On 04/04/2018 02:32 PM, Alexander Graf wrote:
>
>
> On 03.04.18 21:59, Heinrich Schuchardt wrote:
>> The UEFI spec mandates that unaligned memory access should be enabled if
>> supported by the CPU architecture.
>>
>> This patch adds an empty weak function unaligned_access() that can be
>> overridden by an architecture specific routine.
>>
>> Signed-off-by: Heinrich Schuchardt <xypron.g...@gmx.de>
>> ---
>> cmd/bootefi.c | 13 +++++++++++++
>> include/asm-generic/unaligned.h | 3 +++
>> 2 files changed, 16 insertions(+)
>>
>> diff --git a/cmd/bootefi.c b/cmd/bootefi.c
>> index ba258ac9f3..412e6519ba 100644
>> --- a/cmd/bootefi.c
>> +++ b/cmd/bootefi.c
>> @@ -18,6 +18,7 @@
>> #include <memalign.h>
>> #include <asm/global_data.h>
>> #include <asm-generic/sections.h>
>> +#include <asm-generic/unaligned.h>
>> #include <linux/linkage.h>
>>
>> DECLARE_GLOBAL_DATA_PTR;
>> @@ -89,6 +90,15 @@ out:
>> return ret;
>> }
>>
>> +/*
>> + * Allow unaligned memory access.
>> + *
>> + * This routine is overridden by architectures providing this feature.
>> + */
>> +void __weak allow_unaligned(void)
>> +{
>> +}
>> +
>
> I'd prefer to guard the body of the function with an #ifdef CONFIG_ARM
> so everyone knows why it's there. Then call straight into a function
> provided in the ARM core code:
The same visibility can be achieved with a comment.
>
> static void allow_unaligned(void)
> {
> /* On ARM we prohibit unaligned accesses by default, enable them here */
> #if defined(CONFIG_ARM) && !defined(CONFIG_ARM64) &&
> !defined(CONFIG_CPU_V7M)
> mmu_enable_unaligned();
> #endif
> }
RISC-V also supports traps for unaligned access.
Using architecture specific flags outside arch/ is a mess.
We should not commit new sins but eliminate the existing deviations.
>
> And then in arch/arm/lib/cache-cp15.c:
>
> void mmu_enable_unaligned(void)
> {
> set_cr(get_cr() & ~CR_A);
> }
For some ARM architecture versions the bit is reserved and not used for
unaligned access. No clue what this function would do in this case.
That is why I used a weak function that does nothing if the CPU does not
support the flag.
Best regards
Heinrich
>
> I basically want to make sure this is as explicit as it gets :).
>
>
> Alex
>
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