[lfs] 02/02: Merge

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commit 9033e119b98c4b57ca72ef4aec74f5d3e0d26ece
Merge: 30e7d2fd3 6026724d1
Author: Thomas Trepl <[email protected]>
AuthorDate: Sat Aug 16 05:29:06 2025 +0200

    Merge

 chapter05/gcc-pass1.xml | 18 +++++++++++++++++-
 1 file changed, 17 insertions(+), 1 deletion(-)

diff --cc chapter05/gcc-pass1.xml
index d5051f0bd,3a537e014..03eb4d86a
--- a/chapter05/gcc-pass1.xml
+++ b/chapter05/gcc-pass1.xml
@@@ -72,45 -72,23 +72,61 @@@ mv -v mpc-&mpc-version; mpc</userinput>
   ;;
  esac</userinput></screen>
  
+     <note>
+       <para>
+         This example demonstrates the use of the
+         <parameter>-i.orig</parameter> switch.  It makes the
+         <command>sed</command> copy the <filename>t-linux64</filename>
+         to <filename>t-linux64.orig</filename>, and then edit the
+         <filename>t-linux64</filename> inplace.  So you may run
+         <command>diff -u gcc/config/i386/t-linux64{.orig,}</command>
+         to visualize the change done by the <command>sed</command> command
+         afterwards.  We'll simply use <parameter>-i</parameter> (which just
+         edits the original file inplace without copying it) for all other
+         packages in the book, but you can change it to
+         <parameter>-i.orig</parameter> in any case you want to keep a copy
+         of the original file.
+       </para>
+     </note>
+ 
 +    <para arch="ml_32,ml_x32,ml_all">Change the default directory name for
 +    libraries:</para>
 +
 +<screen arch="ml_32,ml_x32,ml_all"><userinput remap="pre">sed -e '/m64=/s/lib64/lib/' \
 +    -e '/m32=/s/m32=.*/m32=..\/lib32$(call if_multiarch,:i386-linux-gnu)/' \
 +    -i.orig gcc/config/i386/t-linux64
 +</userinput></screen>
 +
 +    <para arch="ml_32,ml_all">Make <literal>-mstackrealign</literal>
 +      a default for 32bit objects:</para>
 +
 +<screen arch="ml_32,ml_all"><userinput remap="pre">sed '/STACK_REALIGN_DEFAULT/s/0/(!TARGET_64BIT \&amp;\&amp; TARGET_SSE)/' \
 +      -i gcc/config/i386/i386.h</userinput></screen>
 +
 +    <note arch="ml_32,ml_all">
 +      <para>Adding the <literal>-mstackrealign</literal> flag by default
 +        helps to overcome issues with old binaries which cannot be
 +        recompiled on the actual OS.</para>
 +
 +      <!-- Thanks to xry111 for explaining the technical background: -->
 +
 +      <para>Today the x86-32 SysV psABI (used by all Linux programs)
 +        mandates a 16-byte alignment of the stack frame, so the routines
 +        using SSE will save/load SSE vectors onto/from the stack using a
 +        <literal>movaps</literal> instruction (which only works with
 +        aligned addresses, but faster than its counterpart allowing
 +        unaligned addresses, <literal>movups</literal>).</para>
 +
 +      <para>But some really old x86-32 Linux binaries (compiled about
 +        15 years ago), and all Windows x86-32 binaries which might be
 +        run via <application>Wine</application> or <application>Steam</application>
 +        only aligns the
 +        stack frame to 4-byte. Thus, when it calls a SSE routine in LFS
 +        built without <literal>-mstackrealign</literal>, the
 +        <literal>movdqa</literal> instruction fails with a General
 +        Protection Error and the Linux kernel terminates the process
 +        with a SIGSEGV.</para>
-     </note>
 +
      <para>The GCC documentation recommends building GCC
      in a dedicated build directory:</para>
  

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