Re: [RFT PATCH] efi/x86: move x86 back to libstub

[Matt Fleming <matt-HNK1S37rvNbeXh+fF434Mdi2O/JbrIOy@public.gmane.org>]

On Mon, 06 Oct, at 01:06:43PM, Ard Biesheuvel wrote:
> This reverts commit 84be880560fb, which itself reverted my original
> attempt to move x86 from #include'ing .c files from across the tree
> to using the EFI stub built as a static library.
> 
> The issue that affected the original approach was that splitting
> the implementation into several .o files resulted in the variable
> 'efi_early' becoming a global with external linkage, which under
> -fPIC implies that references to it must go through the GOT. However,
> dealing with this additional GOT entry turned out to be troublesome
> on some EFI implementations. (GCC's visibility=hidden attribute is
> supposed to lift this requirement, but it turned out not to work on
> the 32-bit build.)
> 
> Instead, use a pure getter function to get a reference to efi_early.
> This approach results in no additional GOT entries being generated,
> so there is no need for any changes in the early GOT handling.
> 
> Cc: Maarten Lankhorst <maarten.lankhorst-Z7WLFzj8eWMS+FvcfC7Uqw@public.gmane.org>
> Cc: Josh Boyer <jwboyer-rxtnV0ftBwyoClj4AeEUq9i2O/JbrIOy@public.gmane.org>
> Cc: Linus Torvalds <torvalds-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>
> ---
> 
> Gents,
> 
> This is a request for testing: I would like to find out if this patch
> fixes Maarten's issue without breaking anything like it did for Josh
> and Linus the first time around.
> 
> 
>  arch/x86/boot/compressed/Makefile |  3 ++-
>  arch/x86/boot/compressed/eboot.c  |  8 ++++----
>  arch/x86/boot/compressed/eboot.h  | 16 ----------------
>  arch/x86/include/asm/efi.h        | 24 ++++++++++++++++++++++++
>  drivers/firmware/efi/Makefile     |  2 +-
>  5 files changed, 31 insertions(+), 22 deletions(-)

Ard, this is a very neat trick.

Thanks for taking the time to reimplement this, it's much appreciated.

Things work fine on my end, and I do have a Fedora 20/grub box in my
testing farm now, so I'm confident this is a good patch.

But if other people want to test it out, I'd be grateful of some more
Tested-by tags (I've already picked up Maarten's).

-- 
Matt Fleming, Intel Open Source Technology Center