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Adding GLEP 47: Creating 'safe' environment variables

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27     <div class="document">
28     <table class="rfc2822 field-list" frame="void" rules="none">
29     <col class="field-name" />
30     <col class="field-body" />
31     <tbody valign="top">
32     <tr class="field"><th class="field-name">GLEP:</th><td class="field-body">47</td>
33     </tr>
34     <tr class="field"><th class="field-name">Title:</th><td class="field-body">Creating 'safe' environment variables</td>
35     </tr>
36     <tr class="field"><th class="field-name">Version:</th><td class="field-body">1.8</td>
37     </tr>
38     <tr class="field"><th class="field-name">Last-Modified:</th><td class="field-body"><a class="reference" href="http://www.gentoo.org/cgi-bin/viewcvs/xml/htdocs/proj/en/glep/glep-0047.txt?cvsroot=gentoo">2006/01/26 20:56:55</a></td>
39     </tr>
40     <tr class="field"><th class="field-name">Author:</th><td class="field-body">Diego Pettenò, Fabian rroffen &lt;{flameeyes,grobian}&#64;gentoo.org&gt;</td>
41     </tr>
42     <tr class="field"><th class="field-name">Status:</th><td class="field-body">Active</td>
43     </tr>
44     <tr class="field"><th class="field-name">Type:</th><td class="field-body">Proposal</td>
45     </tr>
46     <tr class="field"><th class="field-name">Content-Type:</th><td class="field-body"><a class="reference" href="glep-0012.html">text/x-rst</a></td>
47     </tr>
48     <tr class="field"><th class="field-name">Created:</th><td class="field-body">14-Oct-2005</td>
49     </tr>
50     <tr class="field"><th class="field-name">Post-History:</th><td class="field-body"></td>
51     </tr>
52     </tbody>
53     </table>
54     <hr />
55     <div class="contents topic" id="contents">
56     <p class="topic-title first"><a name="contents">Contents</a></p>
57     <ul class="simple">
58     <li><a class="reference" href="#credits" id="id9" name="id9">Credits</a></li>
59     <li><a class="reference" href="#abstract" id="id10" name="id10">Abstract</a></li>
60     <li><a class="reference" href="#motivation" id="id11" name="id11">Motivation</a></li>
61     <li><a class="reference" href="#rationale" id="id12" name="id12">Rationale</a></li>
62     <li><a class="reference" href="#backwards-compatibility" id="id13" name="id13">Backwards Compatibility</a></li>
63     <li><a class="reference" href="#specification" id="id14" name="id14">Specification</a><ul>
64     <li><a class="reference" href="#variables" id="id15" name="id15">Variables</a></li>
65     </ul>
66     </li>
67     <li><a class="reference" href="#references" id="id16" name="id16">References</a></li>
68     <li><a class="reference" href="#copyright" id="id17" name="id17">Copyright</a></li>
69     </ul>
70     </div>
71     <div class="section" id="credits">
72     <h1><a class="toc-backref" href="#id9" name="credits">Credits</a></h1>
73     <p>The text of this GLEP is a result of a discussion and input of the
74     following persons, in no particular order: Mike Frysinger, Diego
75     Pettenò, Fabian Groffen and Finn Thain.</p>
76     </div>
77     <div class="section" id="abstract">
78     <h1><a class="toc-backref" href="#id10" name="abstract">Abstract</a></h1>
79     <p>In order for ebuilds and eclasses to be able to make host specific
80     decisions, it is necessary to have a number of environmental variables
81     which allow for such decisions. This GLEP introduces some measures that
82     need to be made to make these decisions 'safe', by making sure the
83     variables the decisions are based on are 'safe'. A small overlap with
84     GLEP 22 <a class="footnote-reference" href="#id5" id="id1" name="id1">[1]</a> is being handled in this GLEP where the use of 2-tuple
85     keywords are being kept instead of 4-tuple keywords. Additionally, the
86     <tt class="literal"><span class="pre">ELIBC</span></tt>, <tt class="literal"><span class="pre">KERNEL</span></tt> and <tt class="literal"><span class="pre">ARCH</span></tt> get auto filled starting from
87     <tt class="literal"><span class="pre">CHOST</span></tt> and the 2-tuple keyword, instead of solely from they 4-tuple
88     keyword as proposed in GLEP 22.</p>
89     <p>The destiny of the <tt class="literal"><span class="pre">USERLAND</span></tt> variable is out of the scope of this
90     GLEP. Depending on its presence in the tree, it may be decided to set
91     this variable the same way we propose to set <tt class="literal"><span class="pre">ELIBC</span></tt>, <tt class="literal"><span class="pre">KERNEL</span></tt> and
92     <tt class="literal"><span class="pre">ARCH</span></tt>, or alternatively, e.g. via the profiles.</p>
93     </div>
94     <div class="section" id="motivation">
95     <h1><a class="toc-backref" href="#id11" name="motivation">Motivation</a></h1>
96     <p>The Gentoo/Alt project is in an emerging state to get ready to serve a
97     plethora of 'alternative' configurations such as FreeBSD, NetBSD,
98     DragonflyBSD, GNU/kFreeBSD, Mac OS X, (Open)Darwin, (Open)Solaris and so
99     on. As such, the project is in need for a better grip on the actual
100     host being built on. This information on the host environment is
101     necessary to make proper (automated) decisions on settings that are
102     highly dependant on the build environment, such as platform or as in
103     <a class="footnote-reference" href="#id6" id="id2" name="id2">[2]</a>.</p>
104     </div>
105     <div class="section" id="rationale">
106     <h1><a class="toc-backref" href="#id12" name="rationale">Rationale</a></h1>
107     <p>Gentoo's unique Portage system allows easy installation of applications
108     from source packages. Compiling sources is prone to many environmental
109     settings and availability of certain tools. Only recently the Gentoo
110     for FreeBSD project has started, as second Gentoo project that operates
111     on a foreign host operating system using foreign (non-GNU) C-libraries
112     and userland utilities. Such projects suffer from the current implicit
113     assumption made within Gentoo Portage's ebuilds that there is a single
114     type of operating system, C-libraries and system utilities. In order to
115     enable ebuilds -- and also eclasses -- to be aware of these
116     environmental differences, information regarding it should be supplied.
117     Since decisions based on this information can be vital, it is of high
118     importance that this information can be trusted and the values can be
119     considered 'safe' and correct.</p>
120     </div>
121     <div class="section" id="backwards-compatibility">
122     <h1><a class="toc-backref" href="#id13" name="backwards-compatibility">Backwards Compatibility</a></h1>
123     <p>The proposed keywording scheme in this GLEP is fully compatible with the
124     current situation of the portage tree, this in contrast to GLEP 22. The
125     variables provided by GLEP 22 can't be extracted from the new keyword,
126     but since GLEP 22-style keywords aren't in the tree at the moment, that
127     is not a problem. The same information can be extracted from the CHOST
128     variable, if necessary. No modifications to ebuilds will have to be
129     made.</p>
130     </div>
131     <div class="section" id="specification">
132     <h1><a class="toc-backref" href="#id14" name="specification">Specification</a></h1>
133     <p>Unlike GLEP 22 the current keyword scheme as used in practice is not
134     changed. Instead of proposing a 4-tuple <a class="footnote-reference" href="#id7" id="id3" name="id3">[3]</a> keyword, a 2-tuple
135     keyword is chosen for archs that require them. Archs for which a
136     1-tuple keyword suffices, keep that keyword. Since this doesn't change
137     anything to the current situation in the tree, it is considered to be a
138     big advantage over the 4-tuple keyword from GLEP 22. This GLEP is an
139     official specification of the syntax of the keyword.</p>
140     <p>Keywords will consist out of two parts separated by a hyphen ('-'). The
141     left hand part of the keyword 2-tuple is the architecture, such as
142     ppc64, sparc and x86. The right hand part indicates the operating
143     system or distribution, such as linux, macos, darwin, obsd, etc. If the
144     right hand part is omitted, it implies the operating system/distribution
145     type is GNU/Linux. In such case the hyphen is also omitted. Examples
146     of such keywords are ppc-darwin and x86. This is fully compatible with
147     the current keywords used in the tree.</p>
148     <p>The variables <tt class="literal"><span class="pre">ELIBC</span></tt>, <tt class="literal"><span class="pre">KERNEL</span></tt> and <tt class="literal"><span class="pre">ARCH</span></tt> are currently set in
149     the profiles when other than their defaults for a GNU/Linux system.
150     They can as such easily be overridden and defined by the user. To
151     prevent this from happening, the variables should be auto filled by
152     Portage itself, based on the <tt class="literal"><span class="pre">CHOST</span></tt> variable.</p>
153     <p>A map file can be used to have the various <tt class="literal"><span class="pre">CHOST</span></tt> values being
154     translated to the correct values for the four variables. This change is
155     invisible for ebuilds and eclasses, but allows to rely on these
156     variables as they are based on a 'safe' value -- the <tt class="literal"><span class="pre">CHOST</span></tt> variable.
157     Ebuilds should not be sensitive to the keyword value, but use the
158     aforementioned four variables instead. They allow specific tests for
159     properties. If this is undesirable, the full <tt class="literal"><span class="pre">CHOST</span></tt> variable can be
160     used to match a complete operating system.</p>
161     <p>Current USE-expansion is being maintained, for backwards compatibility.
162     Since the expansion is based on the variables mentioned above which do
163     not change, but only in the way they are generated, there should be no
164     problem in maintaining them.</p>
165     <div class="section" id="variables">
166     <h2><a class="toc-backref" href="#id15" name="variables">Variables</a></h2>
167     <p>The <tt class="literal"><span class="pre">ELIBC</span></tt>, <tt class="literal"><span class="pre">KERNEL</span></tt>, <tt class="literal"><span class="pre">ARCH</span></tt> variables are filled from a profile
168     file. The file can be overlaid, such that the following entries in the
169     map file (on the left of the arrow) will result in the assigned
170     variables on the right hand side of the arrow:</p>
171     <pre class="literal-block">
172     *-*-linux-* -&gt; KERNEL=&quot;linux&quot;
173     *-*-*-gnu -&gt; ELIBC=&quot;glibc&quot;
174     *-*-kfreebsd-gnu -&gt; KERNEL=&quot;FreeBSD&quot; ELIBC=&quot;glibc&quot;
175     *-*-freebsd* -&gt; KERNEL=&quot;FreeBSD&quot; ELIBC=&quot;FreeBSD&quot;
176     *-*-darwin* -&gt; KERNEL=&quot;Darwin&quot; ELIBC=&quot;Darwin&quot;
177     *-*-netbsd* -&gt; KERNEL=&quot;NetBSD&quot; ELIBC=&quot;NetBSD&quot;
178     *-*-solaris* -&gt; KERNEL=&quot;Solaris&quot; ELIBC=&quot;Solaris&quot;
179     </pre>
180     <p>A way to achieve this is proposed by Mike Frysinger <a class="footnote-reference" href="#id8" id="id4" name="id4">[4]</a>, which
181     suggests to have a env-map file, for instance filled with:</p>
182     <pre class="literal-block">
183     % cat env-map
184     *-linux-* KERNEL=linux
185     *-gnu ELIBC=glibc
186     x86_64-* ARCH=amd64
187     </pre>
188     <p>then the following bash script can be used to set the four variables to
189     their correct values:</p>
190     <pre class="literal-block">
191     % cat readmap
192     #!/bin/bash
194     CBUILD=${CBUILD:-${CHOST=${CHOST:-$1}}}
195     [[ -z ${CHOST} ]] &amp;&amp; echo need chost
197     unset KERNEL ELIBC ARCH
199     while read LINE ; do
200     set -- ${LINE}
201     targ=$1
202     shift
203     [[ ${CBUILD} == ${targ} ]] &amp;&amp; eval $&#64;
204     done &lt; env-map
207     </pre>
208     <p>Given the example env-map file, this script would result in:</p>
209     <pre class="literal-block">
210     % ./readmap x86_64-pc-linux-gnu
211     ARCH=amd64 KERNEL=linux ELIBC=glibc
212     </pre>
213     <p>It should be noted, however, that the bash script is a proof of concept
214     implementation. It cannot be used as Portage will need this
215     information, which is written in Python. Hence, an equivalent of this
216     bash script should be written in Python to be able to use it within
217     Portage. This is considered to be a non-issue coding wise.</p>
218     </div>
219     </div>
220     <div class="section" id="references">
221     <h1><a class="toc-backref" href="#id16" name="references">References</a></h1>
222     <table class="footnote" frame="void" id="id5" rules="none">
223     <colgroup><col class="label" /><col /></colgroup>
224     <tbody valign="top">
225     <tr><td class="label"><a class="fn-backref" href="#id1" name="id5">[1]</a></td><td>GLEP 22, New &quot;keyword&quot; system to incorporate various
226     userlands/kernels/archs, Goodyear,
227     (<a class="reference" href="http://glep.gentoo.org/glep-0022.html">http://glep.gentoo.org/glep-0022.html</a>)</td></tr>
228     </tbody>
229     </table>
230     <table class="footnote" frame="void" id="id6" rules="none">
231     <colgroup><col class="label" /><col /></colgroup>
232     <tbody valign="top">
233     <tr><td class="label"><a class="fn-backref" href="#id2" name="id6">[2]</a></td><td><p>For example in the perl ebuild, it is necessary to
234     fill in the C-library part, which on a FreeBSD system is other than
235     on a Linux system and currently is handled as follows:</p>
236     <pre class="literal-block">
237     [[ ${ELIBC} == &quot;FreeBSD&quot; ]] &amp;&amp; myconf=&quot;${myconf} -Dlibc=/usr/lib/libc.a&quot;
238     </pre>
239     </td></tr>
240     </tbody>
241     </table>
242     <table class="footnote" frame="void" id="id7" rules="none">
243     <colgroup><col class="label" /><col /></colgroup>
244     <tbody valign="top">
245     <tr><td class="label"><a class="fn-backref" href="#id3" name="id7">[3]</a></td><td>For the purpose of readability, we will refer to 1, 2 and
246     4-tuples, even though tuple in itself suggest a field consisting of
247     two values. For clarity: a 1-tuple describes a single value field,
248     while a 4-tuple decribes a field consisting out of four values.</td></tr>
249     </tbody>
250     </table>
251     <table class="footnote" frame="void" id="id8" rules="none">
252     <colgroup><col class="label" /><col /></colgroup>
253     <tbody valign="top">
254     <tr><td class="label"><a class="fn-backref" href="#id4" name="id8">[4]</a></td><td><a class="reference" href="mailto:vapier">mailto:vapier</a> [at) gentoo .dot org</td></tr>
255     </tbody>
256     </table>
257     </div>
258     <div class="section" id="copyright">
259     <h1><a class="toc-backref" href="#id17" name="copyright">Copyright</a></h1>
260     <p>This document has been placed in the public domain.</p>
261     </div>
262     </div>
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