From: Marco Costalba <mcostalba@gmail.com>
Date: Sun, 1 Sep 2013 16:16:55 +0000 (-0700)
Subject: Improve ARM compatibility
X-Git-Url: https://git.sesse.net/?p=stockfish;a=commitdiff_plain;h=aee404f53269c79ec42eb4d54b0bc6e2d8b1c340;hp=0915f85895733ff8ed8e480fa9c83c25c296ea1d

Improve ARM compatibility

STANDALONE-TOOLCHAIN.html in Android NDK says:

It is recommended to use the -mthumb compiler flag to force the generation
of 16-bit Thumb-1 instructions (the default being 32-bit ARM ones).

If you want to target the 'armeabi-v7a' ABI, you will need ensure that the
following two flags are being used:

  CFLAGS='-march=armv7-a -mfloat-abi=softfp'

Note: The first flag enables Thumb-2 instructions, and the second one
      enables H/W FPU instructions while ensuring that floating-point
      parameters are passed in core registers, which is critical for
      ABI compatibility. Do *not* use these flags separately!

Thanks to Peter Osterlund for pointout this doc and for showing me
an example Makefile to follow.

No functional change.
---

diff --git a/src/Makefile b/src/Makefile
index f8d65ccb..67cd382a 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -296,7 +296,7 @@ ifeq ($(optimize),yes)
 		endif
 
 		ifeq ($(arch),armv7)
-			CXXFLAGS += -fno-gcse
+			CXXFLAGS += -fno-gcse -mthumb -march=armv7-a -mfloat-abi=softfp
 		endif
 	endif