On Mon, 2013-01-21 at 01:53 +0000, Li, Elvin wrote: > [Li, Elvin] It is unlucky that CSM32 does not support returning back > from legacy boot at all. If legacy boot is failed, a full function of > CSM16 normally keep in legacy environment and INT19 handler indicates > “No bootable device -- insert boot disk and press any key” screen. > EDK2 CSM32 can only work with such CSM16 and does not expect CSM16 > will return. And in legacy boot, we expect that CSM16 retries to boot > from all valid entries in BBS table, if no devices is bootable, CSM16 > will print the error message, this complied with BBS specification for > the legacy boot.
OK, thanks for the clarification. Is this 'fixed' in other UEFI implementations? I'm fairly sure I have some recent Intel boards on which I can select a legacy boot from the hard drive, and end up back in the boot menu because the 0xaa55 signature isn't on the first sector, so it doesn't jump to it. That's the situation in which the spec indicates that the Boot method should return, isn't it? (Admittedly, I get no *explanation* or error message, just back in the boot menu immediately as if my 'enter' key doesn't work, so I end up bashing it a few times before I notice the *quick* flash on the screen as I do so. But that's just a UI issue. It *does* seem to come back from attempting the legacy boot.) How does that work? > The other thing that confuses me is that the LegacyBiosPrepareToBootEfi > function is never called — even when I put a CD in the drive and it > *does* boot an EFI OS from it. Is that expected? > > [Li, Elvin] Are you sure you boot CD by a legacy boot option? Are you > seeing from debug message that legacy boot is invoked? My test is a Fedora install CD. The legacy boot option is isolinux, and the EFI boot is grub2. So it's always clear which one it's booted. When it boots the EFI grub2, LegacyBiosPrepareToBootEfi is never called. 'git grep PrepareToBootEfi' seems to confirm that there is nothing that *would* call it. -- dwmw2
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