I committed your current 64-asm patch from:
git://git.infradead.org/users/dwmw2/edk2.git
as edk2 r14045.
I tested Linux x86 & x86-64 boots for OVMF X64 built on Linux/GCC and
Win8/VS2012 with the change.
Thanks for the contribution,
-Jordan
On Tue, Jan 8, 2013 at 3:52 PM, David Woodhouse <dw...@infradead.org> wrote:
> We currently just jump to offset 0x200 in the kernel image, in 64-bit
> mode. This is completely broken. If it's a 32-bit kernel, we'll be
> jumping into the compressed data payload.
>
> If it's a 64-bit kernel, it'll work... but the 0x200 offset is
> explicitly marked as 'may change in the future', has already changed
> from 0x100 to 0x200 in the past with no fanfare, and bootloaders are
> instructed that they should look at the ELF header to find the offset.
> So although it does actually work today, it's still broken in the
> "someone needs to whipped for doing it this way" sense of the word.
>
> In fact, the same bug exists in other bootloaders so the 0x200 offset
> probably *is* now set in stone. But still it's only valid to use it if
> we *know* it's a 64-bit kernel. And we don't. There *is* no ELF header
> that we can look at when we're booting a bzImage, and we can't rely on
> it having a PE/COFF header either.
>
> The 32-bit entry point is always guaranteed to work, and we need to
> support it anyway. So let's just *always* use it, in 32-bit mode, and
> then we don't have to make up some horrible heuristics for detecting
> 32-bit vs. 64-bit kernels.
>
> Contributed-under: TianoCore Contribution Agreement 1.0
> Signed-off-by: David Woodhouse <david.woodho...@intel.com>
> ---
> Forget anything you've seen about the EFI boot stub; this part stands
> alone and is completely unrelated to that.
>
> If someone could carefully review my code for getting back into 32-bit
> mode, that would be much appreciated. I've tested that it happily boots
> both 32-bit and 64-bit kernels under qemu.
>
> It also wants converting to MS assembler form; I wasn't sure how to do
> the .code32/.code64 bits so figured it was best to leave it alone
> completely for now.
>
> diff --git a/edk2/OvmfPkg/Library/LoadLinuxLib/LinuxGdt.c
> b/edk2/OvmfPkg/Library/LoadLinuxLib/LinuxGdt.c
> index 4e20436..58c097c 100644
> --- a/edk2/OvmfPkg/Library/LoadLinuxLib/LinuxGdt.c
> +++ b/edk2/OvmfPkg/Library/LoadLinuxLib/LinuxGdt.c
> @@ -83,7 +83,11 @@ STATIC GDT_ENTRIES GdtTemplate = {
> 0x0, // base 0
> 0x0,
> 0x09A, // present, ring 0, data, expand-up, writable
> +#ifdef MDE_CPU_IA32
> 0x0CF, // page-granular, 32-bit
> +#else
> + 0x0AF, // compatibility mode
> +#endif
> 0x0,
> },
> //
> diff --git a/edk2/OvmfPkg/Library/LoadLinuxLib/X64/JumpToKernel.S
> b/edk2/OvmfPkg/Library/LoadLinuxLib/X64/JumpToKernel.S
> index 9ae755b..8a39333 100644
> --- a/edk2/OvmfPkg/Library/LoadLinuxLib/X64/JumpToKernel.S
> +++ b/edk2/OvmfPkg/Library/LoadLinuxLib/X64/JumpToKernel.S
> @@ -24,7 +24,37 @@ ASM_GLOBAL ASM_PFX(JumpToKernel)
>
> #------------------------------------------------------------------------------
> ASM_PFX(JumpToKernel):
> movq %rdx, %rsi
> - addq $0x200, %rcx
> - callq %rcx
> - ret
> + movq %rcx, %rbx
> + movq $0x10, %rax
> + shl $32, %rax
> + orq $1f, %rax
> + pushq %rax
> + retf
> +1: // Now in compatibility mode
> +.code32
> + movl $0x18, %eax
> + movl %eax, %ds
> + movl %eax, %es
> + movl %eax, %fs
> + movl %eax, %gs
> + movl %eax, %ss
> +
> + // Disable paging
> + movl %cr0, %eax
> + btcl $31, %eax
> + movl %eax, %cr0
> +
> + // Disable long mode in EFER
> + movl $0x0c0000080, %ecx
> + rdmsr
> + btcl $8, %eax
> + wrmsr
> +
> + // Disable PAE
> + movl %cr0, %eax
> + btcl $5, %eax
> + movl %eax, %cr0
> +
> + jmp %ebx
> +.code64
>
>
> --
> dwmw2
>
>
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