Offer a configure --with-unwind switch

Conflicts:
	.travis.yml
	bin/varnishd/cache/cache_panic.c

.travis.yml

@@ -40,7 +40,7 @@ before_install:
     if [[ "$TRAVIS_OS_NAME" == "osx" ]]; then
       export PATH="/usr/local/opt/sphinx-doc/bin:$PATH"
     elif [[ -n "$SAN_FLAGS" ]]; then
-      export CONFIGURE_ARGS="--enable-developer-warnings --enable-debugging-symbols --disable-stack-protector --with-persistent-storage ${SAN_FLAGS}"
+      export CONFIGURE_ARGS="--enable-developer-warnings --enable-debugging-symbols --disable-stack-protector --with-persistent-storage --with-unwind ${SAN_FLAGS}"
       export ASAN_OPTIONS=abort_on_error=1,detect_odr_violation=1,detect_leaks=1,detect_stack_use_after_return=1,detect_invalid_pointer_pairs=1,handle_segv=0,handle_sigbus=0,use_sigaltstack=0,disable_coredump=0
       export LSAN_OPTIONS=abort_on_error=1,use_sigaltstack=0,suppressions=$(pwd)/tools/lsan.suppr
       export TSAN_OPTIONS=abort_on_error=1,halt_on_error=1,use_sigaltstack=0,suppressions=$(pwd)/tools/tsan.suppr

bin/varnishd/Makefile.am

@@ -173,6 +173,11 @@ varnishd_LDADD = \
 	@PCRE_LIBS@ \
 	${DL_LIBS} ${PTHREAD_LIBS} ${NET_LIBS} ${RT_LIBS} ${LIBM}
 
+if WITH_UNWIND
+varnishd_CFLAGS += -DUNW_LOCAL_ONLY
+varnishd_LDADD += ${LIBUNWIND_LIBS}
+endif
+
 noinst_PROGRAMS = vhp_gen_hufdec
 vhp_gen_hufdec_SOURCES = hpack/vhp_gen_hufdec.c
 vhp_gen_hufdec_CFLAGS = @SAN_CFLAGS@ \

bin/varnishd/cache/cache_panic.c

@@ -29,7 +29,11 @@
 
 #include "config.h"
 
+#ifdef WITH_UNWIND
+#include <libunwind.h>
+#else
 #include <execinfo.h>
+#endif
 #include <errno.h>
 #include <stdio.h>
 #include <stdlib.h>
@@ -575,6 +579,47 @@ pan_sess(struct vsb *vsb, const struct sess *sp)
 
 /*--------------------------------------------------------------------*/
 
+#ifdef WITH_UNWIND
+
+static void
+pan_backtrace(struct vsb *vsb)
+{
+	unw_cursor_t cursor; unw_context_t uc;
+	unw_word_t ip, sp;
+	unw_word_t offp;
+	char fname[1024];
+	int ret;
+
+	VSB_printf(vsb, "Backtrace:\n");
+	VSB_indent(vsb, 2);
+
+	ret = unw_getcontext(&uc);
+	if (ret != 0) {
+		VSB_printf(vsb, "Backtrace not available "
+		    "(unw_getcontext returned %d)\n", ret);
+		return;
+	}
+	unw_init_local(&cursor, &uc);
+	if (ret != 0) {
+		VSB_printf(vsb, "Backtrace not available "
+		    "(unw_init_local returned %d)\n", ret);
+		return;
+	}
+	while (unw_step(&cursor) > 0) {
+		fname[0] = '\0';
+		ip = sp = 0;
+		unw_get_reg(&cursor, UNW_REG_IP, &ip);
+		unw_get_reg(&cursor, UNW_REG_SP, &sp);
+		unw_get_proc_name(&cursor, fname, sizeof(fname), &offp);
+		VSB_printf(vsb, "ip=0x%lx, sp=0x%lx <%s+0x%lx>\n", (long) ip,
+		    (long) sp, fname[0] ? fname : "???", offp);
+	}
+
+	VSB_indent(vsb, -2);
+}
+
+#else /* WITH_UNWIND */
+
 #define BACKTRACE_LEVELS	10
 
 static void
@@ -616,6 +661,8 @@ pan_backtrace(struct vsb *vsb)
 	VSB_indent(vsb, -2);
 }
 
+#endif /* WITH_UNWIND */
+
 /*--------------------------------------------------------------------*/
 
 static void __attribute__((__noreturn__))

configure.ac

@@ -336,9 +336,25 @@ esac
 AC_SUBST(JEMALLOC_LDADD)
 
 AC_CHECK_FUNCS([setproctitle])
-AC_SEARCH_LIBS(backtrace, [execinfo], [], [
-   AC_MSG_ERROR([Could not find backtrace() support])
-])
+
+# if the default libexecinfo on alpine causes issues, you can use libunwind
+AC_ARG_WITH([unwind],
+            [AS_HELP_STRING([--with-unwind],
+              [use libunwind to print stacktraces (use libexecinfo otherwise). Recommended on alpine linux. Defaults to no.])])
+
+if test "$with_unwind" = yes; then
+    PKG_CHECK_MODULES([LIBUNWIND], [libunwind])
+    AC_DEFINE([WITH_UNWIND], [1],
+              [Define to 1 to use libunwind instead of libexecinfo])
+else
+    AC_SEARCH_LIBS(backtrace, [execinfo], [], [
+        AC_MSG_ERROR([Could not find backtrace() support])
+    ])
+fi
+
+AM_CONDITIONAL([WITH_UNWIND],
+	[test "$with_unwind" = yes])
+
 # white lie - we don't actually test it
 AC_MSG_CHECKING([whether daemon() works])
 case $target in