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diff --git a/rts/gmp/mpn/x86/k6/cross.pl b/rts/gmp/mpn/x86/k6/cross.pl
new file mode 100644
index 0000000..21734f3
--- /dev/null
+++ b/rts/gmp/mpn/x86/k6/cross.pl
@@ -0,0 +1,141 @@
+#! /usr/bin/perl
+
+# Copyright (C) 2000 Free Software Foundation, Inc.
+#
+# This file is part of the GNU MP Library.
+#
+# The GNU MP Library is free software; you can redistribute it and/or modify
+# it under the terms of the GNU Lesser General Public License as published
+# by the Free Software Foundation; either version 2.1 of the License, or (at
+# your option) any later version.
+#
+# The GNU MP Library is distributed in the hope that it will be useful, but
+# WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+# or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
+# License for more details.
+#
+# You should have received a copy of the GNU Lesser General Public License
+# along with the GNU MP Library; see the file COPYING.LIB.  If not, write to
+# the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
+# MA 02111-1307, USA.
+
+
+# Usage: cross.pl [filename.o]...
+#
+# Produce an annotated disassembly of the given object files, indicating
+# certain code alignment and addressing mode problems afflicting K6 chips.
+# "ZZ" is used on all annotations, so this can be searched for.
+#
+# With no arguments, all .o files corresponding to .asm files are processed.
+# This is good in the mpn object directory of a k6*-*-* build.
+#
+# As far as fixing problems goes, any cache line crossing problems in loops
+# get attention, but as a rule it's too tedious to rearrange code or slip in
+# nops to fix every problem in setup or finishup code.
+#
+# Bugs:
+#
+# Instructions without mod/rm bytes or which are already vector decoded are
+# unaffected by cache line boundary crossing, but not all of these have yet
+# been put in as exceptions.  All that occur in practice in GMP are present
+# though.
+#
+# There's no messages for using the vector decoded addressing mode (%esi),
+# but that mode is easy to avoid when coding.
+
+use strict;
+
+sub disassemble {
+    my ($file) = @_;
+    my ($addr,$b1,$b2,$b3, $prefix,$opcode,$modrm);
+
+    open (IN, "objdump -Srfh $file |")
+	|| die "Cannot open pipe from objdump\n";
+    while (<IN>) {
+	print;
+
+	if (/^[ \t]*[0-9]+[ \t]+\.text[ \t]/ && /2\*\*([0-9]+)$/) {
+	    if ($1 < 5) {
+		print "ZZ need at least 2**5 for predictable cache line crossing\n";
+	    }
+	}
+	
+	if (/^[ \t]*([0-9a-f]*):[ \t]*([0-9a-f]+)[ \t]+([0-9a-f]+)[ \t]+([0-9a-f]+)/) {
+	    ($addr,$b1,$b2,$b3) = ($1,$2,$3,$4);
+
+	} elsif (/^[ \t]*([0-9a-f]*):[ \t]*([0-9a-f]+)[ \t]+([0-9a-f]+)/) {
+	    ($addr,$b1,$b2,$b3) = ($1,$2,$3,'');
+
+	} elsif (/^[ \t]*([0-9a-f]*):[ \t]*([0-9a-f]+)/) {
+	    ($addr,$b1,$b2,$b3) = ($1,$2,'','');
+
+	} else {
+	    next;
+	}
+
+	if ($b1 =~ /0f/) {
+	    $prefix = $b1;
+	    $opcode = $b2;
+	    $modrm = $b3;
+	} else {
+	    $prefix = '';
+	    $opcode = $b1;
+	    $modrm = $b2;
+	}
+
+	# modrm of the form 00-xxx-100 with an 0F prefix is the problem case
+	# for K6 and pre-CXT K6-2
+	if ($prefix =~ /0f/
+	    && $opcode !~ /^8/         # jcond disp32
+	    && $modrm =~ /^[0-3][4c]/) {
+	    print "ZZ ($file) >3 bytes to determine instruction length\n";
+	}
+
+	# with just an opcode, starting 1f mod 20h
+	if ($addr =~ /[13579bdf]f$/
+	    && $prefix !~ /0f/
+	    && $opcode !~ /1[012345]/ # adc
+	    && $opcode !~ /1[89abcd]/ # sbb
+	    && $opcode !~ /68/        # push $imm32
+	    && $opcode !~ /^7/        # jcond disp8
+	    && $opcode !~ /a[89]/     # test+imm
+	    && $opcode !~ /a[a-f]/    # stos/lods/scas
+	    && $opcode !~ /b8/        # movl $imm32,%eax
+	    && $opcode !~ /e[0123]/   # loop/loopz/loopnz/jcxz
+	    && $opcode !~ /e[b9]/     # jmp disp8/disp32
+	    && $opcode !~ /f[89abcd]/ # clc,stc,cli,sti,cld,std
+	    && !($opcode =~ /f[67]/          # grp 1
+		 && $modrm =~ /^[2367abef]/) # mul, imul, div, idiv
+	    && $modrm !~ /^$/) {
+	    print "ZZ ($file) opcode/modrm cross 32-byte boundary\n";
+	}
+
+	# with an 0F prefix, anything starting at 1f mod 20h
+	if ($addr =~ /[13579bdf][f]$/
+	    && $prefix =~ /0f/) {
+	    print "ZZ ($file) prefix/opcode cross 32-byte boundary\n";
+	}
+
+	# with an 0F prefix, anything with mod/rm starting at 1e mod 20h
+	if ($addr =~ /[13579bdf][e]$/
+	    && $prefix =~ /0f/
+	     && $opcode !~ /^8/        # jcond disp32
+	    && $modrm !~ /^$/) {
+	    print "ZZ ($file) prefix/opcode/modrm cross 32-byte boundary\n";
+	}
+    }
+    close IN || die "Error from objdump (or objdump not available)\n";
+}
+
+
+my @files;
+if ($#ARGV >= 0) {
+    @files = @ARGV;
+} else {
+    @files = glob "*.asm";
+    map {s/.asm/.o/} @files;
+}
+
+foreach (@files)  {
+    disassemble($_);
+}