From 233413841882608c6d5b98b6ce89fcb8a292db82 Mon Sep 17 00:00:00 2001
From: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Date: Sat, 6 Aug 2016 10:22:34 +0200
Subject: [PATCH] configure.ac: fix architecture detection

The current architecture detection, based on the "host_cpu" part of the
tuple does not work properly for a number of reason:

 - The code assumes that if host_cpu starts with "arm" then ARM
   instructions are available, which is incorrect. Indeed, Cortex-M
   platforms can run Linux, they are ARM platforms (so host_cpu = arm),
   but they don't support ARM instructions: they support only the
   Thumb-2 instruction set.

 - The armv7 case is also not very useful, as it is not standard at all
   to pass armv7 as host_cpu even if the host system is actually ARMv7
   based.

 - For the same reason, the armv8 case is not very useful: armv8 is
   never used as the host_cpu part of a tuple.

So, this commit moves away from a host_cpu based logic, and instead
tests using AC_CHECK_DECLS() the built-in definitions of the compiler:

 - If we have __ARM_ARCH_ISA_ARM defined, then it's an ARM processor
   that supports the ARM instruction set (this allows to exclude Thumb-2
   only processors).

 - If we have __ARM_ARCH_7A__, then we have an ARMv7-A processor, and
   we can enable the corresponding optimizations

 - Same for __i386__ and __x86_64__.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
---
Submitted upstream, under a slightly different form so that it applies
on master:

  https://lists.freedesktop.org/archives/pulseaudio-discuss/2016-August/026600.html
---
 configure.ac | 27 +++++++++------------------
 1 file changed, 9 insertions(+), 18 deletions(-)

diff --git a/configure.ac b/configure.ac
index 6f9553b..836c6ad 100644
--- a/configure.ac
+++ b/configure.ac
@@ -55,24 +55,15 @@ AS_CASE(["${host}"],
 )
 AC_SUBST(PLATFORM_CFLAGS)
 
-AS_CASE(["${host_cpu}"],
-    [i?86|x86_64],
-        [
-         HAVE_X86=1
-        ],
-    [armv7*|armv8*],
-        [
-         HAVE_ARM=1
-         HAVE_ARMV7=1
-         ARCH_CFLAGS="-DWEBRTC_ARCH_ARM -DWEBRTC_ARCH_ARM_V7"
-        ],
-    [arm*],
-        [
-         HAVE_ARM=1
-         ARCH_CFLAGS="-DWEBRTC_ARCH_ARM"
-        ]
-    # FIXME: Add MIPS support, see webrtc/BUILD.gn for defines
-)
+# Testing __ARM_ARCH_ISA_ARM since the code contains ARM instructions,
+# which don't work on Thumb-2 only platforms (ARMv7-M).
+AC_CHECK_DECLS([__ARM_ARCH_ISA_ARM],
+	[HAVE_ARM=1; ARCH_CFLAGS="${ARCH_CFLAGS} -DWEBRTC_ARCH_ARM"])
+AC_CHECK_DECLS([__ARM_ARCH_7A__],
+	[HAVE_ARMV7=1; ARCH_CFLAGS="${ARCH_CFLAGS} -DWEBRTC_ARCH_ARM_V7"])
+AC_CHECK_DECLS([__i386__], [HAVE_X86=1])
+AC_CHECK_DECLS([__x86_64__], [HAVE_X86=1])
+
 AM_CONDITIONAL(HAVE_X86, [test "x${HAVE_X86}" = "x1"])
 AM_CONDITIONAL(HAVE_ARM, [test "x${HAVE_ARM}" = "x1"])
 AM_CONDITIONAL(HAVE_ARMV7, [test "x${HAVE_ARMV7}" = "x1"])
-- 
2.7.4