Add __mca_table to the DISCARD list for the gate.lds linker script to
avoid broken linker references when linking the final vmlinux file.

Also add comment to include/asm-ia64/asmmacros.h to avoid anyone else
hitting this problem in the future.

Credits to James Bottomley <James.Bottomley@SteelEye.com> for spotting
the DISCARD list in gate.lds.S
Signed-off-by: NJes Sorensen <jes@sgi.com>
Signed-off-by: NTony Luck <tony.luck@intel.com>

Memory errors encountered by user applications may surface
when the CPU is running in kernel context.  The current code
will not attempt recovery if the MCA surfaces in kernel
context (privilage mode 0).  This patch adds a check for cases
where the user initiated the load that surfaces in kernel
interrupt code.

An example is a user process lauching a load from memory
and the data in memory had bad ECC.  Before the bad data
gets to the CPU register, and interrupt comes in.  The
code jumps to the IVT interrupt entry point and begins
execution in kernel context.  The process of saving the
user registers (SAVE_REST) causes the bad data to be loaded
into a CPU register, triggering the MCA.  The MCA surfaces in
kernel context, even though the load was initiated from
user context.

As suggested by David and Tony, this patch uses an exception
table like approach, puting the tagged recovery addresses in
a searchable table.  One difference from the exception table
is that MCAs do not surface in precise places (such as with
a TLB miss), so instead of tagging specific instructions,
address ranges are registers.  A single macro is used to do
the tagging, with the input parameter being the label
of the starting address and the macro being the ending
address.  This limits clutter in the code.

This patch only tags one spot, the interrupt ivt entry.
Testing showed that spot to be a "heavy hitter" with
MCAs surfacing while saving user registers.  Other spots
can be added as needed by adding a single macro.

Signed-off-by: Russ Anderson (rja@sgi.com)
Signed-off-by: NTony Luck <tony.luck@intel.com>

Initial git repository build. I'm not bothering with the full history,
even though we have it. We can create a separate "historical" git
archive of that later if we want to, and in the meantime it's about
3.2GB when imported into git - space that would just make the early
git days unnecessarily complicated, when we don't have a lot of good
infrastructure for it.

Let it rip!