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1 @c Copyright (C) 2001-2020 Free Software Foundation, Inc.
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2 @c This is part of the GCC manual.
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3 @c For copying conditions, see the file gcc.texi.
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4
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5 @node Configure Terms
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6 @section Configure Terms and History
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7 @cindex configure terms
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8 @cindex canadian
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9
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10 The configure and build process has a long and colorful history, and can
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11 be confusing to anyone who doesn't know why things are the way they are.
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12 While there are other documents which describe the configuration process
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13 in detail, here are a few things that everyone working on GCC should
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14 know.
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15
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16 There are three system names that the build knows about: the machine you
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17 are building on (@dfn{build}), the machine that you are building for
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18 (@dfn{host}), and the machine that GCC will produce code for
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19 (@dfn{target}). When you configure GCC, you specify these with
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20 @option{--build=}, @option{--host=}, and @option{--target=}.
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21
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22 Specifying the host without specifying the build should be avoided, as
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23 @command{configure} may (and once did) assume that the host you specify
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24 is also the build, which may not be true.
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25
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26 If build, host, and target are all the same, this is called a
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27 @dfn{native}. If build and host are the same but target is different,
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28 this is called a @dfn{cross}. If build, host, and target are all
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29 different this is called a @dfn{canadian} (for obscure reasons dealing
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30 with Canada's political party and the background of the person working
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31 on the build at that time). If host and target are the same, but build
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32 is different, you are using a cross-compiler to build a native for a
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33 different system. Some people call this a @dfn{host-x-host},
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34 @dfn{crossed native}, or @dfn{cross-built native}. If build and target
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35 are the same, but host is different, you are using a cross compiler to
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36 build a cross compiler that produces code for the machine you're
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37 building on. This is rare, so there is no common way of describing it.
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38 There is a proposal to call this a @dfn{crossback}.
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39
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40 If build and host are the same, the GCC you are building will also be
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41 used to build the target libraries (like @code{libstdc++}). If build and host
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42 are different, you must have already built and installed a cross
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43 compiler that will be used to build the target libraries (if you
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44 configured with @option{--target=foo-bar}, this compiler will be called
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45 @command{foo-bar-gcc}).
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46
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47 In the case of target libraries, the machine you're building for is the
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48 machine you specified with @option{--target}. So, build is the machine
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49 you're building on (no change there), host is the machine you're
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50 building for (the target libraries are built for the target, so host is
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51 the target you specified), and target doesn't apply (because you're not
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52 building a compiler, you're building libraries). The configure/make
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53 process will adjust these variables as needed. It also sets
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54 @code{$with_cross_host} to the original @option{--host} value in case you
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55 need it.
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56
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57 The @code{libiberty} support library is built up to three times: once
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58 for the host, once for the target (even if they are the same), and once
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59 for the build if build and host are different. This allows it to be
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60 used by all programs which are generated in the course of the build
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61 process.
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