diff options
author | Pierre Labastie <pieere@linuxfromscratch.org> | 2020-06-17 20:50:25 +0000 |
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committer | Pierre Labastie <pieere@linuxfromscratch.org> | 2020-06-17 20:50:25 +0000 |
commit | 12fff1eb8d1c5dcf9c4049d0d08f315d1103787a (patch) | |
tree | a43e983a2e8b0e6b26e28b229b8dab744012a7ec /chapter05 | |
parent | 450e8ac1abb969245e9889493fb09405a55f337c (diff) |
Slightly change the layout in part III, so that the preliminary material
appear separated. Minor rewrites for accounting for the new layout
git-svn-id: http://svn.linuxfromscratch.org/LFS/trunk/BOOK@11949 4aa44e1e-78dd-0310-a6d2-fbcd4c07a689
Diffstat (limited to 'chapter05')
-rw-r--r-- | chapter05/binutils-pass1.xml | 5 | ||||
-rw-r--r-- | chapter05/chapter05.xml | 2 | ||||
-rw-r--r-- | chapter05/generalinstructions.xml | 120 | ||||
-rw-r--r-- | chapter05/introduction.xml | 3 | ||||
-rw-r--r-- | chapter05/toolchaintechnotes.xml | 337 |
5 files changed, 4 insertions, 463 deletions
diff --git a/chapter05/binutils-pass1.xml b/chapter05/binutils-pass1.xml index 914e119b8..09a3a8afd 100644 --- a/chapter05/binutils-pass1.xml +++ b/chapter05/binutils-pass1.xml @@ -43,8 +43,9 @@ <sect2 role="installation"> <title>Installation of Cross Binutils</title> - <note><para>Go back and re-read the notes in the previous section. - Understanding the notes labeled important will save you a lot + <note><para>Go back and re-read the notes in the section titled <xref + linkend="ch-tools-generalinstructions"/>. + Understanding the notes labeled important can save you a lot of problems later.</para></note> <para>It is important that Binutils be the first package compiled diff --git a/chapter05/chapter05.xml b/chapter05/chapter05.xml index 1a2393b93..467a02a36 100644 --- a/chapter05/chapter05.xml +++ b/chapter05/chapter05.xml @@ -12,8 +12,6 @@ <title>Compiling a Cross-Toolchain</title> <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="introduction.xml"/> - <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="toolchaintechnotes.xml"/> - <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="generalinstructions.xml"/> <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="binutils-pass1.xml"/> <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="gcc-pass1.xml"/> <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="linux-headers.xml"/> diff --git a/chapter05/generalinstructions.xml b/chapter05/generalinstructions.xml deleted file mode 100644 index b0a5377e1..000000000 --- a/chapter05/generalinstructions.xml +++ /dev/null @@ -1,120 +0,0 @@ -<?xml version="1.0" encoding="ISO-8859-1"?> -<!DOCTYPE sect1 PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" - "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [ - <!ENTITY % general-entities SYSTEM "../general.ent"> - %general-entities; -]> - -<sect1 id="ch-tools-generalinstructions"> - <?dbhtml filename="generalinstructions.html"?> - - <title>General Compilation Instructions</title> - - <para>When building packages there are several assumptions made within - the instructions:</para> - - <itemizedlist> - - <listitem> - <para>Several of the packages are patched before compilation, but only when - the patch is needed to circumvent a problem. A patch is often needed in - both this and the following chapters, but sometimes in only one location. - Therefore, do not be concerned if instructions for a downloaded patch seem - to be missing. Warning messages about <emphasis>offset</emphasis> or - <emphasis>fuzz</emphasis> may also be encountered when applying a patch. Do - not worry about these warnings, as the patch was still successfully - applied.</para> - </listitem> - - <listitem> - <para>During the compilation of most packages, there will be several - warnings that scroll by on the screen. These are normal and can safely be - ignored. These warnings are as they appear—warnings about - deprecated, but not invalid, use of the C or C++ syntax. C standards change - fairly often, and some packages still use the older standard. This is not a - problem, but does prompt the warning.</para> - </listitem> - - <listitem> - <para>Check one last time that the <envar>LFS</envar> environment variable - is set up properly:</para> - -<screen role="nodump"><userinput>echo $LFS</userinput></screen> - - <para>Make sure the output shows the path to the LFS partition's mount - point, which is <filename class="directory">/mnt/lfs</filename>, using our - example.</para> - </listitem> - - <listitem> - - <para>Finally, two important items must be emphasized:</para> - - <important> - - <para>The build instructions assume that the <xref - linkend='ch-partitioning-hostreqs'/>, including symbolic links, have - been set properly:</para> - - <itemizedlist role='important'> - - <listitem override='bullet'><para><command>bash</command> is the shell - in use.</para></listitem> - - <listitem override='bullet'><para><command>sh</command> is a symbolic - link to <command>bash</command>.</para></listitem> - - <listitem override='bullet'><para><command>/usr/bin/awk</command> is a - symbolic link to <command>gawk</command>.</para></listitem> - - <listitem override='bullet'><para><command>/usr/bin/yacc</command> is a - symbolic link to <command>bison</command> or a small script that - executes bison.</para></listitem> - - </itemizedlist> - </important> - - <important> - <para>To re-emphasize the build process:</para> - - <orderedlist numeration="arabic" spacing="compact"> - <listitem> - <para>Place all the sources and patches in a directory that will be - accessible from the chroot environment such as - <filename class="directory">/mnt/lfs/sources/</filename>.<!-- Do - <emphasis>not</emphasis> put sources in - <filename class="directory">/mnt/lfs/tools/</filename>. --></para> - </listitem> - <listitem> - <para>Change to the sources directory.</para> - </listitem> - <listitem id='buildinstr' xreflabel='Package build instructions'> - <para>For each package:</para> - <orderedlist numeration="loweralpha" spacing="compact"> - <listitem> - <para>Using the <command>tar</command> program, extract the package - to be built. In Chapters 5 and 6, ensure you are - the <emphasis>lfs</emphasis> user when extracting the package.</para> - </listitem> - <listitem> - <para>Change to the directory created when the package was - extracted.</para> - </listitem> - <listitem> - <para>Follow the book's instructions for building the package.</para> - </listitem> - <listitem> - <para>Change back to the sources directory.</para> - </listitem> - <listitem> - <para>Delete the extracted source directory unless instructed otherwise.</para> - </listitem> - </orderedlist> - </listitem> - </orderedlist> - </important> - </listitem> - - </itemizedlist> - -</sect1> diff --git a/chapter05/introduction.xml b/chapter05/introduction.xml index 28b496993..0318acf8b 100644 --- a/chapter05/introduction.xml +++ b/chapter05/introduction.xml @@ -12,8 +12,7 @@ <para>This chapter shows how to build a cross-compiler and its associated tools. Although here cross-compilation is faked, the principles are - the same as for a real cross-toolchain, and are detailed in the next - section.</para> + the same as for a real cross-toolchain.</para> <para>The programs compiled in this chapter will be installed under the <filename class="directory">$LFS/tools</filename> directory to keep them diff --git a/chapter05/toolchaintechnotes.xml b/chapter05/toolchaintechnotes.xml deleted file mode 100644 index 1e7086aaf..000000000 --- a/chapter05/toolchaintechnotes.xml +++ /dev/null @@ -1,337 +0,0 @@ -<?xml version="1.0" encoding="ISO-8859-1"?> -<!DOCTYPE sect1 PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" - "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [ - <!ENTITY % general-entities SYSTEM "../general.ent"> - %general-entities; -]> - -<sect1 id="ch-tools-toolchaintechnotes"> - <?dbhtml filename="toolchaintechnotes.html"?> - - <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 - to at any time during the process.</para> - - <para>The overall goal of this chapter and <xref - linkend="chapter-temporary-tools"/> is to produce a temporary area that - contains a known-good set of tools that can be isolated from the host system. - By using <command>chroot</command>, the commands in the remaining chapters - will be contained within that environment, ensuring a clean, trouble-free - build of the target LFS system. The build process has been designed to - minimize the risks for new readers and to provide the most educational value - at the same time.</para> - - <para>The build process is based on the process of - <emphasis>cross-compilation</emphasis>. Cross-compilation is normally used - for building a compiler and its toolchain for a machine different from - the one that is used for the build. This is not strictly needed for LFS, - since the machine where the new system will run is the same as the one - used for the build. But cross-compilation has the great advantage that - anything that is cross-compiled cannot depend on the host environment.</para> - - <sect2 id="cross-compile" xreflabel="About Cross-Compilation"> - - <title>About Cross-Compilation</title> - - <para>Cross-compilation involves some concepts that deserve a section on - their own. Although this section may be omitted in a first reading, it - is strongly suggested to come back to it later in order to get a full - grasp of the build process.</para> - - <para>Let us first define some terms used in this context:</para> - - <variablelist> - <varlistentry><term>build</term><listitem> - <para>is the machine where we build programs. Note that this machine - is referred to as the <quote>host</quote> in other - sections.</para></listitem> - </varlistentry> - - <varlistentry><term>host</term><listitem> - <para>is the machine/system where the built programs will run. Note - that this use of <quote>host</quote> is not the same as in other - sections.</para></listitem> - </varlistentry> - - <varlistentry><term>target</term><listitem> - <para>is only used for compilers. It is the machine the compiler - produces code for. It may be different from both build and - host.</para></listitem> - </varlistentry> - - </variablelist> - - <para>As an example, let us imagine the following scenario: we may have a - compiler on a slow machine only, let's call the machine A, and the compiler - ccA. We may have also a fast machine (B), but with no compiler, and we may - want to produce code for a another slow machine (C). Then, to build a - compiler for machine C, we would have three stages:</para> - - <informaltable align="center"> - <tgroup cols="5"> - <colspec colnum="1" align="center"/> - <colspec colnum="2" align="center"/> - <colspec colnum="3" align="center"/> - <colspec colnum="4" align="center"/> - <colspec colnum="5" align="left"/> - <thead> - <row><entry>Stage</entry><entry>Build</entry><entry>Host</entry> - <entry>Target</entry><entry>Action</entry></row> - </thead> - <tbody> - <row> - <entry>1</entry><entry>A</entry><entry>A</entry><entry>B</entry> - <entry>build cross-compiler cc1 using ccA on machine A</entry> - </row> - <row> - <entry>2</entry><entry>A</entry><entry>B</entry><entry>B</entry> - <entry>build cross-compiler cc2 using cc1 on machine A</entry> - </row> - <row> - <entry>3</entry><entry>B</entry><entry>C</entry><entry>C</entry> - <entry>build compiler ccC using cc2 on machine B</entry> - </row> - </tbody> - </tgroup> - </informaltable> - - <para>Then, all the other programs needed by machine C can be compiled - using cc2 on the fast machine B. Note that unless B can run programs - produced for C, there is no way to test the built programs until machine - C itself is running. For example, for testing ccC, we may want to add a - fourth stage:</para> - - <informaltable align="center"> - <tgroup cols="5"> - <colspec colnum="1" align="center"/> - <colspec colnum="2" align="center"/> - <colspec colnum="3" align="center"/> - <colspec colnum="4" align="center"/> - <colspec colnum="5" align="left"/> - <thead> - <row><entry>Stage</entry><entry>Build</entry><entry>Host</entry> - <entry>Target</entry><entry>Action</entry></row> - </thead> - <tbody> - <row> - <entry>4</entry><entry>C</entry><entry>C</entry><entry>C</entry> - <entry>rebuild and test ccC using itself on machine C</entry> - </row> - </tbody> - </tgroup> - </informaltable> - - <para>In the example above, only cc1 and cc2 are cross-compilers, that is, - they produce code for a machine different from the one they are run on. - The other compilers ccA and ccC produce code for the machine they are run - on. Such compilers are called <emphasis>native</emphasis> compilers.</para> - - </sect2> - - <sect2 id="lfs-cross"> - <title>Implementation of Cross-Compilation for LFS</title> - - <note> - <para>Almost all the build systems use names of the form - cpu-vendor-kernel-os referred to as the machine triplet. An astute - reader may wonder why a <quote>triplet</quote> refers to a four component - name. The reason is history: initially, three component names were enough - to designate unambiguously a machine, but with new machines and systems - appearing, that proved insufficient. The word <quote>triplet</quote> - remained. A simple way to determine your machine 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. For example, for a 32-bit Intel processor the - output will be <emphasis>i686-pc-linux-gnu</emphasis>. On a 64-bit - system it will be <emphasis>x86_64-pc-linux-gnu</emphasis>.</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 for a 32-bit Intel machine will be <filename - class="libraryfile">ld-linux.so.2</filename> (<filename - class="libraryfile">ld-linux-x86-64.so.2</filename> for 64-bit systems). A - sure-fire way to determine the name of the dynamic linker 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> - </note> - - <para>In order to fake a cross compilation, the name of the host triplet - is slightly adjusted by changing the "vendor" field in the - <envar>LFS_TGT</envar> variable. We also use the - <parameter>--with-sysroot</parameter> option when building the cross linker and - cross compiler to tell them where to find the needed host files. This - ensures that none of the other programs built in <xref - linkend="chapter-temporary-tools"/> can link to libraries on the build - machine. Only two stages are mandatory, and one more for tests:</para> - - <informaltable align="center"> - <tgroup cols="5"> - <colspec colnum="1" align="center"/> - <colspec colnum="2" align="center"/> - <colspec colnum="3" align="center"/> - <colspec colnum="4" align="center"/> - <colspec colnum="5" align="left"/> - <thead> - <row><entry>Stage</entry><entry>Build</entry><entry>Host</entry> - <entry>Target</entry><entry>Action</entry></row> - </thead> - <tbody> - <row> - <entry>1</entry><entry>pc</entry><entry>pc</entry><entry>lfs</entry> - <entry>build cross-compiler cc1 using cc-pc on pc</entry> - </row> - <row> - <entry>2</entry><entry>pc</entry><entry>lfs</entry><entry>lfs</entry> - <entry>build compiler cc-lfs using cc1 on pc</entry> - </row> - <row> - <entry>3</entry><entry>lfs</entry><entry>lfs</entry><entry>lfs</entry> - <entry>rebuild and test cc-lfs using itself on lfs</entry> - </row> - </tbody> - </tgroup> - </informaltable> - - <para>In the above table, <quote>on pc</quote> means the commands are run - on a machine using the already installed distribution. <quote>On - lfs</quote> means the commands are run in a chrooted environment.</para> - - <para>Now, there is more about cross-compiling: the C language is not - just a compiler, but also defines a standard library. In this book, the - GNU C library, named glibc, is used. This library must - be compiled for the lfs machine, that is, using the cross compiler cc1. - But the compiler itself uses an internal library implementing complex - instructions not available in the assembler instruction set. This - internal library is named libgcc, and must be linked to the glibc - library to be fully functional! Furthermore, the standard library for - C++ (libstdc++) also needs being linked to glibc. The solution - to this chicken and egg problem is to first build a degraded cc1 based libgcc, - lacking some fuctionalities such as threads and exception handling, then - build glibc using this degraded compiler (glibc itself is not - degraded), then build libstdc++. But this last library will lack the - same functionalities as libgcc.</para> - - <para>This is not the end of the story: the conclusion of the preceding - paragraph is that cc1 is unable to build a fully functional libstdc++, but - this is the only compiler available for building the C/C++ libraries - during stage 2! Of course, the compiler built during stage 2, cc-lfs, - would be able to build those libraries, but (1) the build system of - GCC does not know that it is usable on pc, and (2) using it on pc - would be at risk of linking to the pc libraries, since cc-lfs is a native - compiler. So we have to build libstdc++ later, in chroot.</para> - - </sect2> - - <sect2 id="other-details"> - - <title>Other procedural details</title> - - <para>The cross-compiler will be installed in a separate <filename - class="directory">$LFS/tools</filename> directory, since it will not - be part of the final system.</para> - - <para>Binutils is installed first because the <command>configure</command> - runs of both GCC and Glibc perform various feature tests on the assembler - and linker to determine which software features to enable or disable. This - is more important than one might first realize. An incorrectly configured - GCC or Glibc can result in a subtly broken toolchain, where the impact of - such breakage might not show up until near the end of the build of an - entire distribution. A test suite failure will usually highlight this error - before too much additional work is performed.</para> - - <para>Binutils installs its assembler and linker in two locations, - <filename class="directory">$LFS/tools/bin</filename> and <filename - class="directory">$LFS/tools/$LFS_TGT/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, <command>$LFS_TGT-ld --verbose | grep SEARCH</command> - will illustrate the current search paths and their order. It shows which - files are linked by <command>ld</command> by compiling a dummy program and - passing the <parameter>--verbose</parameter> switch to the linker. For - example, - <command>$LFS_TGT-gcc dummy.c -Wl,--verbose 2>&1 | grep succeeded</command> - 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... /mnt/lfs/tools/i686-lfs-linux-gnu/bin/as -checking what linker to use... /mnt/lfs/tools/i686-lfs-linux-gnu/bin/ld</computeroutput></screen> - - <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: <command>$LFS_TGT-gcc -print-prog-name=ld</command>.</para> - - <para>Detailed information can be obtained from <command>gcc</command> by - passing it the <parameter>-v</parameter> command line option while compiling - a dummy program. For example, <command>gcc -v dummy.c</command> will show - detailed information about the preprocessor, compilation, and assembly - stages, including <command>gcc</command>'s included search paths and their - order.</para> - - <para>Next installed are sanitized Linux API headers. These allow the - standard C library (Glibc) to interface with features that the Linux - kernel will provide.</para> - - <para>The next package installed is Glibc. The most important - considerations for building Glibc are the compiler, binary tools, and - kernel headers. The compiler is generally not an issue since Glibc will - always use the compiler relating to the <parameter>--host</parameter> - parameter passed to its configure script; e.g. in our case, the compiler - will be <command>$LFS_TGT-gcc</command>. 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">build</filename> directory for all important details. - Note the use of <parameter>CC="$LFS_TGT-gcc"</parameter> (with - <envar>$LFS_TGT</envar> expanded) 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>As said above, the standard C++ library is compiled next, followed in - Chapter 6 by all the programs that need themselves to be built. The install - step of libstdc++ uses the <envar>DESTDIR</envar> variable to have the - programs land into the LFS filesystem.</para> - - <para>In Chapter 7 the native lfs compiler is built. First binutils-pass2, - with the same <envar>DESTDIR</envar> install as the other programs is - built, and then the second pass of GCC is constructed, omitting libstdc++ - and other non-important libraries. Due to some weird logic in GCC's - configure script, <envar>CC_FOR_TARGET</envar> ends up as - <command>cc</command> when the host is the same as the target, but is - different from the build system. This is why - <parameter>CC_FOR_TARGET=$LFS_TGT-gcc</parameter> is put explicitely into - the configure options.</para> - - <para>Upon entering the chroot environment in <xref - linkend="chapter-chroot-temporary-tools"/>, the first task is to install - libstdc++. Then temporary installations of programs needed for the proper - operation of the toolchain are performed. Programs needed for testing - other programs are also built. From this point onwards, the - core toolchain is self-contained and self-hosted. In - <xref linkend="chapter-building-system"/>, final versions of all the - packages needed for a fully functional system are built, tested and - installed.</para> - - </sect2> - -</sect1> |