The clang executable size mystery deepens: The sizes are indeed waaaay big: 7.4M test-files-clang/test* 4.5M test-files-clang/test-stripped* 1.4M test-files-gcc/test* 1.1M test-files-gcc/test-stripped* Looking at the load info from the stripped versions, it is all in the main text segment: test-files-clang/load test-files-gcc/load __TEXT.__text : 3,554,134 833,502 __TEXT.__stubs : 876 672 __TEXT.__stub_helper : 1,476 1,136 __TEXT.__const : 59,040 32,104 __TEXT.__cstring : 24,156 24,900 __TEXT.__dof_HaskellEv : 4,774 4,774 __TEXT.__eh_frame : 22,976 46,664 __DATA.__got : 1,264 880 __DATA.__nl_symbol_ptr : 16 16 __DATA.__la_symbol_ptr : 1,168 896 __DATA.__mod_init_func : 8 8 __DATA.__const : 130,048 79,744 __DATA.__data : 231,848 22,904 __DATA.__common : 45,924 46,092 __DATA.__bss : 856 840 TOTAL SIZE : 4,078,564 1,095,132 But, the compiled sizes are identical: 1.9K test-files-clang/Main.o 1.9K test-files-gcc/Main.o And, after dumping the link command, and looking up all the libs linked in (identical set in both cases), the clang libs are actually *smaller:* 13,004,272 ...clang.../lib/ghc-7.8.3/base-4.7.0.1/libHSbase-4.7.0.1.a 792,352 ...clang.../lib/ghc-7.8.3/ghc-prim-0.3.1.0/libHSghc-prim-0.3.1.0.a 1,010,824 ...clang.../lib/ghc-7.8.3/integer-gmp-0.5.1.0/libHSinteger-gmp-0.5.1.0.a 55,816 ...clang.../lib/ghc-7.8.3/rts-1.0/libCffi.a 565,112 ...clang.../lib/ghc-7.8.3/rts-1.0/libHSrts.a 24,378,416 ...gcc.../lib/ghc-7.8.3/base-4.7.0.1/libHSbase-4.7.0.1.a 1,253,176 ...gcc.../lib/ghc-7.8.3/ghc-prim-0.3.1.0/libHSghc-prim-0.3.1.0.a 1,014,280 ...gcc.../lib/ghc-7.8.3/integer-gmp-0.5.1.0/libHSinteger-gmp-0.5.1.0.a 57,984 ...gcc.../lib/ghc-7.8.3/rts-1.0/libCffi.a 556,432 ...gcc.../lib/ghc-7.8.3/rts-1.0/libHSrts.a So now I'm totally mystified! What is in that 3M of extra text segment?!?!? - Mark