robin.thoni/ipxe - git rthoni.com

Michael Brown 87723a0f11 [libflat] Test A20 gate without switching to flat real mode Use the real-mode address ffff:0010 to access the linear address 0x100000, and so test whether or not the A20 gate is enabled without requiring a switch into flat real mode (or some other addressing mode). This speeds up CPU mode transitions, and also avoids breaking the NBP from IBM's Tivoli Provisioning Manager for Operating System Deployment. This NBP makes some calls to iPXE in VM86 mode rather than true real mode and does not correctly emulate our transition into flat real mode. Interestingly, Tivoli's VMM does allow us to switch into protected mode (though it patches our GDT so that we execute in ring 1 rather than ring 0). However, paging is still disabled and we have a 4GB segment limit. Being in ring 1 does not, therefore, restrict us in any meaningful way; this has been verified by deliberately writing garbage over Tivoli's own GDT (at address 0x02201010) during a nominally VM86-mode PXE API call. It's unclear precisely what protection this VMM is supposed to be offering. Suggested-by: Joshua Oreman <oremanj@rwcr.net> Signed-off-by: Michael Brown <mcb30@ipxe.org>		преди 14 години
contrib	[contrib] Remove extraneous errcodedb files	преди 14 години
src	[libflat] Test A20 gate without switching to flat real mode	преди 14 години
COPYING	Initial revision	преди 19 години
COPYRIGHTS	[build] Rename gPXE to iPXE	преди 14 години
README	[doc] Re-add README file	преди 14 години

iPXE README File

Quick start guide:

   cd src
   make

For any more detailed instructions, see http://ipxe.org