Date: Sat, 21 Jan 2006 16:57:05 -0800 (PST) From: Doug White <dwhite@gumbysoft.com> To: current@freebsd.org Subject: i386 EFI loader -- need help Message-ID: <20060121163238.C62962@carver.gumbysoft.com>
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Hey folks, I've done some work to try to get the EFI loader to work on i386 and have run into some snags and gaps in my knowledge and could use a hand from people who have more experience with the boot process and toolchains and assembly code. There are 3 prinicipal parts that I need help with: 1. libefi elf32 exec() -- The code that actually goes between exiting EFI and jumping into the kernel image itself needs to be written. src/sys/boot/efi/libefi/elf_freebsd.c has the EFI part already taken care of. But from just after the call to ExitBootServices() down needs to do the necessary dance on i386 to start the kernel. I don't know what the expected environment is supposed to be and whether it needs to change from how EFI leaves things. EFI uses a flat space and disables paging when it exits. More details are in the EFI spec which is freely downloadable from Intel. 2. ELF32 self-relocator -- The self-relocation code in src/sys/boot/ia64/efi/start.S is in ia64 assembly and needs to be converted into i386 so the PE32+-wrapped-ELF-objects loader.efi binary can function. I'm not well versed enough in ia64 assembly or ELF in general to undertake this without going really, really slowly. :) 3. efi-app-ia32 toolchain target -- The spec defines PE32+ as the official binary format (32-bit PE with 64-bit relocations). Both us (via NetBSD?) and GNU cheat by having objcopy build a PE32+ binary but with a small shim that performs the ELF relocations. Our libbfd on i386 isn't configured with the efi-app-ia32 target. We include the efi-app-ia64 target on ia64 so this should just require adding some bits to the Makefile and building. _Should_. (This doesn't actually look so horrible so I'll give it a try.) After loader.efi is functional there is still the big job of conditionalizing BIOS calls in the kernel and providing EFI replacements where needed. A module to perform EFI calls from the kernel is also needed to allow access to the nvram variables and use the EFI ResetSystem() call if needed. If you need a test environment you can download the Sample Implementation from Intel which will give you a boot floppy you can pop in any PC and start up into EFI. I also have real hardware to test on that is big, white, and has a certain fruit for its logo. :) -- Doug White | FreeBSD: The Power to Serve dwhite@gumbysoft.com | www.FreeBSD.org
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