[Bug 233863] Various PowerMac G5 models may require kern.smp.disabled=1 and must set usefdt=1 which causes net interface reorder

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=233863

--- Comment #39 from Mark Millard <marklmi26-fbsd at yahoo.com> ---
(In reply to Mark Millard from comment #38)

I forgot to warn that head -r347463 without any patching
has world messed up for older powerpc64 processors like
the 970 family: it is using the newer instruction cmpb in
its strcmp implementation in libc.

I dealt with this issue with a patch that avoids cmpb:
(not appropriate or required for head -r345758 were
the previouosly-attached patches are targeted)

# svnlite diff /mnt/usr/src/
Index: /mnt/usr/src/lib/libc/powerpc64/string/strcmp.S
===================================================================
--- /mnt/usr/src/lib/libc/powerpc64/string/strcmp.S     (revision 347463)
+++ /mnt/usr/src/lib/libc/powerpc64/string/strcmp.S     (working copy)
@@ -88,9 +88,16 @@
.Lstrcmp_compare_by_word:
        ld      %r5,0(%r3)      /* Load double words. */
        ld      %r6,0(%r4)
-       xor     %r8,%r8,%r8     /* %r8 <- Zero. */
+       lis     %r8,32639       /* 0x7f7f */
+       ori     %r8,%r8,32639   /* 0x7f7f7f7f */
+       rldimi  %r8,%r8,32,0    /* 0x7f7f7f7f'7f7f7f7f */
        xor     %r0,%r5,%r6     /* Check if double words are different. */
-       cmpb    %r7,%r5,%r8     /* Check if double words contain zero. */
+                               /* Check for zero vs. not bytes: */
+       and     %r9,%r5,%r8     /* 0x00->0x00, 0x80->0x00,
other->ms-bit-in-byte==0 */
+       add     %r9,%r9,%r8     /*     ->0x7f,     ->0x7f,     
->ms-bit-in-byte==1 */
+       nor     %r7,%r9,%r5     /*     ->0x80,     ->0x00,     
->ms-bit-in-byte==0 */
+       andc    %r7,%r7,%r8     /*     ->0x80,     ->0x00,      ->0x00 */
+                               /* sort of like cmpb %r7,%r5,%r8 for %r8 being
zero */

        /*
         * If double words are different or contain zero,
@@ -104,7 +111,12 @@
        ldu     %r5,8(%r3)      /* Load double words. */
        ldu     %r6,8(%r4)
        xor     %r0,%r5,%r6     /* Check if double words are different. */
-       cmpb    %r7,%r5,%r8     /* Check if double words contain zero. */
+                               /* Check for zero vs. not bytes: */
+       and     %r9,%r5,%r8     /* 0x00->0x00, 0x80->0x00,
other->ms-bit-in-byte==0 */
+       add     %r9,%r9,%r8     /*     ->0x7f,     ->0x7f,     
->ms-bit-in-byte==1 */
+       nor     %r7,%r9,%r5     /*     ->0x80,     ->0x00,     
->ms-bit-in-byte==0 */
+       andc    %r7,%r7,%r8     /*     ->0x80,     ->0x00,      ->0x00 */
+                               /* sort of like cmpb %r7,%r5,%r8 for %r8 being
zero */

        /*
         * If double words are different or contain zero,

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