Subject: [PATCH] force stackpointer alignment in 64bit kernel

From: Olaf Hering <[email-masked]>
Date: Fri, 3 Mar 2006 20:16:33 +0100

Fix gcc "bug" #26549 which causes pointers to be truncated.

The address of variable val in prom_init_stdout is passed to prom_getprop.
prom_getprop casts the pointer to u32 and passes it to call_prom in the hope
that OpenFirmware stores something there.
But the pointer is truncated in the lower bits and the expected value is
stored somewhere else.

In my testing I had a stackpointer of 0x0023e6b4. val was at offset 120, 
wich has address 0x0023e72c. But the value passed to OF was 0x0023e728.

c00000000040b710:       3b 01 00 78     addi    r24,r1,120
...
c00000000040b754:       57 08 00 38     rlwinm  r8,r24,0,0,28
...
c00000000040b784:       80 01 00 78     lwz     r0,120(r1)
...
c00000000040b798:       90 1b 00 0c     stw     r0,12(r27)
...

The stackpointer came from 32bit code, which appearently has different
alignment rules than 64bit code. The chain was yaboot -> zImage -> vmlinux
Force the stackpointer to be 16 byte aligned.

Signed-off-by: Olaf Hering <[email-masked]>

 arch/powerpc/kernel/head_64.S |    2 ++
 1 files changed, 2 insertions(+)

Index: linux-2.6.16-rc5-olh/arch/powerpc/kernel/head_64.S
===================================================================
--- linux-2.6.16-rc5-olh.orig/arch/powerpc/kernel/head_64.S
+++ linux-2.6.16-rc5-olh/arch/powerpc/kernel/head_64.S
@@ -1547,6 +1547,8 @@ _STATIC(__boot_from_prom)
 	mr	r27,r7
 
 	/* Make sure we are running in 64 bits mode */
+	addi	r1,r1,16
+	rlwinm	r1,r1,0,0,28
 	bl	.enable_64b_mode
 
 	/* put a relocation offset into r3 */