x86: prepare cache-as-ram to allow multiple stages

In order to do a verification of romstage on x86 one needs to
run verstage which verifies romstage (and the memory init code).
However, x86 doesn't have SRAM like every other modern SoC so
managing the cache-as-ram region is especially critical.

First move all of the "shared" objects to the beginning of
the .car.data section. This change then ensures that each stage
using car.ld to link has the same consistent view of the addresses
of these fixed-sized objects in cache-as-ram. The CAR_GLOBALs can
be unique per stage. However, these variables are expected to have
a value of zero at the start of each stage. In order to allow a
stage to provide those semantics outside of the initial cache-as-arm
setup routine add _car_global_start and _car_global_end symbols.
Those symbols can be used to clear the CAR_GLOBALs for that stage.

Note that the timestamp region can't be moved out similarly to the
pre-ram cbmem console because the object storage of the timestamp
cache is used *after* cache-as-ram is torn down to indicate if the
cache should be used or not. Therefore, that timestamp needs to
migrated to ram. A logic change in src/lib/timestamp.c could
alleviate this requirement, but that task wasn't tackled in this

TEST=Built and booted glados.

Change-Id: I15e9f6b0c632ee5a2369da0709535d6cb0d94f61
Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: http://review.coreboot.org/11740
Tested-by: build bot (Jenkins)
Reviewed-by: Patrick Georgi <pgeorgi@google.com>
1 file changed