> -----Original Message----- > From: Måns Rullgård [mailto:[email protected]] > Sent: Saturday, October 12, 2013 1:29 AM > To: Piotr Wilczek > Cc: [email protected]; Tom Rini; Kyungmin Park > Subject: Re: [PATCH] disk:efi: avoid unaligned access on efi partition > > Piotr Wilczek <[email protected]> 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 <[email protected]> > > Signed-off-by: Kyungmin Park <[email protected]> > > CC: Tom Rini <[email protected]> > > --- > > 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. > Problem is that the legacy_mbr structure consists 'le16 unknown' field before 'partition_record' filed and the structure is packed. As a result the address of 'partition_record' filed is halfword aligned. The compiler uses str/ldr instructions (address must be 4-byte aligned) to copy u32 'lba' data thus causing unaligned access exception.
The best option would be to rearrange field in the structure but for other reasons I cannot do that. I will use put/get_unaligned as Albert suggested. Best regards Piotr Wilczek > -- > Måns Rullgård > [email protected] _______________________________________________ U-Boot mailing list [email protected] http://lists.denx.de/mailman/listinfo/u-boot
