Ah. I think I may have found the answer to at least part of my question, but would appreciate if someone could confirm...
Section 2.3.4 of the UEFI spec states: "Selectors are set to be flat and are otherwise not used." Section 3.2.4 of the Intel processor spec (Vol. 3A 3-7) states: "In 64-bit mode, segmentation is generally (but not completely) disabled, creating a flat 64-bit linear-address space... Note that the processor does not perform segment limit checks at runtime in 64-bit mode." So if I'm reading all this correctly... The value of the fields governing the interpretation of the segment limits (e.g., L and D/B) are "don't cares" in IA32e 64-bit mode. But what about fields not directly related to limit checks: e.g., P (Present) flag, and DPL (Descriptor Privilege Level)? Do their values not matter either? Thanks, Brett S. On Tue, Jun 7, 2016 at 8:46 AM, Brett Stahlman <[email protected]> wrote: > Just inside my 64-bit x64 EFI boot loader, I print out the contents of > the GDT to see how it was initialized by the firmware. I've tried > running the boot loader both in QEMU (OVMF) and VMware ESXi. In both > cases, the first 5 descriptors after the leading null descriptor look > like this: > > 0x000000000000ffff > > Note all the leading zeroes: in particular, flags such as D/B and L > being clear seem to suggest a GDT that's inappropriate for 64-bit long > mode. I've verified by looking at CR* registers and such that the > firmware has indeed placed me in IA32e "long mode" with identity > paging. This is what I would expect, in light of section 2.3.4 in the > UEFI spec. But why does the GDT have all leading 0's? > > Thanks, > Brett S. _______________________________________________ edk2-devel mailing list [email protected] https://lists.01.org/mailman/listinfo/edk2-devel
