On 01/07/19 20:22, Leif Lindholm wrote:
On Mon, Jan 07, 2019 at 07:29:47PM +0100, Laszlo Ersek wrote:
The UEFI spec (v2.7) explicitly requires EFI_GUID to be 64-bit aligned, unless specified otherwise. See in "Table 5. Common UEFI Data Types":
EFI_GUID -- 128-bit buffer containing a unique identifier value. Unless otherwise specified, aligned on a 64-bit boundary.
Indeed.
Whether edk2 satisfies that, and if so, how (by chance / by general build flags), I don't know. The code says,
/// /// 128 bit buffer containing a unique identifier value. /// Unless otherwise specified, aligned on a 64 bit boundary. /// typedef struct { UINT32 Data1; UINT16 Data2; UINT16 Data3; UINT8 Data4[8]; } GUID;
I think there may have been an expectation in "MdePkg/Include/Base.h" that the supported compilers would automatically ensure the specified alignment, given the structure definition.
But that would be expecting things not only not guaranteed by C, but something there is no semantic information suggesting would be useful for the compiler to do above. [...]
Agreed. I'm not saying the edk2 code is right, just guessing why the code might look like it does. This would not be the first silent assumption, I think.
Anyhow, I think it would be better to change the code than the spec.
Thanks, Laszlo