robin.thoni/ipxe - git rthoni.com

Michael Brown 54c5d08df1 [vesafb] Work around data corruption bug in bochs/qemu VBE implementation The vgabios used by bochs and qemu (and other virtualisation products) has a bug in its implementation of INT 10,4f00 which causes the high 16 bits of %ebx and %edx to become corrupted. The vgabios code uses a "pushaw"/"popaw" pair to preserve the low 16 bits of all non-segment registers. The vgabios code is compiled using bcc, which generates 8086-compatible code and so never touches the high 16 bits of the 32-bit registers. However, the function vbe_biosfn_return_controller_information() includes the line: size_64k = (Bit16u)((Bit32u)cur_info->info.XResolution * cur_info->info.XResolution * cur_info->info.BitsPerPixel) >> 19; which generates an implicit call to the "lmulul" function. This function is implemented in vbe.c as: ; helper function for memory size calculation lmulul: and eax, #0x0000FFFF shl ebx, #16 or eax, ebx SEG SS mul eax, dword ptr [di] mov ebx, eax shr ebx, #16 ret which modifies %eax, %ebx, and %edx (as a result of the "mul" instruction, which places its result into %edx:%eax). Work around this problem by marking %ebx and %edx as being clobbered by the call to INT 10,4f00. (%eax is already used as an output register, so does not need to be on the clobber list.) Reported-by: Oliver Rath <rath@mglug.de> Signed-off-by: Michael Brown <mcb30@ipxe.org>		11 years ago
contrib	[errdb] Strip platform error code for non-platform-generated errors	11 years ago
src	[vesafb] Work around data corruption bug in bochs/qemu VBE implementation	11 years ago
COPYING	Initial revision	19 years ago
COPYRIGHTS	[build] Rename gPXE to iPXE	14 years ago
README	[doc] Re-add README file	14 years ago

iPXE README File

Quick start guide:

   cd src
   make

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