From 0193600e486759f4b0524b520e9128c2a3d19cbd Mon Sep 17 00:00:00 2001
From: Jean Guyomarc'h <jean@guyomarch.bzh>
Date: Sat, 28 May 2016 13:07:22 +0200
Subject: [PATCH] autotools: improve libunwind detection

Libuwind may not be shipped with a pkg-config file.
It can be distributed on the system, but the autotools
would fail to detect it because it relied only on pkg-config.

We now first check with pkg-config, and then try to compile and
link a program using libuwind to see if it is supported anyway.

This is a first step towards a working eina_log_backtrace on
Mac OS X.
---
 configure.ac        |  6 +----
 m4/efl_libunwind.m4 | 61 +++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 62 insertions(+), 5 deletions(-)
 create mode 100644 m4/efl_libunwind.m4

diff --git a/configure.ac b/configure.ac
index 40a2edffac..9fd46ba9a9 100644
--- a/configure.ac
+++ b/configure.ac
@@ -865,11 +865,7 @@ case "${build_profile}" in
      ;;
 esac
 
-PKG_CHECK_MODULES(UNWIND, [libunwind libunwind-generic],
-                  [have_unwind=yes], [have_unwind=no])
-AS_IF([test "x$have_unwind" = "xyes"],
-      [AC_DEFINE([HAVE_UNWIND], [1], [Have libunwind])])
-AM_CONDITIONAL(HAVE_UNWIND, test "x$have_unwind" = "xyes")
+EFL_CHECK_LIBUNWIND
 
 EINA_CONFIG([HAVE_ALLOCA_H], [test "x${ac_cv_working_alloca_h}" = "xyes"])
 EINA_CONFIG([SAFETY_CHECKS], [test "x${have_safety_checks}" = "xyes"])
diff --git a/m4/efl_libunwind.m4 b/m4/efl_libunwind.m4
new file mode 100644
index 0000000000..e9ca682cfb
--- /dev/null
+++ b/m4/efl_libunwind.m4
@@ -0,0 +1,61 @@
+dnl This code is public domain and can be freely used or copied.
+dnl File to auto-detect libunwind
+
+dnl Macro that checks for libunwind, first by using
+dnl pkg-config, then by trying to compile and link a simple
+dnl program, to see if libunwind is distributed on the system
+dnl but has no pkg-config support
+dnl
+dnl The biggest usecase is on Mac OS X, where there are no
+dnl pkg-config files, and the libunwind headers are lost
+dnl in an obscure place on the system (but whom the compilers
+dnl distributed by Apple are aware of).
+dnl
+dnl Usage: EFL_CHECK_LIBUNWIND
+dnl  will inconditionaly set UNWIND_CFLAGS and UNWIND_LIBS
+dnl  to follow pkg-config fashion.
+dnl
+AC_DEFUN([EFL_CHECK_LIBUNWIND],
+[dnl
+   dnl First, check with pkg-config
+   PKG_CHECK_MODULES([UNWIND], [libunwind libunwind-generic],
+                     [have_unwind=yes], [have_unwind=no])
+
+   dnl No pkg-config file... maybe system built-in?
+   if test "x${have_unwind}" = "xno"; then
+      AC_LANG_PUSH([C])
+      AC_LINK_IFELSE(
+	 [AC_LANG_PROGRAM(
+	    [[
+#include <libunwind.h>
+	    ]],
+	    [[
+	       unw_context_t ctx;
+	       unw_getcontext(&ctx);
+	    ]]
+	 )],
+	 [
+	    have_unwind="yes"
+	 ],
+	 [
+	    have_unwind="no"
+	 ]
+      )
+      AC_MSG_CHECKING([for native libunwind])
+      AC_MSG_RESULT([${have_unwind}])
+      AC_LANG_POP([C])
+
+      dnl Provide dummy variables to automake.
+      dnl In case pkg-config succeeded, these will be set and
+      dnl used in other automake files. To avoid, problems,
+      dnl we define empty variables.
+      UNWIND_CFLAGS=""
+      UNWIND_LIBS=""
+      AC_SUBST([UNWIND_CFLAGS])
+      AC_SUBST([UNWIND_LIBS])
+   fi
+
+   AS_IF([test "x$have_unwind" = "xyes"],
+	 [AC_DEFINE([HAVE_UNWIND], [1], [Have libunwind])])
+   AM_CONDITIONAL(HAVE_UNWIND, test "x$have_unwind" = "xyes")
+])