From 6088857b169c64e6e9672a2a66e76db3e957d5db Mon Sep 17 00:00:00 2001 From: Olaf Hering <olh@suse.de> Date: Thu, 23 Mar 2006 21:50:59 +0100 Subject: [PATCH] correct the comment about stackpointer alignment in __boot_from_prom 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. The chain was yaboot -> zImage -> vmlinux PowerMac OpenFirmware does appearently not handle the ELF sections correctly. If yaboot was compiled in /usr/src/packages/BUILD/lilo-10.1.1/yaboot, then the stackpointer is unaligned. But the stackpointer is correct if yaboot is compiled in /tmp/yaboot. This bug triggered since 2.6.15, now prom_getprop is an inline function. gcc clears the lower bits, instead of just clearing the upper 32 bits. Signed-off-by: Olaf Hering <olh@suse.de> Signed-off-by: Paul Mackerras <paulus@samba.org> --- arch/powerpc/kernel/head_64.S | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) (limited to 'arch') diff --git a/arch/powerpc/kernel/head_64.S b/arch/powerpc/kernel/head_64.S index 35084f3a841b..7e7f7d243304 100644 --- a/arch/powerpc/kernel/head_64.S +++ b/arch/powerpc/kernel/head_64.S @@ -1544,7 +1544,11 @@ _STATIC(__boot_from_prom) mr r28,r6 mr r27,r7 - /* Align the stack to 16-byte boundary for broken yaboot */ + /* + * Align the stack to 16-byte boundary + * Depending on the size and layout of the ELF sections in the initial + * boot binary, the stack pointer will be unalignet on PowerMac + */ rldicr r1,r1,0,59 /* Make sure we are running in 64 bits mode */ -- cgit v1.2.3