build: only enable backtrace(3) in maintainer mode

Using backtrace() is of no use when building with PIE (which most
distro compilers do by default) and prevents catching the coredump
for later retracing, which is needed since distros usually don't
install debug symbols by default either.

This patch thus only enables backtrace() when --enable-maintainer-mode
is passed and also tries to explicitly disable PIE.

configure.ac

@@ -80,8 +80,16 @@ AC_DEFINE_UNQUOTED(WIRED_STORAGEDIR, "${wired_storagedir}",
 
 AC_CHECK_HEADERS(linux/types.h linux/if_alg.h)
 
-AC_CHECK_HEADERS_ONCE(execinfo.h)
-AC_CHECK_LIB(execinfo, backtrace)
+# In maintainer mode: try to build with application backtrace and disable PIE.
+if (test "${USE_MAINTAINER_MODE}" = yes); then
+	AC_SEARCH_LIBS([backtrace], [execinfo],
+		[
+			AC_DEFINE([HAVE_BACKTRACE], [1],
+				[Define to 1 if you have backtrace(3).])
+			CFLAGS="$CFLAGS -fno-PIE"
+			LDFLAGS="$LDFLAGS -no-pie"
+		])
+fi
 
 AC_ARG_ENABLE([daemon], AC_HELP_STRING([--disable-daemon],
 				[don't install iwd system daemon]),

src/backtrace.c

@@ -27,7 +27,7 @@
 #define _GNU_SOURCE
 #include <features.h>
 
-#ifdef HAVE_EXECINFO_H
+#ifdef HAVE_BACKTRACE
 #include <stdlib.h>
 #include <string.h>
 #include <sys/types.h>

src/backtrace.h

@@ -19,7 +19,7 @@
  *  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
  *
  */
-#ifdef HAVE_EXECINFO_H
+#ifdef HAVE_BACKTRACE
 void __iwd_backtrace_init();
 void __iwd_backtrace_print(unsigned int offset);
 #endif

src/main.c

@@ -445,7 +445,7 @@ int main(int argc, char *argv[])
 	if (debugopt)
 		l_debug_enable(debugopt);
 
-#ifdef HAVE_EXECINFO_H
+#ifdef HAVE_BACKTRACE
 	__iwd_backtrace_init();
 #endif