lfs-book-zh_CN/chapter05/gcc-inst.xml

<sect2><title>&nbsp;</title><para>&nbsp;</para></sect2>

<sect2>
<title>Installation of GCC</title>

<para>We won't be needing a C++ compiler until Chapter 6. So, only
the gcc-core tarball needs to be unpacked at this time.</para>

<para>This package is known to behave badly when you have changed its
default optimization flags (including the -march and -mcpu options).
Therefore, if you have defined any environment variables that override
default optimizations, such as CFLAGS and CXXFLAGS, we recommend unsetting
or modifying them when building GCC.</para>

<para>It is recommended by the GCC installation documentation to build
GCC outside of the source directory in a dedicated directory:</para>

<para><screen><userinput>mkdir ../gcc-build
cd ../gcc-build</userinput></screen></para>

<para>Prepare GCC to be compiled:</para>

<para><screen><userinput>../gcc-&gcc-version;/configure --prefix=/static \
&nbsp;&nbsp;&nbsp;--disable-nls --disable-shared \
&nbsp;&nbsp;&nbsp;--with-as=$LFS/static/bin/as \
&nbsp;&nbsp;&nbsp;--with-ld=$LFS/static/bin/ld</userinput></screen></para>

<para>The meaning of the configure options are:</para>

<itemizedlist>
<listitem><para><userinput>--prefix=/static</userinput>: This is NOT a
typo. GCC hard codes some paths while compiling and so we need to pass
<filename class="directory">/static</filename> as the prefix during the
configure stage. We will pass the real installation prefix (<filename
class="directory">$LFS/static</filename>) during the installation
stage later on.</para></listitem>

<listitem><para><userinput>--disable-shared</userinput>: This prevents the
build of dynamic libraries. They are useless to us at the moment. We'll
create them when we reinstall GCC in chapter 6.</para></listitem>

<listitem><para><userinput>--with-as=$LFS/static/bin/as and
--with-ld=$LFS/static/bin/ld</userinput>: GCC can be miscompiled if your
host distribution's Binutils package is quite old. We need a good working
static GCC until we reinstall GCC later in chapter 6. So by using
<filename>as</filename> and <filename>ld</filename> from the Binutils
package we compiled earlier in this chapter we ensure that GCC will work
correctly.</para></listitem>
</itemizedlist>

<para>Continue with compiling the package:</para>

<para><screen><userinput>make BOOT_LDFLAGS="-static" bootstrap</userinput></screen></para>

<para>The meaning of the make options are:</para>

<itemizedlist>
<listitem><para><userinput>BOOT_LDFLAGS="-static"</userinput>: This is
GCC's equivalent to make LDFLAGS="-static" as we use with other packages to
compile them statically.</para></listitem>

<listitem><para><userinput>bootstrap</userinput>: The
<emphasis>bootstrap</emphasis> target doesn't just compile GCC, but it
compiles GCC a second time. It uses the first compiled programs to compile
itself a second and third time to make sure the compiler was compiled properly
and can compile itself properly.</para></listitem>
</itemizedlist>

<para>And finish off installing the package:</para>

<para><screen><userinput>make prefix=$LFS/static install-no-fixedincludes</userinput></screen></para>

<para>The meaning of the make option is:</para>

<itemizedlist>
<listitem><para><userinput>install-no-fixedincludes</userinput>: This prevents
the fixincludes script from running. Preventing this is necessary because
under normal circumstances the GCC installation will run the fixincludes
script which scans your system for header files that need to be fixed. It
might find that the Glibc header files of your host system need to be fixed.
If so, it will fix them and put them in
<filename>$LFS/static/lib/gcc-lib/i686-pc-linux-gnu/3.2</filename>. Later on
in chapter 6 you will install Glibc which will put its header files in
<filename>/usr/include</filename>. Next you will install other programs that
use the Glibc headers and GCC will look in
<filename>/static/lib/gcc-lib</filename> before looking in
<filename>/usr/include</filename>, with the result of finding and using the
fixed Glibc header files from your host distribution, which are probably
incompatible with the Glibc version actually used on the LFS
system.</para></listitem>
</itemizedlist>

<para>As the finishing touch we'll create the <filename
class="symlink">$LFS/static/bin/cc</filename> symlink. A lot of programs
and scripts try to run <userinput>cc</userinput> instead of
<userinput>gcc</userinput> This is to keep programs generic and usable on
all kinds of Unix systems. Not everybody has GNU CC installed. Just running
<userinput>cc</userinput> (C Compiler) leaves the user free to decide which
C compiler to install. The symlink will point to the system's default
compiler.</para>

<para><screen><userinput>ln -s gcc $LFS/static/bin/cc</userinput></screen></para>

</sect2>