Problem: no backtrace is printed on assert

Solution: add an optional dependency on libunwind, and if present
use it to print the backtrace when zmq_abort is called.

Makefile.am

@@ -277,10 +277,11 @@ endif
 endif
 endif
 
-src_libzmq_la_CPPFLAGS = $(CODE_COVERAGE_CPPFLAGS)
-src_libzmq_la_CFLAGS = $(CODE_COVERAGE_CFLAGS)
-src_libzmq_la_CXXFLAGS = @LIBZMQ_EXTRA_CXXFLAGS@ $(CODE_COVERAGE_CXXFLAGS)
-src_libzmq_la_LIBADD = $(CODE_COVERAGE_LDFLAGS)
+src_libzmq_la_CPPFLAGS = $(CODE_COVERAGE_CPPFLAGS) $(LIBUNWIND_CFLAGS)
+src_libzmq_la_CFLAGS = $(CODE_COVERAGE_CFLAGS) $(LIBUNWIND_CFLAGS)
+src_libzmq_la_CXXFLAGS = @LIBZMQ_EXTRA_CXXFLAGS@ $(CODE_COVERAGE_CXXFLAGS) \
+	$(LIBUNWIND_CFLAGS)
+src_libzmq_la_LIBADD = $(CODE_COVERAGE_LDFLAGS) $(LIBUNWIND_LIBS)
 
 if USE_LIBSODIUM
 src_libzmq_la_CPPFLAGS += ${sodium_CFLAGS}

configure.ac

@@ -632,6 +632,16 @@ else
     AC_SUBST(pkg_config_defines, "")
 fi
 
+PKG_CHECK_MODULES(LIBUNWIND, [libunwind],
+    [
+        AC_DEFINE(HAVE_LIBUNWIND, 1, [The libunwind library is to be used])
+        AC_SUBST([LIBUNWIND_CFLAGS])
+        AC_SUBST([LIBUNWIND_LIBS])
+    ],
+    [
+        AC_MSG_WARN([Cannot find libunwind])
+    ])
+
 # Subst LIBZMQ_EXTRA_CFLAGS & CXXFLAGS & LDFLAGS
 AC_SUBST(LIBZMQ_EXTRA_CFLAGS)
 AC_SUBST(LIBZMQ_EXTRA_CXXFLAGS)

src/err.cpp

@@ -81,6 +81,7 @@ void zmq::zmq_abort(const char *errmsg_)
     RaiseException (0x40000015, EXCEPTION_NONCONTINUABLE, 1, extra_info);
 #else
     (void)errmsg_;
+    print_backtrace();
     abort ();
 #endif
 }
@@ -384,3 +385,61 @@ int zmq::wsa_error_to_errno (int errcode)
 }
 
 #endif
+
+#ifdef HAVE_LIBUNWIND
+
+#define UNW_LOCAL_ONLY
+#include <libunwind.h>
+#include <dlfcn.h>
+#include <cxxabi.h>
+
+void zmq::print_backtrace (void)
+{
+    Dl_info dl_info;
+    unw_cursor_t cursor;
+    unw_context_t ctx;
+    unsigned frame_n = 0;
+
+    unw_getcontext (&ctx);
+    unw_init_local (&cursor, &ctx);
+
+    while (unw_step (&cursor) > 0) {
+        unw_word_t offset;
+        unw_proc_info_t p_info;
+        const char *file_name;
+        char *demangled_name;
+        char func_name[256] = "";
+        void *addr;
+        int rc;
+
+        if (unw_get_proc_info (&cursor, &p_info))
+            break;
+
+        addr = (void *)(p_info.start_ip + offset);
+
+        if (dladdr (addr, &dl_info) && dl_info.dli_fname)
+            file_name = dl_info.dli_fname;
+        else
+            file_name = "?";
+
+        rc = unw_get_proc_name (&cursor, func_name, 256, &offset);
+        if (rc == -UNW_ENOINFO)
+            strcpy(func_name, "?");
+
+        demangled_name = abi::__cxa_demangle (func_name, NULL, NULL, &rc);
+
+        printf ("#%u  %p in %s (%s+0x%lx)\n", frame_n++, addr, file_name,
+                rc ? func_name : demangled_name, (unsigned long) offset);
+        free (demangled_name);
+    }
+
+    fflush (stdout);
+}
+
+#else
+
+void zmq::print_backtrace (void)
+{
+}
+
+#endif

src/err.hpp

@@ -62,6 +62,7 @@ namespace zmq
 {
     const char *errno_to_string (int errno_);
     void zmq_abort (const char *errmsg_);
+    void print_backtrace (void);
 }
 
 #ifdef ZMQ_HAVE_WINDOWS