--- /dev/null
+From 9bef473d17ec01efe760462271791dfaaea280c0 Mon Sep 17 00:00:00 2001
+From: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
+Date: Wed, 29 Jul 2015 22:35:19 +0200
+Subject: [PATCH 1/3] configure: refactor backtrace() detection
+
+The current code assumes that if __GLIBC__ is not defined, backtrace
+support is not available, and defines BTRFS_DISABLE_BACKTRACE.
+
+However, this macro is already defined by the configure.ac script when
+--disable-backtrace is passed. This means that if you are using a C
+library like musl which does not define __GLIBC__, and you pass
+--disable-backtrace, you get a macro redefinition.
+
+Instead of relying on __GLIBC__, this commit implements a proper
+configure.ac based detection of backtrace support:
+
+ * If the user passes --enable-backtrace, we check if the backtrace()
+ function is available. If not, we abort the configure process with
+ an error. Otherwise we enable backtrace support by defining
+ HAVE_BACKTRACE.
+
+ * If the user passes --disable-backtrace, then we don't enable
+ backtrace support.
+
+ * If the user passes nothing special, we auto-detect: if backtrace()
+ is available, we use it, otherwise we simply warn at configure time
+ but not fail.
+
+Upstream-status: pending
+Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
+Signed-off-by: Brendan Heading <brendanheading@gmail.com>
+---
+ configure.ac | 32 ++++++++++++++++++++++----------
+ kerncompat.h | 9 ++++-----
+ 2 files changed, 26 insertions(+), 15 deletions(-)
+
+diff --git a/configure.ac b/configure.ac
+index c3a22d1..e936a10 100644
+--- a/configure.ac
++++ b/configure.ac
+@@ -63,22 +63,34 @@ AC_DEFUN([PKG_STATIC], [
+ fi
+ ])
+
+-
++# Provide a --{enable,disable}-backtrace option. If not passed, set
++# enable_backtrace to 'auto' so that we try to enable backtrace
++# support if available, but if not available, we gracefully fallback
++# without backtrace support.
+ AC_ARG_ENABLE([backtrace],
+ AS_HELP_STRING([--disable-backtrace], [disable btrfs backtrace]),
+- [], [enable_backtrace=yes]
++ [enable_backtrace=${enableval}], [enable_backtrace=auto]
+ )
+
+-AS_IF([test "x$enable_backtrace" = xno], [
+- AC_DEFINE([BTRFS_DISABLE_BACKTRACE], [1], [disable backtrace stuff in kerncompat.h ])
+-])
+-
+-if test "x$enable_backtrace" = xyes; then
+- AC_CHECK_HEADERS([execinfo.h])
+- AC_CHECK_FUNCS([backtrace backtrace_symbols_fd], [],
+- AC_MSG_ERROR([standard library does not have backtrace support]))
++# Backtrace support requested (enable_backtrace is either 'yes' or
++# 'auto'), so check for needed headers and functions.
++if test "x$enable_backtrace" != xno; then
++ AC_CHECK_HEADERS([execinfo.h])
++ AC_CHECK_FUNCS([backtrace backtrace_symbols_fd])
+ fi
+
++if test "x$ac_cv_func_backtrace" = xno; then
++ # If backtrace support was requested but not available, we fail if
++ # --enable-backtrace was passed, or we simply warn if we're
++ # auto-detecting.
++ if test "x$enable_backtrace" = xyes ; then
++ AC_MSG_ERROR([standard library does not have backtrace support])
++ elif test "x$enable_backtrace" = xauto ; then
++ AC_MSG_WARN([standard library does not have backtrace support, disabled])
++ fi
++else
++ AC_DEFINE([HAVE_BACKTRACE], [1], [Enable backtrace support])
++fi
+
+ AC_ARG_ENABLE([documentation],
+ AS_HELP_STRING([--disable-documentation], [do not build domumentation]),
+diff --git a/kerncompat.h b/kerncompat.h
+index 5d92856..8318665 100644
+--- a/kerncompat.h
++++ b/kerncompat.h
+@@ -33,11 +33,10 @@
+ #include <features.h>
+
+ #ifndef __GLIBC__
+-#define BTRFS_DISABLE_BACKTRACE
+ #define __always_inline __inline __attribute__ ((__always_inline__))
+ #endif
+
+-#ifndef BTRFS_DISABLE_BACKTRACE
++#ifdef HAVE_BACKTRACE
+ #include <execinfo.h>
+ #endif
+
+@@ -65,7 +64,7 @@
+ #define ULONG_MAX (~0UL)
+ #endif
+
+-#ifndef BTRFS_DISABLE_BACKTRACE
++#ifdef HAVE_BACKTRACE
+ #define MAX_BACKTRACE 16
+ static inline void print_trace(void)
+ {
+@@ -285,7 +284,7 @@ static inline long IS_ERR(const void *ptr)
+ #define vmalloc(x) malloc(x)
+ #define vfree(x) free(x)
+
+-#ifndef BTRFS_DISABLE_BACKTRACE
++#ifdef HAVE_BACKTRACE
+ #define BUG_ON(c) assert_trace(#c, __FILE__, __func__, __LINE__, !(c))
+ #else
+ #define BUG_ON(c) assert(!(c))
+@@ -293,7 +292,7 @@ static inline long IS_ERR(const void *ptr)
+
+ #define WARN_ON(c) BUG_ON(c)
+
+-#ifndef BTRFS_DISABLE_BACKTRACE
++#ifdef HAVE_BACKTRACE
+ #define ASSERT(c) assert_trace(#c, __FILE__, __func__, __LINE__, (c))
+ #else
+ #define ASSERT(c) assert(c)
+--
+2.4.3
+
--- /dev/null
+From 1d99ae25bb1bd4879c6f20f607faf3040018ee84 Mon Sep 17 00:00:00 2001
+From: Brendan Heading <brendanheading@gmail.com>
+Date: Thu, 30 Jul 2015 15:44:52 +0100
+Subject: [PATCH 2/3] configure: refactor always_inline detection
+
+Use configure.ac to detect the availability of the always_inline glibc
+macro, and define it only if it does not exist.
+
+Signed-off-by: Brendan Heading <brendanheading@gmail.com>
+---
+ configure.ac | 1 +
+ kerncompat.h | 2 +-
+ 2 files changed, 2 insertions(+), 1 deletion(-)
+
+diff --git a/configure.ac b/configure.ac
+index e936a10..d3d81a1 100644
+--- a/configure.ac
++++ b/configure.ac
+@@ -41,6 +41,7 @@ AC_PATH_PROG([RMDIR], [rmdir], [rmdir])
+
+ AC_CHECK_FUNCS([openat], [],
+ [AC_MSG_ERROR([cannot find openat() function])])
++AC_CHECK_DECLS([__always_inline])
+
+ m4_ifndef([PKG_PROG_PKG_CONFIG],
+ [m4_fatal([Could not locate the pkg-config autoconf
+diff --git a/kerncompat.h b/kerncompat.h
+index 8318665..757b9b4 100644
+--- a/kerncompat.h
++++ b/kerncompat.h
+@@ -32,7 +32,7 @@
+
+ #include <features.h>
+
+-#ifndef __GLIBC__
++#ifndef HAVE_DECL___ALWAYS_INLINE
+ #define __always_inline __inline __attribute__ ((__always_inline__))
+ #endif
+
+--
+2.4.3
+