[U-Boot] [PATCH] disk:efi: avoid unaligned access on efi partition

Måns Rullgård
2013-10-11T23:28:42Z

Piotr Wilczek <p.wilczek@samsung.com> writes:

> In this patch static variable and memcpy instead of an assignment
> are used to avoid unaligned access exception on some ARM platforms.
>
> Signed-off-by: Piotr Wilczek <p.wilczek@samsung.com>
> Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
> CC: Tom Rini <trini@ti.com>
> ---
> disk/part_efi.c | 6 ++++--
> 1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/disk/part_efi.c b/disk/part_efi.c
> index b7524d6..303b8af 100644
> --- a/disk/part_efi.c
> +++ b/disk/part_efi.c
> @@ -224,7 +224,8 @@ static int set_protective_mbr(block_dev_desc_t *dev_desc)
> p_mbr->signature = MSDOS_MBR_SIGNATURE;
> p_mbr->partition_record[0].sys_ind = EFI_PMBR_OSTYPE_EFI_GPT;
> p_mbr->partition_record[0].start_sect = 1;
> - p_mbr->partition_record[0].nr_sects = (u32) dev_desc->lba;
> + memcpy(&p_mbr->partition_record[0].nr_sects, &dev_desc->lba,
> + sizeof(dev_desc->lba));

Why is this assignment problematic? Note that the compiler may optimise
the memcpy() call into a plain assignment including any alignment
assumptions it was making in the original code.

The correct fix is either to ensure that pointers are properly aligned
or that things are annotated as potentially unaligned, whichever is more
appropriate.

--
M?ns Rullg?rd
mans at mansr.com