Re: [PATCH 6/15] bootwrapper: switch 64 bit cpus to 32 bit mode

+	/* Check if the processor is running in 32 bit mode, using
+	 * only 32 bit instructions which should be safe on 32 and
+	 * 64 bit processors.
+	 *
+	 * Subtract the bottom 32 bits of MSR from the full value
+	 * recording the result.  Since MSR[SF] is in the high word,
+	 * the result will be not-equal iff in 32 bit mode (either
+	 * the processor is a 32 bit processor or MSR[SF] = 0).
+	 */

The other way around -- the processor is 64-bit and MSR[SF]=1.

Great trick btw! :-)

+	mfmsr	r0		/* grab whole msr		*/
+	rlwinm	r8,r0,0,0,31	/* extract bottom word		*/
+	subf.	r8,r8,r0	/* subtract, same?		*/
+	beq	0f		/* yes: we are 32 bit mode	*/

The code is fine though.


Segher