Update 01/12/2010: thanks to a reader’s comment it appears that you also need to have a version Xcode greater than 3.0 installed on your Mac in order to properly compile the CUDA 2.3 SDK.

You may be greeted by a similar compilation error when building NVIDIA’s CUDA SDK 2.3 on Mac OS X Snow Leopard:

make -C src/3DFD/
ld: warning: in obj/i386/release/3dfd.cu.o, file is not of required architecture
ld: warning: in /usr/local/cuda/lib/libcudart.dylib, file is not of required architecture

Undefined symbols:
“_main”, referenced from:
start in crt1.10.6.o
ld: symbol(s) not found
collect2: ld returned 1 exit status
make[1]: *** [../../bin/darwin/release/3dfd] Error 1
make: *** [src/3DFD/Makefile.ph_build] Error 2

The first error message stems from a mismatch between 32 and 64 bits objects/libraries, my Macbook which was running Snow Leopard out of the box was apparently running in 32 bits mode:

$uname -a
Darwin XXXX-MacBook.local 10.2.0 Darwin Kernel Version 10.2.0: Tue Nov  3 10:37:10 PST 2009; root:xnu-1486.2.11~1/RELEASE_I386 i386

If we look into the shared Makefile of the CUDA SDK (by default in /Developer/GPU Computing/C/common/common.mk) we find the following code responsible for selecting the adequate 32 or 64 bits compilation flags depending on which OS is detected:

# Determining the necessary Cross-Compilation Flags
# 32-bit OS, but we target 64-bit cross compilation
ifeq ($(x86_64),1)
NVCCFLAGS += -m64
LIB_ARCH = x86_64
ifneq ($(DARWIN),)
CXX_ARCH_FLAGS += -arch x86_64
else
CXX_ARCH_FLAGS += -m64
endif
else
# 64-bit OS, and we target 32-bit cross compilation
ifeq ($(i386),1)
NVCCFLAGS += -m32
LIB_ARCH = i386
ifneq ($(DARWIN),)
CXX_ARCH_FLAGS += -arch i386
else
CXX_ARCH_FLAGS += -m32
endif
else
ifneq ($(SNOWLEOPARD),)
NVCCFLAGS += -m32
CXX_ARCH_FLAGS += -arch i386 -m32
LIB_ARCH = i386
endif
endif
endif

The i386 or x86_64 environment variables are not set anywhere within the Makefile, therefore this Makefile expects them to be manually set. The last part of the code evaluates $SNOWLEOPARD which is set within the Makefile, it just doesn’t seem to be properly set since it is an empty string on my system.

Here are a few ways to fix the compilation error:

1) Set the i386 environment variable when running make using ‘make i386=1‘ (make sure to clean up the code first using ‘make clobber‘ in order to remove libraries which were compiled for the wrong architecture). This will ensure that the -m32 compilation flag is used, you just need to remember setting i386 every time.

2) For a permanent fix edit ‘common.mk’ and force the usage of -m32 by replacing the above code with:

NVCCFLAGS += -m32
LIB_ARCH = i386
CXX_ARCH_FLAGS += -arch i386 -m32

3) Forcing $SNOWLEOPARD to a non null string in the Makefile should work as well.