Note that this question pertains specifically to Xcode 4, though additional information about other versions of Xcode are welcome.
Part 4 of this tutorial at Cocoa Factory recommends generating object code with
nasm-2.09.10 -f macho64 hello64.asm
(after putting nasm-2.09.10 in /usr/bin)
and linking it with
gcc -m64 -mmacosx-version-min=10.6 -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.7.sdk -o hello64 hello64.o
and that's just fine, but I don't want to do my compiling/linking at the command line, I'd like to just click Build and Run and have it all done for me. I imagine there must be some way to get Xcode to use those commands to compile my source when I Build, but how?