < rel_to.length())
relpath += "../";
for (; i < rel_to.length(); ++i) {
if (i + 1 < rel_to.length() && rel_to[i] == '\\' && rel_to[i] == '/') {
++i;
continue;
}
if (rel_to[i] == '/')
relpath += "../";
}
if (relpath.length() > 0 && path[same_pos] == '/')
*relpath.rbegin() = '\0';
relpath += path.substr(same_pos);
if (relpath.length() < path.length())
return relpath;
else
return path;
}
// holds info about a single stack frame
struct Frameinfo {
const char *shared_obj; // might be null if all hell broke loose
std::string symbol; // .length() == 0 indicates unknown
std::string source_file_path; // .length() == 0 indicates unknown
std::string short_source_file_path;
size_t linenr; // 0 indicates unknown
void print() const {
if (!shared_obj) {
std::cerr << "\033[90m<unknown location>\033[0m" << std::endl;
return;
}
if (symbol.length() == 0) {
std::cerr << "\033[90msomewhere in\033[0m " << shared_obj << std::endl;
return;
}
if (source_file_path.length() == 0) {
std::cerr << "\033[90msomewhere in\033[0m " << symbol << std::endl;
return;
}
size_t fname_pos = split_path_filename(short_source_file_path);
std::cerr << "\033[90mat ";
if (fname_pos > 0)
std::cerr << short_source_file_path.substr(0, fname_pos + 1);
std::cerr << "\033[33m" << short_source_file_path.substr(fname_pos + 1)
<< "\033[90m:\033[31m" << linenr << " \033[90min\033[33m "
<< symbol << "\033[0m" << std::endl;
}
};
#ifdef BACKTRACE_DEBUG
struct Logger {
bool print_preamble = true;
template <typename T> Logger operator<<(T const &v) const {
if (print_preamble)
std::cerr << "[backtrace] ";
std::cerr << v;
return {false};
}
Logger operator<<(char const *v) const {
if (print_preamble)
std::cerr << "[backtrace] ";
if (v != nullptr)
std::cerr << v;
else
std::cerr << "<null>";
return {false};
}
Logger operator<<(std::ostream &(*f)(std::ostream &)) const {
if (print_preamble)
std::cerr << "[backtrace] ";
f(std::cerr);
return {false};
}
};
#else
struct Logger : std::ostream {
template <typename T> Logger const &operator<<(T const &v) const {
return *this;
}
Logger const &operator<<(std::ostream &(*f)(std::ostream &)) const {
return *this;
}
};
#endif
} // namespace _nice_backtrace_detail
void print_backtrace(size_t const skip_frames = 1) {
_nice_backtrace_detail::Logger const LOGGER;
static constexpr size_t const MAX_DEPTH = 64;
void *bt_buf[MAX_DEPTH];
int const stack_depth = backtrace(&bt_buf[0], MAX_DEPTH);
LOGGER << "obtained backtrace through " << stack_depth << " many frames"
<< std::endl;
Dl_info dlinfos[MAX_DEPTH];
struct link_map *lmaps[MAX_DEPTH];
std::multimap<std::string, size_t> dynamic_objects;
for (size_t i = skip_frames; i < stack_depth; ++i) {
LOGGER << "looking up dynamic link info for frame " << i
<< " with return addr. " << std::hex << bt_buf[i] << std::dec
<< std::endl;
if (dladdr1(bt_buf[i], &dlinfos[i], (void **)&lmaps[i], RTLD_DL_LINKMAP) ==
0)
std::cerr << "WARNING: failed to trace an address"
<< std::endl; // TODO: remove
else {
dynamic_objects.emplace(dlinfos[i].dli_fname, i);
LOGGER << "Got dynamic link info: " << '\n'
<< " Filename: " << dlinfos[i].dli_fname << '\n'
<< " Load address: " << dlinfos[i].dli_fbase << '\n'
<< " Nearest symbol: " << dlinfos[i].dli_sname << '\n'
<< " Nearest symb. address: " << std::hex << dlinfos[i].dli_saddr
<< std::dec << std::endl;
}
}
// call addr2line to get line numbers for each dynamic object
char *cwd = getcwd(nullptr, 0);
_nice_backtrace_detail::Frameinfo frameinfos[MAX_DEPTH] = {
{nullptr, "", "", "", 0}};
decltype(dynamic_objects.equal_range("")) range;
for (auto it = dynamic_objects.begin(); it != dynamic_objects.end();
it = range.second) {
range = dynamic_objects.equal_range(it->first);
// build the command string
static char const command_base[] = "addr2line --demangle -f -e";
size_t const command_len =
sizeof(command_base) + 1 + it->first.length() + (3 + 16) * stack_depth +
1; // reserve space for 64bit hex vals just to be safe
char *command = (char *)std::calloc(command_len, sizeof(char));
char *p = command +
std::sprintf(command, "%s %s", command_base, it->first.c_str());
LOGGER << "obtaining ELF offsets for " << it->first << std::endl;
for (auto dyobj = range.first; dyobj != range.second; ++dyobj) {
size_t const i = dyobj->second;
p += std::sprintf(p, " %p",
// convert virtual address to physical ELF offset. we
// take -1 because backtrace() gives the return address,
// i.e. the address of the next instruction after the
// call, but we actually want to print the trace of the
// call instruction.
(char *)bt_buf[i] - 1 - (size_t)(lmaps[i]->l_addr));
if (p - command > command_len) {
// this should be unreachable but just to be safe
std::cerr << "buffer overflow generating addr2line command, panicking"
<< std::endl;
std::exit(-1);
}
}
LOGGER << "constructed addr2line command:\n " << command << std::endl;
// invoke and read output
FILE *cfd = popen(command, "r"); // POSIX only
if (cfd == nullptr) {
std::cerr << "Could not generate backtrace (failed to launch addr2line)"
<< std::endl;
return;
}
for (auto dyobj = range.first; dyobj != range.second; ++dyobj) {
size_t const i = dyobj->second;
_nice_backtrace_detail::Frameinfo &finfo = frameinfos[i];
finfo.shared_obj = dlinfos[i].dli_fname;
// addr2line outputs in the form of
// <symbol>
// <source_file_path>:<line>
// for each address that we pass it, parse this format:
finfo.symbol = _nice_backtrace_detail::getline_from_fd(cfd);
std::string const &locspec = _nice_backtrace_detail::getline_from_fd(cfd);
size_t colon_idx = locspec.rfind(':');
finfo.source_file_path = std::string(locspec, 0, colon_idx);
if (finfo.source_file_path == "??")
finfo.source_file_path = "";
else
finfo.short_source_file_path =
_nice_backtrace_detail::shorten_path(finfo.source_file_path, cwd);
finfo.linenr =
std::strtoull(locspec.c_str() + colon_idx + 1, nullptr, 10);
LOGGER << "addr2line determined data for frame " << i << ":\n"
<< " Symbol: " << finfo.symbol << '\n'
<< " Source locspec: " << locspec << '\n'
<< " Parsed&shortened source file path: "
<< finfo.source_file_path << '\n'
<< " Parsed line number: " << finfo.linenr << std::endl;
}
std::free(command);
if (pclose(cfd) != 0)
std::exit(-1);
}
std::free(cwd);
size_t max_line_digits = 1;
for (size_t i = skip_frames; i < stack_depth; ++i) {
if (frameinfos[i].linenr != 0)
max_line_digits = std::max(
max_line_digits, (size_t)std::ceil(std::log10(frameinfos[i].linenr)));
}
LOGGER << "Determined max. linenr digits: " << max_line_digits
<< " -- now printing trace" << std::endl;
std::map<std::string, _nice_backtrace_detail::LineReader> linereaders;
for (size_t i = skip_frames; i < stack_depth; ++i) {
frameinfos[i].print();
if (frameinfos[i].source_file_path.length() == 0)
continue;
try {
auto it = linereaders.emplace(frameinfos[i].source_file_path,
frameinfos[i].source_file_path);
_nice_backtrace_detail::LineReader &reader = it.first->second;
if (frameinfos[i].linenr != 0)
print_context(reader, max_line_digits, frameinfos[i].linenr);
} catch (std::invalid_argument const &ex) {
std::cerr << "\033[31;1m " << std::setw(max_line_digits)
<< frameinfos[i].linenr << " │\033[0;90m " << ex.what()
<< "\033[0m" << std::endl;
}
}
}
void backtrace_assert(bool cond, char const *msg,
size_t const skip_frames = 2) {
if (!cond) {
std::cerr << "Assertion '\033[95m" << msg
<< "\033[0m' failed:" << std::endl;
print_backtrace(skip_frames);
std::exit(-1);
}
}
#endif
#ifndef NDEBUG
#include <cassert>
#undef assert
#define assert(cond) backtrace_assert((cond), #cond)
#endif