Use libunwind for stack unwinding

The backtrace() interface is not available on Alpine. ([#245])

.github/workflows/release.yml

@@ -21,6 +21,8 @@ jobs:
             automake \
             curl \
             libcurl4-openssl-dev \
+            libunwind \
+            libunwind-dev \
             git \
             libev-dev \
             libtool \

Makefile.am

@@ -571,8 +571,8 @@ EXTRA_DIST = \
     generate_commit_hash.sh \
     commit_hash.h
 
-AM_CXXFLAGS = -Wall -Werror $(PTHREAD_CFLAGS) $(libev_CFLAGS) $(SQLITE3_CFLAGS) $(CURL_CFLAGS) $(CLBOSS_CXXFLAGS)
-LDADD = libclboss.la $(PTHREAD_LIBS) $(libev_LIBS) $(SQLITE3_LIBS) $(CURL_LIBS)
+AM_CXXFLAGS = -Wall -Werror $(PTHREAD_CFLAGS) $(libev_CFLAGS) $(SQLITE3_CFLAGS) $(CURL_CFLAGS) $(CLBOSS_CXXFLAGS) $(LIBUNWIND_CFLAGS)
+LDADD = libclboss.la $(PTHREAD_LIBS) $(libev_LIBS) $(SQLITE3_LIBS) $(CURL_LIBS) $(LIBUNWIND_LIBS)
 
 ACLOCAL_AMFLAGS = -I m4
 

README.md

@@ -44,20 +44,23 @@ Debian-derived systems:
 * `libev-dev`
 * `libcurl4-gnutls-dev`
 * `libsqlite3-dev`
+* `libunwind-dev`
 
 RPM-dervied :
 * `groupinstall "Development Tools"`
 * `pkg-config`
 * `libev-devel`
 * `libcurl-devel`
 * `libsqlite3x-devel`
+* `libunwind-devel`
 
 Alpine:
 * `build-base`
 * `pkgconf`
 * `libev-dev`
 * `curl-dev`
 * `sqlite-dev`
+* `libunwind-dev`
 
 Equivalent packages have a good probability of existing in
 non-Debian-derived distributions as well.
@@ -132,6 +135,7 @@ release:
     pkg install libev
     pkg install pkgconf
     pkg install sqlite3
+    pkg install libunwind
 
 In addition, you have to use `gmake` for building, not the
 system `make`, as the included `libsecp256k1` requires

Util/BacktraceException.hpp

@@ -9,13 +9,17 @@
 #include <stdlib.h>
 #include <string.h>
 #include <string>
+#include <vector>
 
 #ifdef HAVE_CONFIG_H
 # include"config.h"
 #endif
 
 extern std::string g_argv0;
 
+#define UNW_LOCAL_ONLY
+#include <libunwind.h>
+
 namespace Util {
 
 /** class Util::BacktraceException<E>
@@ -54,23 +58,40 @@ class BacktraceException : public T {
 	static constexpr size_t MAX_FRAMES = 100;
 	mutable bool formatted_ = false;
 	mutable std::string full_message_;
-	mutable void* backtrace_addresses_[MAX_FRAMES];
+	mutable std::vector<unw_word_t> backtrace_addresses_;
 	mutable size_t stack_depth;
 
 	void capture_backtrace() {
-		memset(backtrace_addresses_, 0, sizeof(backtrace_addresses_));
-		stack_depth = backtrace(backtrace_addresses_, sizeof(backtrace_addresses_) / sizeof(void*));
+		unw_cursor_t cursor;
+		unw_context_t context;
+		unw_getcontext(&context);
+		unw_init_local(&cursor, &context);
+
+		while (unw_step(&cursor) > 0 && backtrace_addresses_.size() < MAX_FRAMES) {
+			unw_word_t ip;
+			unw_get_reg(&cursor, UNW_REG_IP, &ip);
+			backtrace_addresses_.push_back(ip);
+		}
+
+		stack_depth = backtrace_addresses_.size();
 	}
 
 	std::string format_backtrace() const {
-		char** symbols = backtrace_symbols(backtrace_addresses_, stack_depth);
+		// Create an array of pointers compatible with `backtrace_symbols`.
+		std::vector<void*> pointers(backtrace_addresses_.size());
+		for (size_t i = 0; i < backtrace_addresses_.size(); ++i) {
+			pointers[i] = reinterpret_cast<void*>(backtrace_addresses_[i]);
+		}
+
+		// Use `backtrace_symbols` with the adapted pointers.
+		char** symbols = backtrace_symbols(pointers.data(), stack_depth);
 		std::ostringstream oss;
 		for (size_t i = 0; i < stack_depth; ++i) {
 			oss << '#' << std::left << std::setfill(' ') << std::setw(2) << i << ' ';
-			auto line = addr2line(backtrace_addresses_[i]);
+			auto line = addr2line(pointers[i]);
 			if (line.find("??") != std::string::npos) {
 				// If addr2line doesn't find a good
-				// answer use basic information
+				// answer, use basic information
 				// instead.
 				oss << symbols[i] << std::endl;
 			} else {

configure.ac

@@ -50,6 +50,22 @@ AX_LIB_CURL(,[:],[
 	AC_MSG_ERROR([Need libcurl.])
 ])
 
+# Check for libunwind
+PKG_CHECK_MODULES([LIBUNWIND], [libunwind], [
+  AC_DEFINE([HAVE_LIBUNWIND], [1], [Define if libunwind is available])
+], [
+  AC_MSG_ERROR([libunwind is required but not found])
+])
+
+# https://github.com/ZmnSCPxj/clboss/issues/245
+case "$host_os" in
+  *alpine*)
+    LDFLAGS="$LDFLAGS -lexecinfo"
+    ;;
+esac
+
+AC_SUBST(LDFLAGS)
+
 # Checks for header files.
 
 # Checks for typedefs, structures, and compiler characteristics.

flake.nix

@@ -23,6 +23,7 @@
             libev
             libevdev
             curl
+            libunwind
             sqlite
             bind
             autoconf