On 17.03.2014 23:15, Piotr Krysiuk wrote: > Hi, > > I occasionally need to boot a very old Linux kernel. > > This works fine with old versions of GRUB, from before relocator was > introduced. However the kernel cannot be started by recent versions > of GRUB - machine simply restarts as soon as GRUB passes control to > Linux. As mentioned above this affects very old Linux only, so very > few users (if any) would care. But as I have a patch, here it is. > > I tracked the issues to code initializing BSS that is used by old > Linux kernels. See code following "Clear BSS" on > https://git.kernel.org/cgit/linux/kernel/git/stable/linux-stable.git/tree/arch/x86_64/boot/compressed/head.S?h=linux-2.6.17.y#n57 > > AFAIK old Linux kernels do not provide information allowing boot > loader to determine end of BSS. As the consequence, current GRUB > may place GPT in the area overlapping with BSS sections of old > Linux kernels. The location of GPT was changed at the same time > when relocator was added, introducing regression. > Top of memory doesn't sound like a right place. Could you try with
> err = grub_relocator_alloc_chunk_align (rel, &ch, 0, > (0xa0000 - RELOCATOR_SIZEOF (32)), ... This will put GDT in low memory > In order to improve compatibility with these old kernels, we could > switch back to old strategy and simply place GPT close to end of > physical memory. > > Best regards, > > Piotr Krysiuk > --- > ChangeLog | 5 +++++ > grub-core/lib/i386/relocator.c | 2 +- > 2 files changed, 6 insertions(+), 1 deletion(-) > > diff --git a/ChangeLog b/ChangeLog > index 770269c..5a91e5e 100644 > --- a/ChangeLog > +++ b/ChangeLog > @@ -1,3 +1,8 @@ > +2014-03-17 Piotr Krysiuk <piot...@gmail.com> > + > + * grub-core/lib/i386/relocator.c: Moved GDT to end of physical memory > + to avoid collision with old Linux BSS. > + > 2014-02-28 Vladimir Serbinenko <phco...@gmail.com> > > * include/grub/i386/openbsd_bootarg.h: Add addr and frequency fields. > diff --git a/grub-core/lib/i386/relocator.c b/grub-core/lib/i386/relocator.c > index d2a1b27..523f669 100644 > --- a/grub-core/lib/i386/relocator.c > +++ b/grub-core/lib/i386/relocator.c > @@ -84,7 +84,7 @@ grub_relocator32_boot (struct grub_relocator *rel, > err = grub_relocator_alloc_chunk_align (rel, &ch, 0, > (0xffffffff - RELOCATOR_SIZEOF (32)) > + 1, RELOCATOR_SIZEOF (32), 16, > - GRUB_RELOCATOR_PREFERENCE_NONE, > + GRUB_RELOCATOR_PREFERENCE_HIGH, > avoid_efi_bootservices); > if (err) > return err; >
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