robin.thoni/ipxe - git rthoni.com

Michael Brown d1562c38a6 [librm] Prepare for long-mode memory map The bulk of the iPXE binary (the .textdata section) is physically relocated at runtime to the top of the 32-bit address space in order to allow space for an OS to be loaded. The relocation is achieved with the assistance of segmentation: we adjust the code and data segment bases so that the link-time addresses remain valid. Segmentation is not available (for normal code and data segments) in long mode. We choose to compile the C code with -mcmodel=kernel and use a link-time address of 0xffffffffeb000000. This choice allows us to identity-map the entirety of the 32-bit address space, and to alias our chosen link-time address to the physical location of our .textdata section. (This requires the .textdata section to always be aligned to a page boundary.) We simultaneously choose to set the 32-bit virtual address segment bases such that the link-time addresses may simply be truncated to 32 bits in order to generate a valid 32-bit virtual address. This allows symbols in .textdata to be trivially accessed by both 32-bit and 64-bit code. There is no (sensible) way in 32-bit assembly code to generate the required R_X86_64_32S relocation records for these truncated symbols. However, subtracting the fixed constant 0xffffffff00000000 has the same effect as truncation, and can be represented in a standard R_X86_64_32 relocation record. We define the VIRTUAL() macro to abstract away this truncation operation, and apply it to all references by 32-bit (or 16-bit) assembly code to any symbols within the .textdata section. We define "virt_offset" for a 64-bit build as "the value to be added to an address within .textdata in order to obtain its physical address". With this definition, the low 32 bits of "virt_offset" can be treated by 32-bit code as functionally equivalent to "virt_offset" in a 32-bit build. We define "text16" and "data16" for a 64-bit build as the physical addresses of the .text16 and .data16 sections. Since a physical address within the 32-bit address space may be used directly as a 64-bit virtual address (thanks to the identity map), this definition provides the most natural access to variables in .text16 and .data16. Note that this requires a minor adjustment in prot_to_real(), which accesses .text16 using 32-bit virtual addresses. Signed-off-by: Michael Brown <mcb30@ipxe.org>		9 年之前
contrib	[errdb] Strip platform error code for non-platform-generated errors	11 年之前
src	[librm] Prepare for long-mode memory map	9 年之前
COPYING	[legal] Update GPLv2 licence text	10 年之前
COPYING.GPLv2	[legal] Update GPLv2 licence text	10 年之前
COPYING.UBDL	[legal] Add support for the Unmodified Binary Distribution Licence	9 年之前
README	[doc] Re-add README file	14 年之前

iPXE README File

Quick start guide:

   cd src
   make

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