Changeset 2469049 for chapter05/gcc-pass1.xml

Timestamp:

02/28/2024 04:02:53 PM (7 months ago)

Author:

Xi Ruoyao <xry111@…>

Branches:

xry111/mips64el

Children:

9d92ca9

Parents:

959783e

git-author:

Xi Ruoyao <xry111@…> (01/03/2024 09:14:59 AM)

git-committer:

Xi Ruoyao <xry111@…> (02/28/2024 04:02:53 PM)

Message:

mips64el: gcc: Add --with-nan=2008 if needed

File:

• chapter05/gcc-pass1.xml (modified) (4 diffs)

chapter05/gcc-pass1.xml

@@ -75 +75 @@
 cd       build</userinput></screen>
 
+    <para>Probe the NaN encoding of the CPU:</para>
+
+<screen><userinput remap="pre">cat > nan2008.c &lt;&lt; \EOF
+<literal>#include &lt;stdio.h&gt;
+int main()
+{
+  int x;
+  asm("cfc1\t%0,$31":"=r"(x));
+  return !(x &amp; 1 &lt;&lt; 18);
+}</literal>
+EOF
+gcc nan2008.c -o nan2008
+if ./nan2008; then
+  NAN_SWITCH=--with-nan=2008
+fi</userinput></screen>
+
     <para>Prepare GCC for compilation:</para>
 
@@ -80 +96 @@
     --target=$LFS_TGT         \
     --prefix=$LFS/tools       \
+    --with-arch=mips64r2      \
     --with-glibc-version=&glibc-version; \
     --with-sysroot=$LFS       \
@@ -96 +113 @@
     --disable-libvtv          \
     --disable-libstdcxx       \
-    --enable-languages=c,c++</userinput></screen>
+    --enable-languages=c,c++  \
+    $NAN_SWITCH</userinput></screen>
     <variablelist>
       <title>The meaning of the configure options:</title>
+
+      <varlistentry>
+        <term><parameter>--with-arch=mips64r2</parameter></term>
+        <listitem>
+          <para>Set the default value of <option>-march=</option> to
+          mips64r2.  Most distros use it as the baseline for the MIPS port,
+          so we are doing the same.  You may change it if your CPU is not
+          compatible with mips64r2 (for example, mips3 or mips64r6), or
+          your CPU is stronger than mips64r2 and you don't care about the
+          compatibility with mips64r2, but we've not tested any setting
+          other than mips64r2.</para>
+        </listitem>
+      </varlistentry>
 
       <varlistentry>
@@ -179 +210 @@
           <para>This option ensures that only the C and C++ compilers are built.
           These are the only languages needed now.</para>
+        </listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><parameter>$NAN_SWITCH</parameter></term>
+        <listitem>
+          <para>If the CPU encodes NaN (Not a Number) values following
+          IEEE 754-2008 (indicated by the 16th bit of FCSR), this variable
+          will be set to <option>--with-nan=2008</option> so GCC will be
+          configured to use the IEEE 754-2008 encoding for NaN values as
+                  the default.  If this option is not properly set to match the CPU,
+                  many Glibc and Python tests will fail because of the wrong NaN
+                  encoding.</para>
         </listitem>
       </varlistentry>