I spent some time last night getting the the development branch of GNU Radio to
compile on MacOS X 10.7. In the process, I saw some people having issues with
compiler/assembler AVX support, Apple's ancient GPLv2 "as", and Xcode's LLVM. I
succeeded in building and running GNU Radio using Xcode 4.3.2's tools (no
MacPorts gcc, llvm, or cctools). I'm posting what I learned, in hopes somebody
knows how to fix this from the GNU Radio source side (instead of patching
CMake, as I did).
The problem I saw, having to do with Clang compiler flag detection for ORC
during cmake:
-- Performing Test have_maltivec
-- Performing Test have_maltivec - Success
-- Performing Test have_mfpu_neon
-- Performing Test have_mfpu_neon - Success
-- Performing Test have_mfloat_abi_softfp
-- Performing Test have_mfloat_abi_softfp - Success
-- Performing Test have_funsafe_math_optimizations
-- Performing Test have_funsafe_math_optimizations - Success
...
-- Performing Test have_mpopcnt
-- Performing Test have_mpopcnt - Success
Note that I'm compiling on a Sandy Bridge Intel processor, so Altivec (PPC),
NEON (ARM), and float-ABI (ARM?) aren't available. Also, LLVM 3.0 doesn't
support -mpopcnt, and apparently doesn't support -munsafe_math_optimizations.
And yet, the detections are showing "Success". Sure enough, when I "make", volk
bombs out with:
cc1: error: unrecognized command line option "-mfpu=neon"
cc1: error: unrecognized command line option "-mfloat-abi=softfp"
Examining build/volk/CMakeFiles/CMakeOutput.log, the command line executed for
detecting the Altivec flag is:
/usr/bin/c++ -Dhave_maltivec -maltivec -o
CMakeFiles/cmTryCompileExec.dir/src.cxx.o -c
/Users/jboone/tmp/gnuradio/build/volk/CMakeFiles/CMakeTmp/src.cxx
Creating my own src.cxx ("int main() { return 0; }") and trying this out yields:
clang: warning: argument unused during compilation: '-maltivec'
Clang warns about the unrecognized flag, but CMake doesn't consider it an
error. Why? Examining volk/lib/CMakeLists.txt, I see that CMake's
CheckCXXCompilerFlag is included, and CHECK_CXX_COMPILER_FLAG is called with
each flag to test.
Looking at CMake's CHECK_CXX_COMPILER_FLAG, I see it tests the compiler's
stdout (or stderr?) against these regular expressions:
# Some compilers do not fail with a bad flag
FAIL_REGEX "unrecognized .*option" # GNU
FAIL_REGEX "unknown .*option" # Clang
FAIL_REGEX "ignoring unknown option" # MSVC
FAIL_REGEX "warning D9002" # MSVC, any lang
FAIL_REGEX "[Uu]nknown option" # HP
FAIL_REGEX "[Ww]arning: [Oo]ption" # SunPro
FAIL_REGEX "command option .* is not recognized" # XL
FAIL_REGEX "not supported in this configuration; ignored" # AIX
FAIL_REGEX "File with unknown suffix passed to linker" # PGI
None of these regex tests will catch the Clang warning above.
My first inclination was to see if I could set a Clang flag (like "-Werror") to
cause unused arguments to produce an error. But I can't tell how to do that
with CMake. If somebody knows how to do this from within the GNU Radio sources,
that would be ideal. Instead, I patched CMake as follows:
--- /opt/local/share/cmake-2.8/Modules/CheckCXXCompilerFlag.cmake.orig
2012-05-04 23:41:16.000000000 -0700
+++ /opt/local/share/cmake-2.8/Modules/CheckCXXCompilerFlag.cmake
2012-05-04 23:43:19.000000000 -0700
@@ -29,6 +29,7 @@
# Some compilers do not fail with a bad flag
FAIL_REGEX "unrecognized .*option" # GNU
FAIL_REGEX "unknown .*option" # Clang
+ FAIL_REGEX "argument unused during compilation" # Clang
FAIL_REGEX "ignoring unknown option" # MSVC
FAIL_REGEX "warning D9002" # MSVC, any lang
FAIL_REGEX "[Uu]nknown option" # HP
This results in more sensible flag detection for ORC during cmake:
-- Performing Test have_maltivec
-- Performing Test have_maltivec - Failed
-- Performing Test have_mfpu_neon
-- Performing Test have_mfpu_neon - Failed
-- Performing Test have_mfloat_abi_softfp
-- Performing Test have_mfloat_abi_softfp - Failed
-- Performing Test have_funsafe_math_optimizations
-- Performing Test have_funsafe_math_optimizations - Failed
...
-- Performing Test have_mpopcnt
-- Performing Test have_mpopcnt - Failed
...
-- GCC missing xgetbv, Overruled arch avx
-- Check size of void*[8]
-- Check size of void*[8] - done
-- CPU width is 64 bits, Overruled arch 32
-- Available architectures:
generic;64;3dnow;abm;mmx;sse;sse2;orc;norc;sse3;ssse3;sse4_a;sse4_1;sse4_2
-- Available machines:
generic_orc;sse2_64_orc;sse3_64_orc;ssse3_64_orc;sse4_1_64_orc
...and more importantly, I can compile GNU Radio and run gnuradio-companion.
I see some similar patch history for CMake that suggests my fix is a good one:
http://public.kitware.com/Bug/view.php?id=12394
I looked at the CMake repository, and it looks like they haven't yet identified
or fixed this problem:
http://cmake.org/gitweb?p=cmake.git;a=blob;f=Modules/CheckCXXCompilerFlag.cmake;hb=HEAD
So I'll submit a patch to CMake. Of course, until a new CMake is released,
MacOS builders will run into this problem. So if anybody familiar with CMake
knows a way to fix this from GNU Radio, that would be splendid!
- Jared
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