docs/6 - Toolchain types.txt
author "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>
Sat Aug 14 16:37:11 2010 +0200 (2010-08-14)
changeset 2076 b58109b7b321
child 2563 e17f35b05539
permissions -rw-r--r--
docs: split into multiple files

The overview.txt file has evolved into more than just an overview.
Split it into chapters, and include the misc tutorials.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>
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File.........: 6 - Toolchain types.txt
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Copyrigth....: (C) 2010 Yann E. MORIN <yann.morin.1998@anciens.enib.fr>
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License......: Creative Commons Attribution Share Alike (CC-by-sa), v2.5
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Toolchain types  /
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________________/
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There are four kinds of toolchains you could encounter.
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First off, you must understand the following: when it comes to compilers there
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are up to four machines involved:
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  1) the machine configuring the toolchain components: the config machine
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  2) the machine building the toolchain components:    the build machine
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  3) the machine running the toolchain:                the host machine
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  4) the machine the toolchain is generating code for: the target machine
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We can most of the time assume that the config machine and the build machine
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are the same. Most of the time, this will be true. The only time it isn't
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is if you're using distributed compilation (such as distcc). Let's forget
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this for the sake of simplicity.
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So we're left with three machines:
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 - build
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 - host
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 - target
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Any toolchain will involve those three machines. You can be as pretty sure of
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this as "2 and 2 are 4". Here is how they come into play:
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1) build == host == target
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    This is a plain native toolchain, targetting the exact same machine as the
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    one it is built on, and running again on this exact same machine. You have
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    to build such a toolchain when you want to use an updated component, such
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    as a newer gcc for example.
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    crosstool-NG calls it "native".
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2) build == host != target
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    This is a classic cross-toolchain, which is expected to be run on the same
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    machine it is compiled on, and generate code to run on a second machine,
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    the target.
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    crosstool-NG calls it "cross".
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3) build != host == target
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    Such a toolchain is also a native toolchain, as it targets the same machine
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    as it runs on. But it is build on another machine. You want such a
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    toolchain when porting to a new architecture, or if the build machine is
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    much faster than the host machine.
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    crosstool-NG calls it "cross-native".
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4) build != host != target
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    This one is called a canadian-toolchain (*), and is tricky. The three
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    machines in play are different. You might want such a toolchain if you
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    have a fast build machine, but the users will use it on another machine,
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    and will produce code to run on a third machine.
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    crosstool-NG calls it "canadian".
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crosstool-NG can build all these kinds of toolchains (or is aiming at it,
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anyway!)
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(*) The term Canadian Cross came about because at the time that these issues
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    were all being hashed out, Canada had three national political parties.
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    http://en.wikipedia.org/wiki/Cross_compiler