> On May 9, 2015, at 10:30 PM, Jordan Justen <jordan.l.jus...@intel.com> wrote:
>
> On 2015-05-09 13:15:42, Ard Biesheuvel wrote:
>> According to the UEFIv2.5 spec section 6.2, the allocations returned
>> by the AllocatePool () boot service must be 8 byte aligned.
>>
>> So make our implementation conform to the spec, by rearranging the
>> pool head struct so that its size is always a multiple of 8 bytes.
>>
>> Contributed-under: TianoCore Contribution Agreement 1.0
>> Signed-off-by: Ard Biesheuvel <ard.biesheu...@linaro.org
>> <mailto:ard.biesheu...@linaro.org>>
>> ---
>> MdeModulePkg/Core/Dxe/Mem/Pool.c | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/MdeModulePkg/Core/Dxe/Mem/Pool.c
>> b/MdeModulePkg/Core/Dxe/Mem/Pool.c
>> index ac717fb65f7a..6f8f5cfb295d 100644
>> --- a/MdeModulePkg/Core/Dxe/Mem/Pool.c
>> +++ b/MdeModulePkg/Core/Dxe/Mem/Pool.c
>> @@ -26,9 +26,9 @@ typedef struct {
>> #define POOL_HEAD_SIGNATURE SIGNATURE_32('p','h','d','0')
>> typedef struct {
>> UINT32 Signature;
>> - UINT32 Reserved;
>> EFI_MEMORY_TYPE Type;
>> UINTN Size;
>> + UINTN Reserved;
>> CHAR8 Data[1];
>> } POOL_HEAD;
>
> So the issue is if sizeof(EFI_MEMORY_TYPE) == 4 on a 64-bit machine and the
> compiler doesn't 64-bit align the 64-bit Size field?
>
For the EFI ABI things are naturally aligned. So a 64-bit field is 64-bit
aligned by the compiler. This is not the default behavior for all compilers.
Thanks,
Andrew Fish
> With your change, couldn't there be an issue if the compiler made
> EFI_MEMORY_TYPE 64-bits, and once again chose not to 64-bit align Size
> and Reserved?
>
> Maybe this alignment should be handled in CoreAllocatePoolI? (Could we
> try to drop both Reserved and Data from that structure?)
>
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