doc/oops-tracing: add Code: decode info

Add info that the Code: bytes line contains <xy> or (wxyz) in some
architecture oops reports and what that means.

Add a script by Andi Kleen that reads the Code: line from an Oops report
file and generates assembly code from the hex bytes.
Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Cc: Andi Kleen <ak@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Documentation/oops-tracing.txt

@@ -86,6 +86,20 @@ stuff are the values reported by the Oops - you can just cut-and-paste
 and do a replace of spaces to "\x" - that's what I do, as I'm too lazy 
 to write a program to automate this all).
 
+Alternatively, you can use the shell script in scripts/decodecode.
+Its usage is:  decodecode < oops.txt
+
+The hex bytes that follow "Code:" may (in some architectures) have a series
+of bytes that precede the current instruction pointer as well as bytes at and
+following the current instruction pointer.  In some cases, one instruction
+byte or word is surrounded by <> or (), as in "<86>" or "(f00d)".  These
+<> or () markings indicate the current instruction pointer.  Example from
+i386, split into multiple lines for readability:
+
+Code: f9 0f 8d f9 00 00 00 8d 42 0c e8 dd 26 11 c7 a1 60 ea 2b f9 8b 50 08 a1
+64 ea 2b f9 8d 34 82 8b 1e 85 db 74 6d 8b 15 60 ea 2b f9 <8b> 43 04 39 42 54
+7e 04 40 89 42 54 8b 43 04 3b 05 00 f6 52 c0
+
 Finally, if you want to see where the code comes from, you can do
 
 	cd /usr/src/linux

scripts/decodecode

+#!/bin/sh
+# Disassemble the Code: line in Linux oopses
+# usage: decodecode < oops.file
+#
+# options: set env. variable AFLAGS=options to pass options to "as";
+# e.g., to decode an i386 oops on an x86_64 system, use:
+# AFLAGS=--32 decodecode < 386.oops
+
+T=`mktemp`
+code=
+
+while read i ; do
+
+case "$i" in
+*Code:*)
+	code=$i
+	;;
+esac
+
+done
+
+if [ -z "$code" ]; then
+	exit
+fi
+
+echo $code
+code=`echo $code | sed -e 's/.*Code: //'`
+
+marker=`expr index "$code" "\<"`
+if [ $marker -eq 0 ]; then
+	marker=`expr index "$code" "\("`
+fi
+
+if [ $marker -ne 0 ]; then
+	beforemark=`echo "$code" | cut -c-$((${marker} - 1))`
+	echo -n "	.byte 0x" > $T.s
+	echo $beforemark | sed -e 's/ /,0x/g' >> $T.s
+	as $AFLAGS -o $T.o $T.s
+	objdump -S $T.o
+	rm $T.o $T.s
+
+# and fix code at-and-after marker
+	code=`echo "$code" | cut -c$((${marker} + 1))-`
+fi
+
+code=`echo $code | sed -e 's/ [<(]/ /;s/[>)] / /;s/ /,0x/g'`
+echo -n "	.byte 0x" > $T.s
+echo $code >> $T.s
+as $AFLAGS -o $T.o $T.s
+objdump -S $T.o
+rm $T.o $T.s