On Wed, 1 Apr 2009, Linus Torvalds wrote: > > > On Wed, 1 Apr 2009, H. Peter Anvin wrote: > > > > implements handling for the backwards-incompatible(!) E820 handling in > > ACPI 3. > > I am _extremely_ nervous about this one. > > You do > > size = sizeof buf; /* ACPI-3 size */ > asm(.. "+c" (size) /* size might change */ > .. > if (size > 20 && !(buf.ext_flags & 1)) > continue; > > ie you are expecting that _all_ old pre-ACPI-3 BIOSES will always set size > to 20, or always write a low-bit-set value to that extended flag field > that doesn't even exist previously. Yes, this expects old BIOS to always return 20. No, it does not expect old BIOS to have any particular value in buf.ext_flags -- since that is examined only for size > 20. > I don't think that's likely true. Quite frankly, I'd expect a number of > BIOSen to entirely ignore %ecx, since it's irrelevant (it _has_ to be > bigger than 20 anyway on entry, and I doubt anybody really ever bothered > to test that it's 20 on exit). > > So at a _minimum_, I'd suggest that we set bug.ext_flags to 1 before the > call - so that if some random BIOS just leaves %ecx unchanged, it won't > mean that the area just gets ignored as a ACPI-3 entry. Good idea. Len Brown, Intel Open Source Technology Center -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
