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Date:      Wed, 17 Oct 2012 05:26:21 -0500 (CDT)
From:      Scott Bennett <>
Subject:   Re: clang options question
Message-ID:  <>

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     On Wed, 17 Oct 2012 04:25:14 +1100 andrew clarke <>
>On Tue 2012-10-16 10:52:36 UTC-0500, Scott Bennett ( wrote:
>> From looking at the clang(1) man page, it is not clear to me what the
>> difference is between the -arch option and the -march= option.  Would
>> someone please summarize the difference(s) for me?  Thanks much!
>>From the users POV, clang is supposed to be a drop-in replacement for
>gcc, where -arch is also an option. Looking online though, it would
>appear it's an Apple Darwin (OS X) only feature of gcc for generating
>universal binaries.

     Oh.  Okay.  Thanks for the Darwin info, too.  I hadn't known that
OS X had carried on NEXTSTEP's support for fat binaries.
>The question is a bit academic as it doesn't actually do anything in
>FreeBSD, at least not for me:
>$ clang -o hello -arch x86_64 hello.c
>clang: warning: argument unused during compilation: '-arch x86_64'
>$ clang -v
>clang version 3.1 (branches/release_31)
>Target: amd64-portbld-freebsd8.3
>Thread model: posix
>Nor in Linux (an old version, admittedly):
>$ clang -o hello -arch i386 hello.c
>clang: warning: argument unused during compilation: '-arch i386'
>$ clang -v
>clang version 1.1 (branches/release_27)
>Target: x86_64-pc-linux-gnu
>Thread model: posix
     I see.  So it's just decoration for compatibility with gcc and
something to worry about.  Thanks very much for the response.

                                  Scott Bennett, Comm. ASMELG, CFIAG
* Internet:       bennett at                              *
* "A well regulated and disciplined militia, is at all times a good  *
* objection to the introduction of that bane of all free governments *
* -- a standing army."                                               *
*    -- Gov. John Hancock, New York Journal, 28 January 1790         *

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