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@@ -1,225 +1,218 @@
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<?xml version="1.0" encoding="ISO-8859-1"?>
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-<!DOCTYPE sect1 PUBLIC "-//OASIS//DTD DocBook XML V4.4//EN" "http://www.oasis-open.org/docbook/xml/4.4/docbookx.dtd" [
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+<!DOCTYPE sect1 PUBLIC "-//OASIS//DTD DocBook XML V4.4//EN"
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+ "http://www.oasis-open.org/docbook/xml/4.4/docbookx.dtd" [
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<!ENTITY % general-entities SYSTEM "../general.ent">
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%general-entities;
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]>
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+
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<sect1 id="ch-tools-toolchaintechnotes">
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-<title>Toolchain Technical Notes</title>
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-<?dbhtml filename="toolchaintechnotes.html"?>
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-
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-<para>This section explains some of the rationale and technical
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-details behind the overall build method. It is not essential to
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-immediately understand everything in this section. Most of this
|
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-information will be clearer after performing an actual build. This
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-section can be referred back to at any time during the process.</para>
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-
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-<para>The overall goal of <xref linkend="chapter-temporary-tools"/> is to
|
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-provide a temporary environment that can be chrooted into and from which can be
|
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|
-produced a clean, trouble-free build of the target LFS system in <xref
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-linkend="chapter-building-system"/>. Along the way, we separate the new system
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-from the host system as much as possible, and in doing so, build a
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-self-contained and self-hosted toolchain. It should be noted that the build
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-process has been designed to minimize the risks for new readers and provide
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-maximum educational value at the same time.</para>
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-
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-<important>
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-<para>Before continuing, be aware of the name of the working platform,
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-often referred to as the target triplet. Many times, the target
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-triplet will probably be <emphasis>i686-pc-linux-gnu</emphasis>. A
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-simple way to determine the name of the target triplet is to run the
|
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-<command>config.guess</command> script that comes with the source for
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-many packages. Unpack the Binutils sources and run the script:
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-<userinput>./config.guess</userinput> and note the output.</para>
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-
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-<para>Also be aware of the name of the platform's dynamic linker,
|
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-often referred to as the dynamic loader (not to be confused with the
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-standard linker <command>ld</command> that is part of Binutils). The
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-dynamic linker provided by Glibc finds and loads the shared libraries
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-needed by a program, prepares the program to run, and then runs it.
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-The name of the dynamic linker will usually be
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-<filename class="libraryfile">ld-linux.so.2</filename>. On platforms that are less
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-prevalent, the name might be <filename class="libraryfile">ld.so.1</filename>,
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-and newer 64 bit platforms might be named something else entirely. The name of
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-the platform's dynamic linker can be determined by looking in the
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-<filename class="directory">/lib</filename> directory on the host
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-system. A sure-fire way to determine the name is to inspect a random
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-binary from the host system by running: <userinput>readelf -l <name
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-of binary> | grep interpreter</userinput> and noting the output.
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-The authoritative reference covering all platforms is in the
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-<filename>shlib-versions</filename> file in the root of the Glibc
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-source tree.</para>
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-</important>
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-
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-<para>Some key technical points of how the <xref linkend="chapter-temporary-tools"/> build
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-method works:</para>
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-
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-<itemizedlist>
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-<listitem><para>The process is similar in principle to
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-cross-compiling, whereby tools installed in the same prefix work in
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-cooperation, and thus utilize a little GNU
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-<quote>magic</quote></para></listitem>
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-
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-<listitem><para>Careful manipulation of the standard linker's library
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-search path ensures programs are linked only against chosen
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-libraries</para></listitem>
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-
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-<listitem><para>Careful manipulation of <command>gcc</command>'s
|
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-<filename>specs</filename> file tells the compiler which target dynamic
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-linker will be used</para></listitem>
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-</itemizedlist>
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-
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-<para>Binutils is installed first because the
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-<command>configure</command> runs of both GCC and Glibc perform
|
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|
-various feature tests on the assembler and linker to determine which
|
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-software features to enable or disable. This is more important than
|
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|
-one might first realize. An incorrectly configured GCC or Glibc can
|
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|
-result in a subtly broken toolchain, where the impact of such breakage
|
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|
-might not show up until near the end of the build of an entire
|
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|
-distribution. A test suite failure will usually highlight this error
|
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|
-before too much additional work is performed.</para>
|
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-
|
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-<para>Binutils installs its assembler and linker in two locations,
|
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|
-<filename class="directory">/tools/bin</filename> and <filename
|
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|
-class="directory">/tools/$TARGET_TRIPLET/bin</filename>. The tools in
|
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-one location are hard linked to the other. An important facet of the
|
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|
-linker is its library search order. Detailed information can be
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|
-obtained from <command>ld</command> by passing it the
|
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|
-<parameter>--verbose</parameter> flag. For example, an <userinput>ld
|
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---verbose | grep SEARCH</userinput> will illustrate the current search
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-paths and their order. It shows which files are linked by
|
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-<command>ld</command> by compiling a dummy program and passing the
|
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-<parameter>--verbose</parameter> switch to the linker. For example,
|
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-<userinput>gcc dummy.c -Wl,--verbose 2>&1 | grep
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-succeeded</userinput> will show all the files successfully opened
|
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|
-during the linking.</para>
|
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-
|
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-<para>The next package installed is GCC. An example of what can be
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-seen during its run of <command>configure</command> is:</para>
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-
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-<screen><computeroutput>checking what assembler to use...
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+ <?dbhtml filename="toolchaintechnotes.html"?>
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+
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+ <title>Toolchain Technical Notes</title>
|
|
|
+
|
|
|
+ <para>This section explains some of the rationale and technical details
|
|
|
+ behind the overall build method. It is not essential to immediately
|
|
|
+ understand everything in this section. Most of this information will be
|
|
|
+ clearer after performing an actual build. This section can be referred
|
|
|
+ back to at any time during the process.</para>
|
|
|
+
|
|
|
+ <para>The overall goal of <xref linkend="chapter-temporary-tools"/> is to
|
|
|
+ provide a temporary environment that can be chrooted into and from which can be
|
|
|
+ produced a clean, trouble-free build of the target LFS system in <xref
|
|
|
+ linkend="chapter-building-system"/>. Along the way, we separate the new system
|
|
|
+ from the host system as much as possible, and in doing so, build a
|
|
|
+ self-contained and self-hosted toolchain. It should be noted that the build
|
|
|
+ process has been designed to minimize the risks for new readers and provide
|
|
|
+ maximum educational value at the same time.</para>
|
|
|
+
|
|
|
+ <important>
|
|
|
+ <para>Before continuing, be aware of the name of the working platform,
|
|
|
+ often referred to as the target triplet. Many times, the target
|
|
|
+ triplet will probably be <emphasis>i686-pc-linux-gnu</emphasis>. A
|
|
|
+ simple way to determine the name of the target triplet is to run the
|
|
|
+ <command>config.guess</command> script that comes with the source for
|
|
|
+ many packages. Unpack the Binutils sources and run the script:
|
|
|
+ <userinput>./config.guess</userinput> and note the output.</para>
|
|
|
+
|
|
|
+ <para>Also be aware of the name of the platform's dynamic linker, often
|
|
|
+ referred to as the dynamic loader (not to be confused with the standard
|
|
|
+ linker <command>ld</command> that is part of Binutils). The dynamic linker
|
|
|
+ provided by Glibc finds and loads the shared libraries needed by a program,
|
|
|
+ prepares the program to run, and then runs it. The name of the dynamic
|
|
|
+ linker will usually be <filename class="libraryfile">ld-linux.so.2</filename>.
|
|
|
+ On platforms that are less prevalent, the name might be <filename
|
|
|
+ class="libraryfile">ld.so.1</filename>, and newer 64 bit platforms might
|
|
|
+ be named something else entirely. The name of the platform's dynamic linker
|
|
|
+ can be determined by looking in the <filename class="directory">/lib</filename>
|
|
|
+ directory on the host system. A sure-fire way to determine the name is to
|
|
|
+ inspect a random binary from the host system by running:
|
|
|
+ <userinput>readelf -l <name of binary> | grep interpreter</userinput>
|
|
|
+ and noting the output. The authoritative reference covering all platforms
|
|
|
+ is in the <filename>shlib-versions</filename> file in the root of the Glibc
|
|
|
+ source tree.</para>
|
|
|
+ </important>
|
|
|
+
|
|
|
+ <para>Some key technical points of how the <xref
|
|
|
+ linkend="chapter-temporary-tools"/> build method works:</para>
|
|
|
+
|
|
|
+ <itemizedlist>
|
|
|
+ <listitem>
|
|
|
+ <para>The process is similar in principle to cross-compiling, whereby
|
|
|
+ tools installed in the same prefix work in cooperation, and thus utilize
|
|
|
+ a little GNU <quote>magic</quote></para>
|
|
|
+ </listitem>
|
|
|
+ <listitem>
|
|
|
+ <para>Careful manipulation of the standard linker's library search path
|
|
|
+ ensures programs are linked only against chosen libraries</para>
|
|
|
+ </listitem>
|
|
|
+ <listitem>
|
|
|
+ <para>Careful manipulation of <command>gcc</command>'s
|
|
|
+ <filename>specs</filename> file tells the compiler which target dynamic
|
|
|
+ linker will be used</para>
|
|
|
+ </listitem>
|
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|
+ </itemizedlist>
|
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+
|
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|
+ <para>Binutils is installed first because the <command>configure</command>
|
|
|
+ runs of both GCC and Glibc perform various feature tests on the assembler
|
|
|
+ and linker to determine which software features to enable or disable. This
|
|
|
+ is more important than one might first realize. An incorrectly configured
|
|
|
+ GCC or Glibc can result in a subtly broken toolchain, where the impact of
|
|
|
+ such breakage might not show up until near the end of the build of an
|
|
|
+ entire distribution. A test suite failure will usually highlight this error
|
|
|
+ before too much additional work is performed.</para>
|
|
|
+
|
|
|
+ <para>Binutils installs its assembler and linker in two locations,
|
|
|
+ <filename class="directory">/tools/bin</filename> and <filename
|
|
|
+ class="directory">/tools/$TARGET_TRIPLET/bin</filename>. The tools in one
|
|
|
+ location are hard linked to the other. An important facet of the linker is
|
|
|
+ its library search order. Detailed information can be obtained from
|
|
|
+ <command>ld</command> by passing it the <parameter>--verbose</parameter>
|
|
|
+ flag. For example, an <userinput>ld --verbose | grep SEARCH</userinput>
|
|
|
+ will illustrate the current search paths and their order. It shows which
|
|
|
+ files are linked by <command>ld</command> by compiling a dummy program and
|
|
|
+ passing the <parameter>--verbose</parameter> switch to the linker. For example,
|
|
|
+ <userinput>gcc dummy.c -Wl,--verbose 2>&1 | grep succeeded</userinput>
|
|
|
+ will show all the files successfully opened during the linking.</para>
|
|
|
+
|
|
|
+ <para>The next package installed is GCC. An example of what can be
|
|
|
+ seen during its run of <command>configure</command> is:</para>
|
|
|
+
|
|
|
+<screen><computeroutput>checking what assembler to use...
|
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|
/tools/i686-pc-linux-gnu/bin/as
|
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|
checking what linker to use... /tools/i686-pc-linux-gnu/bin/ld</computeroutput></screen>
|
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|
|
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|
-<para>This is important for the reasons mentioned above. It also
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-demonstrates that GCC's configure script does not search the PATH
|
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-directories to find which tools to use. However, during the actual
|
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|
-operation of <command>gcc</command> itself, the same
|
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|
-search paths are not necessarily used. To find out which standard
|
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-linker <command>gcc</command> will use, run: <userinput>gcc
|
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--print-prog-name=ld</userinput>.</para>
|
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-
|
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|
-<para>Detailed information can be obtained from <command>gcc</command>
|
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|
-by passing it the <parameter>-v</parameter> command line option while
|
|
|
-compiling a dummy program. For example, <userinput>gcc -v
|
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|
-dummy.c</userinput> will show detailed information about the
|
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|
-preprocessor, compilation, and assembly stages, including
|
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|
-<command>gcc</command>'s included search paths and their order.</para>
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-
|
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-<para>The next package installed is Glibc. The most important
|
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-considerations for building Glibc are the compiler, binary tools, and
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-kernel headers. The compiler is generally not an issue since Glibc
|
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-will always use the <command>gcc</command> found in a
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-<envar>PATH</envar> directory.
|
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-The binary tools and kernel headers can be a bit more complicated.
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-Therefore, take no risks and use the available configure switches to
|
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-enforce the correct selections. After the run of
|
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-<command>configure</command>, check the contents of the
|
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-<filename>config.make</filename> file in the <filename
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-class="directory">glibc-build</filename> directory for all important
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-details. Note the use of <parameter>CC="gcc -B/tools/bin/"</parameter>
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-to control which binary tools are used and the use of the
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-<parameter>-nostdinc</parameter> and <parameter>-isystem</parameter>
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-flags to control the compiler's include search path. These items
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-highlight an important aspect of the Glibc package—it is very
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-self-sufficient in terms of its build machinery and generally does not
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-rely on toolchain defaults.</para>
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-
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-<para>After the Glibc installation, make some adjustments to ensure
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-that searching and linking take place only within the <filename
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-class="directory">/tools</filename> prefix. Install an adjusted
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-<command>ld</command>, which has a hard-wired search path limited to
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-<filename class="directory">/tools/lib</filename>. Then amend
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-<command>gcc</command>'s specs file to point to the new dynamic linker
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-in <filename class="directory">/tools/lib</filename>. This last step
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-is vital to the whole process. As mentioned above, a hard-wired path
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-to a dynamic linker is embedded into every Executable and Link Format
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-(ELF)-shared executable. This can be inspected by running:
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-<userinput>readelf -l <name of binary> | grep
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-interpreter</userinput>. Amending gcc's specs file
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-ensures that every program compiled from here through the end of this
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-chapter will use the new dynamic linker in <filename
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-class="directory">/tools/lib</filename>.</para>
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-
|
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-<para>The need to use the new dynamic linker is also the reason why
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-the Specs patch is applied for the second pass of GCC. Failure to do
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-so will result in the GCC programs themselves having the name of the
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-dynamic linker from the host system's <filename
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-class="directory">/lib</filename> directory embedded into them, which
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-would defeat the goal of getting away from the host.</para>
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-
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-<para>During the second pass of Binutils, we are able to utilize the
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-<parameter>--with-lib-path</parameter> configure switch to control
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-<command>ld</command>'s library search path. From this point onwards,
|
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-the core toolchain is self-contained and self-hosted. The remainder of
|
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-the <xref linkend="chapter-temporary-tools"/> packages all build
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-against the new Glibc in <filename
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-class="directory">/tools</filename>.</para>
|
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-
|
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-<para>Upon entering the chroot environment in <xref
|
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|
-linkend="chapter-building-system"/>, the first major package to be
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-installed is Glibc, due to its self-sufficient nature mentioned above.
|
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-Once this Glibc is installed into <filename
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-class="directory">/usr</filename>, perform a quick changeover of the
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-toolchain defaults, then proceed in building the rest of the target
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-LFS system.</para>
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-
|
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-<!-- Removed as part of the fix for bug 1061 - we no longer build pass1
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- packages statically, therefore this explanation isn't required -->
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-
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-<!--<sect2>
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-<title>Notes on Static Linking</title>
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-
|
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-<para>Besides their specific task, most programs have to perform many
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-common and sometimes trivial operations. These include allocating
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|
-memory, searching directories, reading and writing files, string
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|
-handling, pattern matching, arithmetic, and other tasks. Instead of
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-obliging each program to reinvent the wheel, the GNU system provides
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-all these basic functions in ready-made libraries. The major library
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-on any Linux system is Glibc.</para>
|
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-
|
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-<para>There are two primary ways of linking the functions from a
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-library to a program that uses them—statically or dynamically. When
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-a program is linked statically, the code of the used functions is
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|
-included in the executable, resulting in a rather bulky program. When
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|
-a program is dynamically linked, it includes a reference to the
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-dynamic linker, the name of the library, and the name of the function,
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|
-resulting in a much smaller executable. A third option is to use the
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|
-programming interface of the dynamic linker (see <filename>dlopen(3)</filename>
|
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|
-for more information).</para>
|
|
|
-
|
|
|
-<para>Dynamic linking is the default on Linux and has three major
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-advantages over static linking. First, only one copy of the executable
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|
-library code is needed on the hard disk, instead of having multiple
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|
-copies of the same code included in several programs, thus saving
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|
-disk space. Second, when several programs use the same library
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|
-function at the same time, only one copy of the function's code is
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|
-required in core, thus saving memory space. Third, when a library
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|
-function gets a bug fixed or is otherwise improved, only the one
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|
-library needs to be recompiled instead of recompiling all programs
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|
-that make use of the improved function.</para>
|
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-
|
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|
-<para>If dynamic linking has several advantages, why then do we
|
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-statically link the first two packages in this chapter? The reasons
|
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|
-are threefold—historical, educational, and technical. The
|
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|
-historical reason is that earlier versions of LFS statically linked
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|
-every program in this chapter. Educationally, knowing the difference
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|
-between static and dynamic linking is useful. The technical benefit is
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|
-a gained element of independence from the host, meaning that those
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-programs can be used independently of the host system. However, it is
|
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|
-worth noting that an overall successful LFS build can still be
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|
-achieved when the first two packages are built dynamically.</para>
|
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|
-
|
|
|
-</sect2>-->
|
|
|
+ <para>This is important for the reasons mentioned above. It also demonstrates
|
|
|
+ that GCC's configure script does not search the PATH directories to find which
|
|
|
+ tools to use. However, during the actual operation of <command>gcc</command>
|
|
|
+ itself, the same search paths are not necessarily used. To find out which
|
|
|
+ standard linker <command>gcc</command> will use, run:
|
|
|
+ <userinput>gcc -print-prog-name=ld</userinput>.</para>
|
|
|
+
|
|
|
+ <para>Detailed information can be obtained from <command>gcc</command> by
|
|
|
+ passing it the <parameter>-v</parameter> command line option while compiling
|
|
|
+ a dummy program. For example, <userinput>gcc -v dummy.c</userinput> will show
|
|
|
+ detailed information about the preprocessor, compilation, and assembly stages,
|
|
|
+ including <command>gcc</command>'s included search paths and their order.</para>
|
|
|
+
|
|
|
+ <para>The next package installed is Glibc. The most important considerations
|
|
|
+ for building Glibc are the compiler, binary tools, and kernel headers. The
|
|
|
+ compiler is generally not an issue since Glibc will always use the
|
|
|
+ <command>gcc</command> found in a <envar>PATH</envar> directory. The binary
|
|
|
+ tools and kernel headers can be a bit more complicated. Therefore, take no
|
|
|
+ risks and use the available configure switches to enforce the correct
|
|
|
+ selections. After the run of <command>configure</command>, check the contents
|
|
|
+ of the <filename>config.make</filename> file in the <filename
|
|
|
+ class="directory">glibc-build</filename> directory for all important details.
|
|
|
+ Note the use of <parameter>CC="gcc -B/tools/bin/"</parameter> to control which
|
|
|
+ binary tools are used and the use of the <parameter>-nostdinc</parameter>
|
|
|
+ and <parameter>-isystem</parameter> flags to control the compiler's include
|
|
|
+ search path. These items highlight an important aspect of the Glibc
|
|
|
+ package—it is very self-sufficient in terms of its build machinery and
|
|
|
+ generally does not rely on toolchain defaults.</para>
|
|
|
+
|
|
|
+ <para>After the Glibc installation, make some adjustments to ensure that
|
|
|
+ searching and linking take place only within the <filename
|
|
|
+ class="directory">/tools</filename> prefix. Install an adjusted
|
|
|
+ <command>ld</command>, which has a hard-wired search path limited to
|
|
|
+ <filename class="directory">/tools/lib</filename>. Then amend
|
|
|
+ <command>gcc</command>'s specs file to point to the new dynamic linker in
|
|
|
+ <filename class="directory">/tools/lib</filename>. This last step is vital
|
|
|
+ to the whole process. As mentioned above, a hard-wired path to a dynamic
|
|
|
+ linker is embedded into every Executable and Link Format (ELF)-shared
|
|
|
+ executable. This can be inspected by running:
|
|
|
+ <userinput>readelf -l <name of binary> | grep interpreter</userinput>.
|
|
|
+ Amending gcc's specs file ensures that every program compiled from here
|
|
|
+ through the end of this chapter will use the new dynamic linker in
|
|
|
+ <filename class="directory">/tools/lib</filename>.</para>
|
|
|
+
|
|
|
+ <para>The need to use the new dynamic linker is also the reason why
|
|
|
+ the Specs patch is applied for the second pass of GCC. Failure to do
|
|
|
+ so will result in the GCC programs themselves having the name of the
|
|
|
+ dynamic linker from the host system's <filename
|
|
|
+ class="directory">/lib</filename> directory embedded into them, which
|
|
|
+ would defeat the goal of getting away from the host.</para>
|
|
|
+
|
|
|
+ <para>During the second pass of Binutils, we are able to utilize the
|
|
|
+ <parameter>--with-lib-path</parameter> configure switch to control
|
|
|
+ <command>ld</command>'s library search path. From this point onwards,
|
|
|
+ the core toolchain is self-contained and self-hosted. The remainder of
|
|
|
+ the <xref linkend="chapter-temporary-tools"/> packages all build against
|
|
|
+ the new Glibc in <filename class="directory">/tools</filename>.</para>
|
|
|
+
|
|
|
+ <para>Upon entering the chroot environment in <xref
|
|
|
+ linkend="chapter-building-system"/>, the first major package to be
|
|
|
+ installed is Glibc, due to its self-sufficient nature mentioned above.
|
|
|
+ Once this Glibc is installed into <filename
|
|
|
+ class="directory">/usr</filename>, perform a quick changeover of the
|
|
|
+ toolchain defaults, then proceed in building the rest of the target
|
|
|
+ LFS system.</para>
|
|
|
+
|
|
|
+ <!-- Removed as part of the fix for bug 1061 - we no longer build pass1
|
|
|
+ packages statically, therefore this explanation isn't required -->
|
|
|
+
|
|
|
+ <!--<sect2>
|
|
|
+ <title>Notes on Static Linking</title>
|
|
|
+
|
|
|
+ <para>Besides their specific task, most programs have to perform many
|
|
|
+ common and sometimes trivial operations. These include allocating
|
|
|
+ memory, searching directories, reading and writing files, string
|
|
|
+ handling, pattern matching, arithmetic, and other tasks. Instead of
|
|
|
+ obliging each program to reinvent the wheel, the GNU system provides
|
|
|
+ all these basic functions in ready-made libraries. The major library
|
|
|
+ on any Linux system is Glibc.</para>
|
|
|
+
|
|
|
+ <para>There are two primary ways of linking the functions from a
|
|
|
+ library to a program that uses them—statically or dynamically. When
|
|
|
+ a program is linked statically, the code of the used functions is
|
|
|
+ included in the executable, resulting in a rather bulky program. When
|
|
|
+ a program is dynamically linked, it includes a reference to the
|
|
|
+ dynamic linker, the name of the library, and the name of the function,
|
|
|
+ resulting in a much smaller executable. A third option is to use the
|
|
|
+ programming interface of the dynamic linker (see <filename>dlopen(3)</filename>
|
|
|
+ for more information).</para>
|
|
|
+
|
|
|
+ <para>Dynamic linking is the default on Linux and has three major
|
|
|
+ advantages over static linking. First, only one copy of the executable
|
|
|
+ library code is needed on the hard disk, instead of having multiple
|
|
|
+ copies of the same code included in several programs, thus saving
|
|
|
+ disk space. Second, when several programs use the same library
|
|
|
+ function at the same time, only one copy of the function's code is
|
|
|
+ required in core, thus saving memory space. Third, when a library
|
|
|
+ function gets a bug fixed or is otherwise improved, only the one
|
|
|
+ library needs to be recompiled instead of recompiling all programs
|
|
|
+ that make use of the improved function.</para>
|
|
|
+
|
|
|
+ <para>If dynamic linking has several advantages, why then do we
|
|
|
+ statically link the first two packages in this chapter? The reasons
|
|
|
+ are threefold—historical, educational, and technical. The
|
|
|
+ historical reason is that earlier versions of LFS statically linked
|
|
|
+ every program in this chapter. Educationally, knowing the difference
|
|
|
+ between static and dynamic linking is useful. The technical benefit is
|
|
|
+ a gained element of independence from the host, meaning that those
|
|
|
+ programs can be used independently of the host system. However, it is
|
|
|
+ worth noting that an overall successful LFS build can still be
|
|
|
+ achieved when the first two packages are built dynamically.</para>
|
|
|
+
|
|
|
+ </sect2>-->
|
|
|
|
|
|
</sect1>
|
|
|
-
|
Manuel Canales Esparcia