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Adding GLEP 47: Creating 'safe' environment variables

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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
195 [[ -z ${CHOST} ]] &amp;&amp; echo need chost
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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