arm: Remaining issue with alignment of __log_buf in printk.c
jic23 at cam.ac.uk
Sun May 27 13:01:28 EDT 2012
Russell King - ARM Linux <linux at arm.linux.org.uk> wrote:
>On Sun, May 27, 2012 at 10:03:20AM -0600, Stephen Warren wrote:
>> On 05/27/2012 06:39 AM, Jonathan Cameron wrote:
>> > Hi All,
>> > My stargate 2 board refused to start and after bisection I ended
>> > up at the same patch that Stephen found an alignment issue in.
>> > Unfortunately Stephen's patch doesn't seem to have fixed the
>> > issue for me.
>> > https://lkml.org/lkml/2012/5/10/510 is the thread. Patch from
>> > Stephen is : f8450fca6ecdea38b5a882fdf6cd097e3ec8651c
>> > Increasing the alignement for 32 bit systems to 8 seems to do the
>> > job but I can't immediately think why...
>> > System is a pxa27x strong arm.
>First thing to point out is that PXA27x is Xscale, not StrongARM.
Sorry my mistake!
>> The first element in the structure type that's actually stored in the
>> __log_buf array is a u64; see struct log in kernel/printk.c.
>> on alignment rules, a u64 and a struct containing it might require a
>> 4-byte or 8-byte alignment. The following link implies this might
>> changed over time:
>> (see "64-bit data type alignment" a little below that anchor). I'm
>> sure what ABI the kernel expects to use internally, or your compiler;
>> perhaps you need the new EABI 8-byte alignment requirement for a u64
>> hence the struct as a whole, but Tegra (or my toolchain?) is OK with
>> older 4-byte alignment for a u64 or struct?
>> Further, I'm not sure if the following alignment selection logic:
>> > #if !defined(CONFIG_64BIT) ||
>> > #define LOG_ALIGN 4
>> > #else
>> > #define LOG_ALIGN 8
>> > #endif
>> ... uses the CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS for its intended
>> Russell, can you please comment here. Thanks.
>And most likely it's using EABI which does want 8 byte alignment.
Indeed I am using eabi.
>should probably be fixed for EABI builds.
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